A type of humidity that considers the mass of water vapor present per unit volume of space. Also considered as the density of the water vapor. It is usually expressed in grams per cubic meter.

This is considered the mixture of gases that make up the earth's atmosphere. The principal gases that compose dry air are Nitrogen (N2) at 78.09%, Oxygen (O2) at 20.946%, Argon (A) at 0.93%, and Carbon Dioxide (CO2) at 0.033%. One of the most important constituents of air and most important gases in meteorology is water vapor (H2O).

An extensive body of air throughout which the horizontal temperature and moisture characteristics are similar.

The soiling of the atmosphere by contaminants to the point that may cause injury to health, property, plant, or animal life, or prevent the use and enjoyment of the outdoors.

An instrument used to determine the altitude of an object with respect to a fixed level. The type normally used by meteorologists measures the altitude with respect to sea level pressure.

In meteorology, the measure of a height of an airborne object in respect to a constant pressure surface or above mean sea level.

An instrument which measures wind speed.

Of or relating to the area around the geographic South Pole, from 90 degrees South to the Antarctic Circle at approximately 66 1/2 degrees South latitude, including the continent of Antarctica. Along the Antarctic Circle, the sun does not set on the day of the summer solstice (approximately December 21st) and does not rise on the day of the winter solstice (approximately June 21st).

Although not officially recognized as a separate ocean body, it is commonly applied to those portions of the Atlantic, Pacific, and Indian Oceans that reach the Antarctic continent on their southern extremes.

Of or relating to the area around the geographic North Pole, from 90 degrees North to the Arctic Circle at approximately 66 1/2 degrees North latitude.

A term used for an extemely dry climate. The degree to which a climate lacks effective, life-promoting moisture. It is considered the opposite of humid when speaking of climates.

It is created by the radiant energy emission from the sun and its interaction with the earth's upper atmosphere over the middle and high latitudes. It is seen as a bright display of constantly changing light near the magnetic poles of each hemisphere. In the Northern Hemisphere, it is known as the aurora borealis or Northern Lights, and in the Southern Hemisphere, this phenomena is called the aurora australis.

The season of the year which occurs as the sun approaches the winter solstice, and characterized by decreasing temperatures in the mid-latitudes. Customarily, this refers to the months of September, October, and November in the North Hemisphere and the months of March, April, and May in the Southern Hemisphere. Astronomically, this is the period between the autumnal equinox and the winter solstice.

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A relatively rare form of lightning consisting of a luminous ball, often reddish in color, which moves rapidly along solid objects or remains floating in mid-air. Also known as globe lightning.

An instrument that continuously records a barometer's reading of atmospheric pressure. For an example, see aneroid barometer.

An instrument used to measure atmospheric pressure. Two examples are the aneroid barometer and the mercurial barometer.

The pressure exerted by the atmosphere at a given point. Its measurement can be expressed in several ways. One is in millibars. Another is in inches or millimeters of mercury (Hg). Also known as atmospheric pressure.

A system of estimating and reporting wind speeds. It is based on the Beaufort Force or Number, which is composed of the wind speed, a descriptive term, and the visible effects upon land objects and/or sea surfaces. The scale was devised by Sir Francis Beaufort (1777-1857), hydrographer to the British Royal Navy.

Thin, new ice on fresh or salt water that appears dark in color because of its transparency. Also refers to thin, transparent ice on road surfaces.

A severe weather condition characterized by low temperatures, winds 35 mph or greater, and sufficient falling and/or blowing snow in the air to frequently reduce visibility to1/4 mile or less for a duration of at least 3 hours. A severe blizzard is characterized by temperatures near or below 10 degrees Fahrenheit, winds exceeding 45 mph, and visibility reduced by snow to near zero.

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A temperature scale where water at sea level has a freezing point of 0 degrees C (Celsius) and a boiling point of +100 degrees C. More commonly used in areas that observe the metric system of measurement. Created by Anders Celsius in 1742. Same as Centigrade. In 1948, the Ninth General Conference on Weights and Measures replaced "degree centigrade" with "degree Celsius."

A type of foehn wind. Refers to the warm downslope wind in the Rocky Mountains that may occur after an intense cold spell when the temperature could rise by 20 to 40 degrees Fahrenheit in a matter of minutes. Also known as the Snow Eater.

A glossy, clear, or translucent ice formed by the relatively slow freezing of large supercooled in water droplets. The droplets spread out over an object, such as an aircraft wing's leading edge, prior to complete freezing and forms a sheet of clear ice. Often synonymous with glaze.

The historical record and description of average daily and in seasonal weather events that help describe a region. Statistics are generally drawn over several decades. The word is derived from the Greek klima, meaning inclination, and reflects the importance early scholars attributed to the sun's influence.

A visible collection of minute particle matter, such as water droplets and/or ice crystals, in the free air. A cloud forms in the atmosphere as a result of condensation of water vapor. Condensation nuclei, such as in smoke or dust particles, form a surface upon which water vapor can condense.

The leading edge of an advancing cold air mass that is underrunning and displacing the warmer air in its path. Generally, with the passage of a cold front, the temperature and humidity decrease, the pressure rises, and the wind shifts (usually from the southwest to the northwest in the Northern Hemisphere). Precipitation is generally at and/or behind the front, and with a fast-moving system, a squall line may develop ahead of the front. See occluded front and warm front.

The process by which water vapor undergoes a change in state from a gas to a liquid. It is the opposite physical process of evaporation.

The process of a substance going directly from a vapor form (water vapor) to a solid (ice) at the same temperature, without going through the liquid phase (water). The opposite of sublimation.

A horizontal movement of water, such as the Gulf Stream off the east coast of North America, or air, such as the jet stream.

An area of closed pressure circulation with rotating and converging winds, the center of which is a relative pressure minimum. The circulation is counterclockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere. Also called a low pressure system and the term used for a tropical cyclone in the Indian Ocean. Other phenomena with cyclonic flow may be referred to by this term, such as dust devils, tornadoes, and tropical and extratropical systems. The opposite of an anticyclone or a high pressure system.

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The first appearance of light in the eastern sky before sunrise. It marks the beginning of morning twilight. The visual display is created by the scattering of light reaching the upper atmosphere prior to the sun's rise to the observer's horizon. Also known as daybreak.

Considered a basic unit of time as defined by the earth's motion. It represents the time needed for one complete revolution of the earth about its own axis. Also know as a sidereal day, it is approximately equal to 23 hours, 56 minutes, and 4.09 seconds. See night.

A measure of temperature difference representing a single division on a temperature scale. See Celsius, Fahrentheit, and Kelvin scales.

Density altitude is a measure used primarily by pilots, high-performance engine mechanics and long-range shooters. The density altitude is a measure of the density of the air, given in units of distance. It is a function of temperature, relative humidity and air pressure.

Condensation in the form of small water drops that forms on grass and other small objects near the ground when the temperature has fallen to the dew point, generally during the nighttime hours.

The dew point is the temperature at which dew would form assuming all other conditions remained the same. The dew point is a function of the air temperature and humidy. The dew point temperature can never be higher than the air temperature. If the dew point temp and air temp are the same, than the humidity must be 100%.
Okay, that's fine, but what does it really mean? The dew point is a very good measure of comfort. If the dew point is high, the temperature and humidity must also be high, and you are probably sweating profusely even while standing still. If the dew point is low, then either the temperature or humidity or both are very low, and you are feeling quite comfortable. This is a better guage for comfort than temperature or humidity alone. It could be quite warm but very dry (low dew point) and you would feel comfortable. It could also be very humid but cool or cold (low dew point) and you would feel comfortable. The temperature to which air must be cooled at a constant pressure to become saturated.

The name given to the very hot summer weather that may persists for four to six weeks between mid-July through early September in the United States. In western Europe, this period may exist from the first week in July to mid- August and is often the period of the greatest frequency of thunder. Named for Sirius, the Dog Star, which lies in conjunction with the sun during this period, it was once believed to intensify the sun's heat during the summer months.

A nautical term for the equatorial region of light winds between the trade winds of the two hemispheres.

Abnormal dry weather for a specific area that is sufficiently prolonged for the lack of water to cause serious hydrological imbalance.

A thermometer used to measure the ambient temperature. The temperature recorded is considered identical to air temperaure. One of the two therometers that make up a psychrometer.

The period of waning light from the time of sunset to dark. See twilight and dawn.

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A sudden, transient motion or trembling of the earth's crust, resulting from the waves in the earth caused by faulting of the rocks or by volcanic activity.

The obscuring of one celestial body by another. See lunar eclipse or solar eclipse.

The cyclical warming of East Pacific Ocean sea water temperatures off the western coast of South America that can result in significant changes in weather patterns in the United States and elsewhere. This occurs when warm equatorial waters move in and displace the colder waters of the Humbolt Current, cutting off the upwelling process.

The point at which the ecliptic intersects the celestial equator. Days and nights are most nearly equal in duration. In the Northern Hemisphere, the vernal equinox falls on or about March 20 and the autumnal equinox on or about September 22.

The physical process by which a liquid, such as water, is tranformed into a gaseous state, such as water vapor. It is the opposite physical process of condensation.

The center of a tropical storm or hurricane, characterized by a roughly circular area of light winds and rain-free skies. An eye will usually develop when the maximum sustained wind speeds exceed 78 mph. It can range in size from as small as 5 miles to up to 60 miles, but the average size is 20 miles. In general, when the eye begins to shrink in size, the storm is intensifying.

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A temperature scale where water at sea level has a freezing point of +32 degrees F (Fahrenheit) and a boiling point of +212 degrees F. More commonly used in areas that observe the English system of measurement. Created in 1714 by Gabriel Daniel Fahrenheit (1696-1736), a German physicist, who also invented the alcohol and mercury thermometers.

A flood that rises and falls quite rapidly with little or no advance warning, usually as the result of intense rainfall over a relatively small area. Flash floods can be caused by situations such as a sudden excessive rainfall, the failure of a dam, or the thaw of an ice jam.

High water flow or an overflow of rivers or streams from their natural or artificial banks, inundating adjacent low lying areas.

Level land that may be submerged by flood waters.

A visible aggregate of minute water droplets suspended in the atmosphere at or near the surface of the earth, reducing horizontal visibility to less than 5/8 statute miles. It is created when the temperature and the dew point of the air have become the same, or nearly the same, and sufficient condensation nuclei are present. It is reported as "FG" in an observation and on the METAR.

A statement of expected future occurrences. Weather forecasting includes the use of objective models based on certain atmospheric parameters, along with the skill and experience of a meteorologist. Also called a prediction.

The process of changing a liquid to a solid. The temperature at which a liquid solidifies under any given set of conditions. Pure water under atmospheric pressure freezes at 0 degrees Celsius or 32 degrees Fahrenheit. It is the opposite of fusion. In oceanography, the freezing point of water is depressed with increasing salinity.

The covering of ice crystals that forms by direct sublimation on exposed surfaces whose temperature is below freezing.

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On the Beaufort Wind Scale, a wind with speeds from 28 to 55 knots (32 to 63 miles per hour). For marine interests, it can be categorized as a moderate gale (28 to 33 knots), a fresh gale (34 to 40 knots), a strong gale (41 to 47 knots), or a whole gale (48 to 55 knots). In 1964, the World Meteorological Organization defined the categories as near gale (28 to 33 knots), gale (34 to 40 knots), strong gale (41 to 47 knots), and storm (48 to 55 knots).

The overall warming of the earth's lower atmosphere primarily due to carbon dioxide and water vapor which permit the sun's rays to heat the earth, but then restrict some heat-energy from escaping back into space.

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Precipitation that originates in convective clouds, such as cumulonimbus, in the form of balls or irregular pieces of ice, which comes in different shapes and sizes. Hail is considered to have a diameter of 5 millimeter or more; smaller bits of ice are classified as ice pellets, snow pellets, or graupel. Individual lumps are called hailstones. It is reported as "GR" in an observation and on the METAR. Small hail and/or snow pellets is reported as "GS" in an observation and on the METAR.

A form of energy transferred between two systems by virtue of a difference in temperature. The first law of thermodynamics demonstrated that the heat absorbed by a system may be used by the system to do work or to raise its internal energy.

The effect of excessive heat, particularly when combined with high humidity, on a human being. Signs of heat exhaustion include a general weakness, heavy sweating and clammy skin, dizziness and/or fainting, and muscle cramps.

The combination of air temperature and humidity that gives a description of how the temperature feels. This is not the actual air temperature. For an example, check out the heat index chart.

Lightning that appears as a glowing flash on the horizon. It is actually lightning occurring in distant thunderstorms, just over the horizon and too far away for thunder to be heard.

Introduced to the body by overexposure to high temperatures, particularly when accompanied by high humidity. The signs of heat stroke include when an individual's body temperature is greater than 105 degrees Fahrenheit, the skin is hot and dry, there is a rapid and irregular pulse, perspiration has stopped, and one has lost consciousness. Seek imsfimageste medical aid. May be called a sun-stroke when caused by direct exposure to the sun.

A period of abnormally and uncomfortably hot weather. It could last from several days to several weeks. The Weather Channel uses the following criteria for a heat wave: a minimum of ten states must have 90 degree plus temperatures and the temperatures must be at least five degrees above normal in parts of that area for at least two days or more.

Located between 30 degrees North and South in the vicinity of the equator, this area typically has calm or light and variable winds. Another name for the equatorial trough, the Intertropical Convergence Zone (ITCZ), or the doldrums.

The amount of water vapor in the air. It is often confused with relative humidity or dew point. Types of humidity include absolute humidity, relative humidity,and specific humidity.

The name for a tropical cyclone with sustained winds of 74 miles per hour (65 knots) or greater in the North Atlantic Ocean, Caribbean Sea, Gulf of Mexico, and in the eastern North Pacific Ocean. This same tropical cyclone is known as a typhoon in the western Pacific and a cyclone in the Indian Ocean.

Any any form of atmospheric water vapor, including those blown by the wind off the earth's surface. Liquid or solid water formation that is suspended in the air includes clouds, fog, ice fog, and mist. Drizzle and rain are example of liquid precipitation, while freezing drizzle and freezing rain are examples of freezing precipitation. Solid or frozen precipitation includes ice pellets, hail, snow, snow pellets, snow grains, and ice crystals. Water vapor that evaporates before reaching the ground is virga. Examples of liquid or solid water particles that are lifted off the earth's surface by the wind includes drifting and blowing snow and blowing spray. Dew, frost, rime, and glaze are examples of liquid or solid water deposits on exposed objects.

An instrument that measures the water vapor content of the atmosphere. See the psychrometer as an example.

Occurs when the core temperature of one's body falls below normal. It is the failure of the body to maintain adequate production of heat under conditions of extreme cold.

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ICE The solid form of water. It can be found in the atmosphere in the form of ice crystals, snow, ice pellets, and hail, for example.

Precipitation in the form of slowly falling, singular or unbranched ice needles, columns, or plates. They make up cirriform clouds, frost, and ice fog. Also, they produce optical phenomena such as halos, coronas, and sun pillars. May be called "diamond dust". It is reported as "IC" in an observation and on the METAR.

An accumulation of broken river ice caught in a narrow channel, frequently producing local flooding. Primarily occurs during a thaw in the late winter or early spring.

A severe weather condition characterized by falling freezing precipitation. Such a storm forms a glaze on objects, creating hazardous travel conditions and utility problems.

Ice that forms in the shape of a narrow cone hanging point down. It usually forms when liquid water from a sheltered or heated source comes in contact with below-freezing air and freezes more or less rapidly as it flows.

The forming or depositing of ice on an object. See glaze.

The name comes from the use of mercurial barometers which equate the height of a column of mercury with air pressure. One inch of mercury is equivalent to 33.86 millibars or 25.40 millimeters. See barometric pressure. First divised in 1644 by Evangelista Torricelli (1608-1647), an Italian physicist and mathematician, to explain the fundamental principles of hydromechanics.

A period of abnormally warm weather in mid to late autumn with clear skies and cool nights. A first frost normally precedes this warm spell.

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A region of accelerated wind speed along the axis of a jet stream.

A narrow band of strong winds usually found at elevations from 20000 to 50000 feet.

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A nautical unit of speed equal to the velocity at which one nautical mile is traveled in one hour. Used primarily by marine interests and in weather observations. A knot is equivalent to 1.151 statute miles per hour or 1.852 kilometers per hour.

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A sudden and visible discharge of electricity produced in response to the build up of electrical potential between cloud and ground, between clouds, within a single cloud, or between a cloud and surrounding air. For an example, see ball lightning.

An eclipse of the moon occurs when the earth is in a direct line between the sun and the moon. The moon does not have any light of its own, instead, it reflects the sun's light. During a lunar eclipse, the moon is in the earth's shadow. It will often look dim and sometimes copper or orange in color.

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An instrument used for measuring the change in atmospheric pressure. It uses a long glass tube, open at one end and closed at the other. After first filling the open end with mercury, it is then temporarily sealed and placed into a cistern of mercury. A nearly perfect vacuum is established at the closed end after the mercury descends. The height of the column of mercury in the tube is a measurement of air pressure. As atmospheric pressure increases, the mercury is forced from the cistern up the tube; when the atmospheric pressure decreases, the mercury flows back into the cistern. Measurement is taken in inches of mercury. Although mercurial barometers are very accurate, practicality has led observers to use aneroid barometers. First used by Evangelista Torricelli (1608-1647), an Italian physicist and mathematician, to explain the fundamental principles of hydromechanics.

The science and study of the atmosphere and atmospheric phenomena. Various areas of meteorology include agricultural, applied, astrometerology, aviation, dynamic, hydrometeorology, operational, and synoptic, to name a few. A scientist who studies the atmosphere and atmospheric phenomena.

The latitude belt roughly between 35 and 65 degrees North and South. Also referred to as the temperate region.

A collection of microscopic water droplets suspended in the atmosphere. It does not reduce visibility as much as fog and is often confused with drizzle.

Refers to the water vapor content in the atmosphere, or the total water, liquid, solid or vapor, in a given volume of air.

The seasonal shift of winds created by the great annual temperature variation that occurs over large land areas in contrast with associated ocean surfaces. The monsoon is associated primarily with the moisture and copious rains that arrive with the southwest flow across southern India. The name is derived from the word mausim, Arabic for season. This pattern is most evident on the southern and eastern sides of Asia, although it does occur elsewhere, such as in the southwestern United States.

Fast moving soil, rocks and water that flow down mountain slopes and canyons during a heavy a downpour of rain.

A subjective term for warm and excessively humid weather.

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Rarely seen clouds of tiny ice particles that form approximately 75 to 90 kilometers above the earth's surface. They have been seen only during twilight (dusk and dawn) during the summer months in the higher latitudes. They may appear bright against a dark night sky, with a blue-silver color or orange-red.

A cyclonic storm occurring off the east coast of North America. These winter weather events are notorious for producing heavy snow, rain, and tremendous waves that crash onto Atlantic beaches, often causing beach erosion and structural damage. Wind gusts associated with these storms can exceed hurricane force in intensity. A nor'easter gets its name from the continuously strong northeasterly winds blowing in from the ocean ahead of the storm and over the coastal areas.

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In meteorology, the evaluation of one or more meteorological elements, such as temperature, pressure, or wind, that describe the state of the atmosphere, either at the earth's surface or aloft. An observer is one who records the evaluations of the meteorological elements.

The amount of sky cover for a cloud layer that is 8/8ths, based on the summation layer amount for that layer.

A nearly colorless gas and a form of oxygen (O2). It is composed of an oxygen molecule made up of three oxygen atoms instead of two.

An atmospheric layer that contains a high proportion of oxygen that exists as ozone. It acts as a filtering mechanism against incoming ultraviolet radiation. It is located between the troposphere and the stratosphere, around 9.5 to 12.5 miles (15 to 20 kilometers) above the earth's surface.

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Any and all forms of water, liquid or solid, that falls from clouds and reaches the ground. This includes drizzle, freezing drizzle, freezing rain, hail, ice crystals, ice pellets, rain, snow, snow pellets, and snow grains. The amount of fall is usually expressed in inches of liquid water depth of the substance that has fallen at a given point over a specified time period.

A wind that blows from one direction more frequently than any other during a given period, such as a day, month, season, or year.

An instrument used to measure water vapor content of the atmosphere. It consists of two thermometers, a wet bulb and dry bulb. May also be referred to as a sling psychrometer.

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Precipitation in the form of liquid water droplets greater than 0.5 mm. If widely scattered, the drop size may be smaller. It is reported as "R" in an observation and on the METAR. The intensity of rain is based on rate of fall. "Very light" (R--) means that the scattered drops do not completely wet a surface. "Light" (R-) means it is greater than a trace and up to 0.10 inch an hour. "Moderate" (R) means the rate of fall is between 0.11 to 0.30 inch per hour. "Heavy" (R+) means over 0.30 inch per hour.

A luminous arc featuring all colors of the visible light spectrum (red, orange, yellow, green, blue, indigo, and violet). It is created by refraction, total reflection, and the dispersion of light. It is visible when the sun is shining through air containing water spray or raindrops, which occurs during or imsfimagestely after a rain shower. The bow is always observed in the opposite side of the sky from the sun.

A type of humidity that considers the ratio of the actual vapor pressure of the air to the saturation vapor pressure. It is usually expressed in percentage.

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To treat or charge something to the point where no more can be absorbed, dissolved, or retained. In meteorology, it is used when discussing the amount of water vapor in a volume of air.

The point when the water vapor in the atmosphere is at its maximum level for the existing temperature.

A diurnal coastal breeze that blows onshore, from the sea to the land. It is caused by the temperature difference when the surface of the land is warmer than the adjacent body of water. Predominate during the day, it reaches its maximum early to mid afternoon. It blows in the opposite direction of a land breeze.

Precipitation from a convective cloud that is characterized by its sudden beginning and ending, changes in intensity, and rapid changes in the appearance of the sky. It occurs in the form of rain (SHRA), snow (SHSN), or ice (SHPE). It is reported as "SH" in an observation and on the METAR.

The vault-like apparent surface against which all aerial objects are seen from the earth.

Also known as ice pellets, it is winter precipitation in the form of small bits or pellets of ice that rebound after striking the ground or any other hard surface. It is reported as "PE" in an observation and on the METAR.

Snow or ice on the ground that has been reduced to a softy watery mixture by rain and/or warm temperatures.

Frozen precipitation in the form of white or translucent ice crystals in complex branched hexagonal form. It most often falls from stratiform clouds, but can fall as snow showers from cumuliform ones. It usually appears clustered into snowflakes. It is reported as "SN" in an observation and on the METAR.

The season of the year which occurs as the sun approaches the summer solstice, and characterized by increasing temperatures in the mid-latitudes. Customarily, this refers to the months of March, April, and May in the North Hemisphere, and the months of September, October, and November in the Southern Hemisphere. Astronomically, this is the period between the vernal equinox and the summer solstice.

Astronomically, this is the period between the summer solstice and the autumnal equinox. It is characterized as having the warmest temperatures of the year, except in some tropical regions. Customarily, this refers to the months of June, July, and August in the North Hemisphere, and the months of December, January, and February in the Southern Hemisphere.

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The measure of molecular motion or the degree of heat of a substance. It is measured on an arbitrary scale from absolute zero, where the molecules theoretically stop moving. It is also the degree of hotness or coldness. In surface observations, it refers primarily to the free air or ambient temperature close to the surface of the earth.

A warm spell of weather when ice and snow melt. To free something from the binding action of ice by warming it to a temperature above the melting point of ice.

An instrument used for measuring temperature. The different scales used in meteorology are Celsius, Fahrenheit, and Kelvin or Absolute.

The sound emitted by rapidly expanding gases along the channel of a lightning discharge. Over three-quarters of lightning's electrical discharge is used in heating the gases in the atmosphere in and imsfimagestely around the visible channel. Temperatures can rise to over 10,000 degrees Celsius in microseconds, resulting in a violent pressure wave, composed of compression and rarefaction. The rumble of thunder is created as one's ear catches other parts of the discharge, the part of the lightning flash nearest registering first, then the parts further away.

Produced by a cumulonimbus cloud, it is a microscale event of relatively short duration characterized by thunder, lightning, gusty surface winds, turbulence, hail, icing, precipitation, moderate to extreme up and downdrafts, and under the most severe conditions, tornadoes.

The periodic rising and falling of the earth's oceans and atmosphere. It is the result of the tide-producing forces of the moon and the sun acting on the rotating earth. This propagates a wave through the atmosphere and along the surface of the earth's waters.

A violently rotating column of air in contact with and extending between a convective cloud and the surface of the earth. It is the most destructive of all storm-scale atmospheric phenomena. They can occur anywhere in the world given the right conditions, but are most frequent in the United States in an area bounded by the Rockies on the west and the Appalachians in the east.

An ocean wave with a long period that is formed by an underwater earthquake or landslide, or volcanic eruption. It may travel unnoticed across the ocean for thousands of miles from its point of origin and builds up to great heights over shallower water. Also known as a seismic sea wave, and incorrectly, as a tidal wave.

A slang term used in the United States for a tornado.

The name for a tropical cyclone with sustained winds of 74 miles per hour (65 knots) or greater in the western North Pacific Ocean. This same tropical cyclone is known as a hurricane in the eastern North Pacific and North Atlantic Ocean, and as a cyclone in the Indian Ocean.

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Electromagnetic radiation that has a wavelength shorter than visible light and longer than x-rays. Although it accounts for only 4 to 5 percent of the total energy of insolation, it is responsible for many complex photochemical reactions, such as fluorescence and the formation of ozone.

A small scale current of air with vertical motion. If there is enough moisture, then it may condense, forming a cumulus cloud, the first step towards thunderstorm development. Contrast with a downdraft.

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The pressure exerted by the molecules of a given vapor. In meteorology, it is considered as the part of total atmospheric pressure due to the water vapor content. It is independent of other gases or vapors.

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The leading edge of an advancing warm air mass that is replacing a retreating relatively colder air mass. Generally, with the passage of a warm front, the temperature and humidity increase, the pressure rises, and although the wind shifts (usually from the southwest to the northwest in the Northern Hemisphere), it is not as pronounced as with a cold frontal passage. Precipitation, in the form of rain, snow, or drizzle, is generally found ahead of the surface front, as well as convective showers and thunderstorms. Fog is common in the cold air ahead of the front. Although clearing usually occurs after passage, some conditions may produced fog in the warm air. See occluded front and cold front.

A forecast issued when severe weather has developed, is already occurring and reported, or is detected on radar. Warnings state a particular hazard or imminent danger, such as tornadoes, severe thunderstorms, flash and river floods, winter storms, heavy snows, etc.

Refers to the chemical compound, H2O, as well as its liquid form. At atmospheric temperatures and pressures, it can exist in all three phases: solid (ice), liquid (water), and gaseous (water vapor). It is a vital, life- sustaining part of life on earth.

The state of the atmosphere at a specific time and with respect to its effect on life and human activities. It is the short term variations of the atmosphere, as opposed to the long term, or climatic, changes. It is often referred to in terms of brightness, cloudiness, humidity, precipitation, temperature, visibility, and wind.

Originally used as a wind vane, it is an instrument that indicates the wind direction. The name developed based on observations on what kind of weather occurred with certain wind directions. Creative designs often adorn the tops of barns and houses.

Dependent on the temperature and the humidity of the air, it is the difference between the dry bulb and the wet bulb readings.

A thermometer used to measure the lowest temperature in the ambient atmosphere in its natural state by evaporating water from a wet muslin- covered bulb of a thermometer. The wet bulb temperature is used to compute dew point and relative humidity. One of the two therometers that make up a psychrometer.

Air that flows in relation to the earth's surface, generally horizontally. There are four areas of wind that are measured: direction, speed, character (gusts and squalls), and shifts. Surface winds are measured by wind vanes and anemometers, while upper level winds are detected through pilot balloons, rawin, or aircraft reports.

The calculation of temperature that takes into consideration the effects of wind and temperature on the human body. Describes the average loss of body heat and how the temperature feels. This is not the actual air temperature. For an example, check out the wind chill chart.

The direction from which the wind is blowing. For example, an easterly wind is blowing from the east, not toward the east. It is reported with reference to true north, or 360 degrees on the compass, and expressed to the nearest 10 degrees, or to one of the 16 points of the compass (N, NE, etc.).

The rate of the motion of the air on a unit of time. It can be measured in a number of ways. In observing, it is measured in knots, or nautical miles per hour. The unit most often used in the United States is miles per hour.

Astronomically, this is the period between the winter solstice and the vernal equinox. It is characterized as having the coldest temperatures of the year, when the sun is primarily over the opposite hemisphere. Customarily, this refers to the months of December, January, and February in the North Hemisphere, and the months of June, July, and August in the Southern Hemisphere.

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The interval required for the earth to complete one revolution around the sun. A sidereal year, which is the time it take for the earth to make one absolute revolution around the sun, is 365 days, 6 hours, 9 minutes, and 9.5 seconds. The calendar year begins at 12 o'clock midnight local time on the night of December 31st-January 1st. Currently, we operate under the Gregorian calendar of 365 days, with 366 days every four years, a leap year. The tropical year, also called the mean solar year, is dependent on the seasons. It is the interval between two consecutive returns of the sun to the vernal equinox. In 1900, that took 365 days, 5 hours, 48 minutes, and 46 seconds, and it is decreasing at the rate of 0.53 second per century.

Snow that is given golden, or yellow, appearance by the presence of pine or cypress pollen in it.

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One of several names for the twenty-four hour time which is used throughout the scientific and military communities. Other names for this time measurement are Universal Time Coordinate (UTC) or Greenwich Mean Time (GMT).

Are EMFs Hazardous to Our Health?

Are EMFs Hazardous to Our Health?

Can electromagnetic fields (EMF) from power lines, home wiring, airport and military radar, substations, transformers, computers and appliances cause brain tumors, leukemia, birth defects, miscarriages, chronic fatigue, headaches, cataracts, heart problems, stress. nausea, chest pain, forgetfulness, cancer and other health problems?

Numerous studies have produced contradictory results, yet some experts are convinced that the threat is real.

Dr. David Carpenter, Dean at the School of Public Health, State University of New York believes it is likely that up to 30% of all childhood cancers come from exposure to EMFs. The Environmental Protection Agency (EPA) warns "There is reason for concern" and advises prudent avoidance".

Martin Halper, the EPA's Director of Analysis and Support says "I have never seen a set of epidemiological studies that remotely approached the weight of evidence that we're seeing with EMFs. Clearly there is something here."

Concern over EMFs exploded after Paul Brodeur wrote a series of articles in the New Yorker Magazine in June 1989. Because of Paul Brodeur's reputation. his articles had a catalytic effect on scientists, reporters and concerned people throughout the world.

In November 1989, the Department of Energy reported that "It has now become generally accepted that there are, indeed, biological effects due to field exposure."

The EMF issue gained more publicity in 1990 when alarming reports appeared in Time, the Wall Street Journal, Business Week and popular computer publications. ABC's Ted Koppel and CBS's Dan Rather both aired special segments on EMFs.

In addition to the long-term health concerns, buying a house with high fields will be an economic disaster. In a few years, when power line radiation is as well known as asbestos and radon, a house with high fields will be practically impossible to sell. Already there are hundreds of lawsuits regarding EMFs and property devaluation.

EPA Says the Threat Is Real

By 1990, over one hundred studies had been conducted worldwide. Of these, at least two dozen epidemiological studies on humans indicated a link between EMFs and serious health problems. In response to public pressure, the Environmental Protection Agency IEPA) began reviewing and evaluating the available literature.

In a draft report issued in March 1990, the EPA recommended that EMFs be classified as a Class B carcinogen -- -a "probable human carcinogen and joined the ranks of formaldehyde, DDT, dioxins and PCBs.

After the EPA draft report was released, utility, military and computer lobbyists came down hard on the EPA. The EPA's final revision did NOT classify EMFs as a Class B carcinogen Rather, the following explanation was added:"

At this time such a characterization regarding the link between cancer and exposure to EMFs is not appropriate because the basic nature of the interaction between EMFs and biological processes leading to cancer is not understood."

Curiously, this rather unusual logic appears on the same page as the following: "In conclusion, several studies showing leukemia, Iymphoma and cancer of the nervous system in children exposed to supported by similar findings in adults in several/ occupational studies also involving electrical power frequency exposures, show a consistent pattern of response that suggest a causal link. "

When questioned about the contradictory nature of these statements, the EPA responded that it was "not appropriate" to use the probable carcinogen label until it could demonstrate how EMFs caused cancer and exactly how much EMF is harmful.

This explanation does not satisfy many critics who claim that the EPAs upper management was influenced by political and economic considerations exerted by utility, computer and military lobbyists.

How Do I Measure EMFs?

A Gauss is a common unit of measurement of magnetic field strength. A Gauss meter is an instrument which measures the strength of magnetic fields. Inside a Gauss meter there is a coil of thin wire, typically with hundreds of turns. As a magnetic field radiates through the coil, it induces a current, which is amplified by the circuitry inside the Gauss meter.

Gauss meters may vary in the strength of the magnetic field they are capable of measuring. A meter used for measuring EMFs from power lines, transformers, substations and appliances around the home, for example, should be able to measure as low as .1 mg.

Gauss meters vary widely in price and accuracy. Meters have either a single axis coil or a triple axis coil. Single axis meters are much simpler than triple axis meters to manufacture and thus, are less expensive.

To use a single axis meter you must point the meter's one sensor in three directions -- -the x, y and z axis. Then, you combine the three readings in a mathematical equation to calculate the combined field strength. Obviously, its far easier and more accurate to use a 3-axis meter. Triple axis Gauss meters are quite accurate, but they are also more expensive.

Another thing to watch out for when purchasing or renting a Gauss meter is whether or not it is frequency weighted. Most meters will read the same EMF strength no mater what the frequency.

As the human body appears to be sensitive to both the field strength AND the frequency, Gauss meters used for biological purposes should be "frequency weighted".

This means that if the field is different than 60 Hz the meter will consider the frequency and use it in calculating and displaying the EMF's strength. This feature is why frequency weighted meters will show a higher EMF reading than those meters typically used by electricians and engineers.

Power Lines

An enormous amount of electricity is created at power generating stations and sent across the country through wires that carry high voltages. All power lines radiate electromagnetic fields. The question is: how much are the

power lines near YOUR home radiating? The amount of EMFs coming from a power line depends on its particular configuration. Power companies know which power line configurations are best for reducing EMFs but most don't feel the evidence supports costly changes in the way they deliver electricity.


A substation is an assemblage of circuit breakers, disconnecting switches and transformers designed to substations have been blamed for causing cancer clusters among nearby residents. Paul Brodeur wrote about several such cancer clusters in the July 9, 1990 issue of the New Yorker Magazine.


A key component of a utility's electrical distribution network depends upon numerous, small transformers mounted on power poles. A transformer looks like a small metal trash can, usually cylindrical.

Even when the electrical service is underground, you will often see a metal box (usually square} located on the ground near the street. Many people don't realize that when they see a transformer, the power line feeding the transformer is 4000 to 13,800 volts.

The transformer then reduces the voltage to the 120/240 volts needed by nearby homes. Since these transformers can be seen in almost every neighborhood, they are a source of concern.

EMFs near a transformer can be quite high, but due to its small structure, the field strength diminishes rapidly with distance, as it does from any point source. For this reason, having a transformer located near your home is usually not a major source of concern, although just to make sure, everyone should measure the field strength around it.

Home Wiring

If your home has high EMF readings, it is important to determine the sources of the EMF so that remedial action can be taken, if possible. Many times a particular room will have a higher EMF reading. Check to see if the electricity is coming into the house on the wall outside that room. When this is the case, it is usually a good idea to block off that room and only use it for storage purposes.

Sometimes, the source of a high magnetic field is incorrect wiring. If you suspect that your home is wired improperly, obtain the services of a licensed electrician. Warning: Do not touch electric wires, even if you think the current is turned off. If you need to disconnect electrical circuits to determine the source of magnetic fields, you should call a licensed electrician.


Computers are a complicated subject. Know this: EMFs radiate from all sides of the computer. Thus, you must not only be concerned with sitting in front of the monitor but also if you are sitting near a computer or if a computer is operating in a nearby room.

The Swedish safety standard, effective 711/90, specifies a maximum of 0.25 mG at 50 cm from the display. Many US manufactured computers have EMFs of 5 - 100 mG at this distance. And know this too: the screens placed over monitors do NOT block EMFs. Not even a lead screen will block ELF and VLF magnetic fields.

Space does not permit a more thorough discussion of computers. If you use a computer, it is important that you

measure your EMF exposure with a Gauss meter and review the literature concerning the health impacts of computer use.

Electric Blankets and Waterbeds

Electric blankets create a magnetic field that penetrates about 6-7 inches into the body. Thus it is not surprising that an epidemiological study has linked electric blankets with miscarriages and childhood leukemia.

This pioneering work was performed by Dr. Nancy Wertheimer and Ed Leeper, who originally discovered that magnetic fields were linked to childhood leukemia. Similar health effects have been noted with users of many electric blankets and waterbed heaters will emit EMFs even when turned off.

The devices must be unplugged to delete the EMF exposure Additionally, there is the issue regarding the vibrations that are generated by sleeping on standing water. There is less hard data in this area but some experts are concerned about the consequences.

Electric Clocks

Electric clocks have a very high magnetic field, as much as 5 to 10 mG up to three feet away. If you are using a bedside clock, you are probably sleeping in an EMF equivalent to that of a powerline Studies have linked high rates of brain tumors with chronic exposure to magnetic fields, so it is wise to place all clocks and other electrical devices (such as telephones and answering devices) at least 6 feet from your bed.

Fluorescent Lights

Fluorescent lights produce much more EMFs than incandescent bulbs. A typical fluorescent lamp of a office

ceiling have readings of 160 to 200 mg 1 inch away.

Microwave Ovens and Radar

Microwave ovens and radar from military installations and airports emit two types of radiation -- microwave and ELF. Microwaves are measured in milliwatt per centimeter squared (mW/cm2) As of 1/1/93, the U.S. safety limit for microwave exposure is 1 mW/cm2, down from a previous 10 mW/cm2. The Russian safety limit is .01 mW/cm2. All microwave ovens leak and exceed the Russian safety limit. In addition, recent Russian studies have shown that normal microwave cooking coverts food protein molecules into carcinogenic substances.

When measuring microwaves from military and airport radar sources, 100% accurate readings can only be found with extremely expensive digital peak-hold meters. Why? Because analog devices begin to drop their reading immediately after the radar sweep passes. Thus, while an analog meter can show whether or not you are being exposed to radar EMFs, analog meters can't show your true exposure. Although thousands of dollars to purchase, digital-hold meters capable of accurately detecting radar EMFs can be rented for several hundred to over a thousand dollars per month.

Telephones and Answering Machines

Telephones can emit surprisingly strong EMFs, especially from the handset. This is a problem because we hold the telephone so close to our head. Place the Gauss meter right against the ear piece and the mouth piece before buying a phone.

Some brands emit no measurable fields and others emit strong fields that travel several inches....right into your brain. Answering machines, particular those with adapter plugs (mini-transformers), give off high levels of EMFs.

Electric Razors and Hair Dryers

Electric razors and hair dryers emit EMFs as high as 200 to 400 mG. This seems alarming, but we don't know if this is worse (or better) than a chronic exposure to a 2-3 mG field. Some EMF consultants recommend that hair dryers not be used on children as the high fields are held close to their rapidly developing brain and nervous system.

Prudent Avoidance

Electricity is an inseparable part of our modern day society. This means that EMFs will continue to be all around us. But as Discover Magazine postulated, aside from making our life easier, is electricity also making our lives shorter?

Most experts agree that limited, non-chronic exposure to EMFs is not a threat. For example, it is probably acceptable for a person to be near a toaster in the morning.

BUT, it is not advisable for a person to sleep under an electric blanket, up close, live near a powerline/substation, and sleep in a room where the power enters the home. This person is under an extreme case of chronic exposure. This condition, unfortunately, applies to millions of Americans.

If you wish to follows the EPA's advice and practice "prudent avoidance" then the following advice is offered:

Measure your home, work and school environments with a Gauss meter Measure EMFs both inside and outside your home. Don't let your children play near power lines, transformers, radar domes and microwave towers.

Avoid areas where the field is above 1 mG. Measure the EMFs from appliances both when they are operating and when they are turned off. Some appliances (like TVs) are still drawing current even when they are off.

Don't sleep under an electric blanket or on a waterbed. If you insist on using these, unplug them before going to bed (don't just turn it off). Even though there is no magnetic field when they are turned off, there may still be a high electric field.

Don't sit too close to your TV set. Distance yourself at least 6 feet away. Use a Gauss meter to help you decide where it is safe to sit.

Rearrange your office and home area so that you are not exposed to EMFs from the sides/backs of electric appliances and computers. In the home, it is best that all major electrical appliances, such as computers, TVs, refrigerators etc, be placed up against outside walls. That way you are not creating an EMF field in the adjoining room.

Don't sit too close to your computer. Computer monitors vary greatly in the strength of their EMFs, so you should check yours with a meter. Don't stand close to your microwave oven. Move all electrical appliances at least 6 feet from your bed. Eliminate wires running under your bed. Eliminate dimmers and 3-way switches.

Be wary of cordless appliances such as electric toothbrushes and razors. You may choose not to wear a quartz-analog watch because it radiates pulsating EMFs along your acupuncture meridians.

An older mechanical windup watch would be an acceptable alternative. It is also recommended to wear as little jewelry as possible and to take it off at night. Many people have metal sensitivity which can be aggravated by placing it right on the skin. Measure with a gauss meter to be sure.

And last, but not least, always always always remember that EMFs pass right through walls. The EMF you are reading on your Gauss meter could be radiating from the next room...or from outside your home.

Additional Radiation Info:

Eyeglass frames should ideally be made from plastic with no wires in them, otherwise they can serve as an antenna to focus the radio and cellular phone waves directly into your brain.

What EMF Level Is Safe?

There's a heated debate as to what electromagnetic field (EMF) level is considered safe. Since the experts have not come to an consensus, you'll have to decide for yourself... Many government and utility documents report the usual ambient level of 60-Hz magnetic field to be 0.5 mG.

Thus, any reading higher than 0.5 mG is above the "usual" ambient exposure. Many experts and public officials, as well as the few governments that have made an effort to offer public protection, have adopted the 3 mG cutoff point. The EPA has proposed a safety standard of 1 mG. Sweden has set a maximum safety limit of 1 mG.

Dr. Robert Becker, an MD who has been studying the effects of EMFs for 20 years, states a lmG safety limit in his book Cross Currents. When electricians try to solve a magnetic field problem they do their best to drop the level to 1 mG or below.

Dr. Nancy Wertheimer, a Ph.D. epidemiologist who has been studying EMFs for 20 years, has been looking at the epidemiological data in a different way -- she is trying to associate EMF levels with

health rather than disease. The level she is coming up with is a cut off of 1 mG. Russian researchers claim that 1/1000ths of a mG should be the standard.

The BioElectric Body believes that there are several stages of health between "optimum wellness", "degenerative disease" and "Cancer". Thus, we maintain our own living and sleeping quarters at 0.5mG and below.


Infrared Thermometer

How do I use my infrared thermometer?

While there are many different shapes and styles of handheld infrared thermometers, and many features available, the basic function is very similar in very nearly every variation. The first step in taking a measurement, is determining the desired target. All portable infrared laser thermometers regardless of design will have a means of "aiming" the instrument at the target. Some versions simply are shaped in such a way that pointing at the target is the targeting method. Others have a guide such as a laser spot, or group of laser spots that indicate the area being targeted. The temperature measurement is taken when the "trigger" is activated. This is usually a button located either underneath the pyrometer (gun style), or on top (television remote control style). The accuracy of the measurement depends on several factors. See What is the distance to spot ratio? to understand the elements governing accuracy.

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How do infrared thermometers work?

All matter- liquid, solid, or gas--constantly exchanges thermal energy in the form of electromagnetic radiation with its surroundings. If there is a temperature difference between the object in question and its surroundings, there will be a net energy transfer in the form of heat. This means that a colder object will be warmed at the expense of its surroundings, and a warmer object cooled. If the object in question is at the same temperature as its surrounding, the net radiation energy exchange will be zero. In either case, the characteristic spectrum of the radiation depends on the object and its surroundings' absolute temperatures which is a relative to absolute zero (0 K, –273.16°C, –459.69°F). Infrared thermometers take advantage of this "radiation dependence" on temperature to produce a value for the targeted object and displays the results for the operator to read.

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What is the distance to spot ratio?

D/S Ratio- Distance to Spot ratio refers to a very important feature of your infrared thermometer. This ratio is the size of the area being evaluated by the infrared thermometer as it relates to distance. In other words, the area being measured becomes larger as the distance increases. This has a profound impact on the accuracy or precision of the reading. If the target you are measuring is 6 inches in size, and your infrared thermometer has a D/S ratio of 8:1, than the maximum distance you can reliably measure the temperature of the target is 48 inches. Beyond this distance, not only is the target being measured, but whatever else falls within the "spot" is being measured as well. This means that if a very hot object is the target, and it is in cooler surroundings, than measurements taken beyond the maximum distance will include cooler elements, and lowering the "average" of what is in the "spot".

D/S Ratio X Target Size, or 8:1 X 6 = maximum measure distance of 48 inches.

As the target size decreases, or the distance to the target increases, a larger D/S Ratio becomes necessary. Using the same example above, and changing first the target size, and then the D/S ratio, you can see that this formula helps you decide the correct D/S ratio and therefore the Infrared Thermometer for your needs.

D/S Ratio X Target Size, or 8:1 X 2 = maximum measure distance of 16 inches.

D/S Ratio X Target Size, or 12:1 X 2 = maximum measure distance of 24 inches.

D/S Ratios vary greatly, so carefully compare this feature of IR Thermometers when comparison shopping. This ratio, and temperature range are the two biggest factors to consider when shopping for an Infrared Thermometer!

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What are some common household applications for infrared thermometers?

While infrared thermometers are primarily used in industry, there as several useful applications for around the home!

Heating and cooling efficiency- This is a popular use for those who live in extreme climate areas. Very cold winters, or very hot summers mean that escaping heating or cooling drives up the electric bill!. During the extreme weather time of the year, the user can locate escaping heat, or cold around windows and doors and dramatically improve the heating, or cooling efficiency of their home! Even a reasonably small area around a window or two that you can seal, may well return your investment in your thermometer in a single season by reducing heating or cooling costs!

Electrical Troubleshooting- A troublesome circuit breaker "popping" frequently, can be an indication of loose connections within the electrical box. The qualified do-it-yourselfer can easily locate a loose connection by "scanning" through the electrical box. Overall, the contents of the box should be within a temperature "range", but any loose connections will be drawing additional amperage and causing extra heating as a result. Of course, as always when dealing with electricity, only qualified persons should make corrections, and only after taking the necessary precautions.

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What are some common industrial applications for infrared thermometers?

There are literally hundreds of applications in industry for infrared thermometers. Some uses would not occur to the average person. Here is a list of some common applications, and a few unusual ones as well!

HVAC- Heating Ventilation and Air Conditioning Technicians are one of the most frequent users of portable infrared thermometers. It is vital in their job, to take accurate measurements, usually from a distance to gauge the efficiency of the unit by measuring the degree of cooling (or heating) of the air.

Home Inspections- Home inspectors have many uses as listed in the categories above. They also might use their infrared thermometer to measure hot water temperature, look for insulation leaks etc. This is becoming on of the most popular applications for pyrometers.

Health Inspectors- Perhaps not an example that would occur to everyone, health inspectors closely monitor many temperature related things in and around food handling and preparation. Heating bins and surfaces hot enough? Refrigerators and freezers cold enough to protect food from spoiling? Restaurant owners, does your health inspector use an infrared thermometer? If so, getting the same tool he uses is wise to avoid surprises!

Process Controls- This is a very broad category, but the following list details some industries that utilize handheld infrared thermometers for monitoring and maintaining temperature sensitive aspects of their business. Some examples are:

Measuring the surface temperature of curing concrete to determine if cracking is a danger.

Measuring asphalt prior to pour to ensure smooth application.

Measuring ink temperatures prior to mix for accurate color matching in printing presses.

Monitoring the temperature of lamination materials for proper adhesion

Verifying part temperature following an oven baking operation to ensure proper drying, ductility, curing of paints and coatings etc.

Any application where taking temperature is either impossible through direct contact because of barriers or distance.

Taking temperatures in a hazardous environment where the user can maintain a safe distance by using non contact infrared thermometer technology.

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What should I consider when shopping for an infrared thermometer?

There are many factors to consider when shopping for an infrared thermometer. There are many features and variables available, and of course, a very, very wide range of prices. The following list of factors is structured so that the factors at the top of the list will likely have the greatest impact on cost. You will notice that some of these factors are related in the way that they affect the value of the instrument. So ask your self the following questions before shopping, and use the list below to help guide you in selecting the best infrared thermometer for your needs. You can than start comparison shopping with an arsenal of information that will enable you to get the best value! The one factor not listed below is Warranty from the provider. While shopping, use this to determine what distributor has the greatest confidence in the product they are selling!

Question: What is the minimum and maximum temperature I might expect to be measuring?

Question: What is the maximum distance I may be measuring from?

Question: What is the smallest target object I may need to measure?

Question: How accurate do my results need to be?

Question: Do I need features like, Overtemp. alarm, Logging multiple readings etc.

Question: Do I need a targeting guide like a laser spot for accuracy?

Temperature Range- One of the most important feature that affects the cost of an infrared thermometer is the temperature range of the instrument. A couple of important things to note, is that most thermometers fall into several groups that have a natural separation of costs. Medical Use, Smaller Range, Medium Range, Lower Minimum Medium Range, Wide Range, Very Wide Range.

Obviously an infrared thermometer intended for medical purposes only needs a limited range. There is a much greater need for accuracy however. These are often very inexpensive and intended only for this purpose. A more expensive unit could take measurements in the appropriate range, but the accuracy would likely not qualify, eliminating it as useful for this purpose. Of course, plus or minus 2 degrees F is the difference between normal, and a fever!

Smaller Range infrared thermometers vary somewhat, but generally have a total range of 450 F or so. A typical range for an instrument in this category might be -4F to 425 F. Somewhat lower and higher variations will be noted, but this is an average for this category. Usually inexpensive, and useful for many applications, this group is your choice if this range meets your needs.

Medium Range infrared thermometers typically are more consistent in their grouping regarding min. and max. temperature. The average temperature range for this group is -25F to 999F. This is the group that has the most versatility without adding a great deal of cost in most cases.

Lower Minimum Medium Range infrared thermometers are also sometimes called "Food Service IR Thermometers". This is the case because the lower end of the range reaches down below -40F. (Usually -50F or more) This is important to the food service industry to ensure the safety and freshness of frozen foodstuffs. This is the group most likely used by health inspectors.

Wide Range IR thermometers represent the first big jump in cost. For this reason, the health inspector for example, will likely select the prior category. Number one because of cost, and number two, because he would likely not need the extreme upper range that this unit offers. Although the lower end is the same as the previous group, and the accuracy is the same, the extra cost may not be attractive to that consumer, unless the thermometer will be used in other environments requiring the expanded upper range. Typical ranges for this group go below -50F to 1000+ F.

Very Wide Range infrared thermometers are obviously the most costly group of IR thermometers, if we ignore other features than range alone. Typical temperature ranges for this group can be nearly -60F to 1800+ F! Found mostly in high end industrial applications, these units are rarely found in everyday uses as mentioned above. They are reserved for special applications and as such are priced accordingly!

Conclusion: The better value will be the instrument with the greatest range for the same cost, all other factors being equal.

Distance from the target / target size- These go hand in hand as we look at the Distance to Spot Ratio. This feature is as important as temperature range when accurate readings are needed. See what is the distance to spot ratio. This determines many things among which are, the smallest target you can measure and from what distance. Distance to Spot Ratios (D/S) will vary dramatically, and have an equally dramatic impact on cost. D/S can be as low as 4:1 and as high as 50:1 or more!

Conclusion: The better value will be the instrument with the highest D/S ratio for the same cost, all other factors being equal.

Instrument Accuracy- Accuracy seems to be, on the surface a simple factor. However, if cost is a concern as it generally is, than selecting an infrared thermometer that meets your needs as opposed to exceeding your needs, may mean a reduced cost for a suitable instrument. I always suggest erring on the side of caution, and making sure the accuracy is adequate and then some.

Conclusion: The better value will be the instrument with the greatest accuracy for the same cost, all other factors being equal.

Features- The importance of various features is completely dictated by the intended end use. If simple measurements are all that is required, than data logging, averaging, and high temperature alarms etc. are not necessary. In many cases however, these features may be available for a minor added cost when selecting an upgraded unit, or even the same cost from another brand name! This is where the diligent shopper can ensure that the best infrared thermometer for his or her needs is acquired by visiting several outlets and comparison shopping.

Conclusion: If extra features are needed, the instrument with the best features for the same cost, all other factors being equal will be the greatest value, and most useful.

Laser spots / Targeting Guides- The need for targeting aids such as laser spots or sighting scopes is primarily dictated by the need for accuracy. It is important to note, that recent versions of infrared thermometers available now, almost always have the laser option. The one negative to this feature is that it is a drain on the battery. Many versions have a laser on/off feature, which can be disabled to either achieve extended overall battery life, or preserve remaining life when the battery has been in service for a while and is becoming drained.

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Water Quality

Water quality indicators
Key measures provide a snapshot of conditions

Volunteer monitors conduct water quality tests
Volunteer monitors conduct water quality tests to provide a snapshot of river conditions.

Colorado River Watch Network volunteers test for several key water quality indicators. The resulting water quality data provides baseline information, helps identify trends or changes in water quality over time, and aids scientists investigating problems such as nonpoint-source pollution and nutrient enrichment.

LCRA professional monitors conduct similar tests when they evaluate water quality. The testing supplies a stream of data to LCRA, providing an early warning system for potential sources of water pollution.

These are the key measurements and why they are important water-quality indicators:

  • Dissolved oxygen (DO)
    The DO test measures the amount of oxygen dissolved in the water. Oxygen is essential for both plants and animals, but high levels in water can be harmful to fish and other aquatic organisms. Nonpoint-source pollution can decrease the amount of dissolved oxygen in water. The decomposition of leaf litter, grass clippings, sewage, and runoff from feedlots decreases DO readings. Decreased DO can be harmful to fish and other aquatic organisms. Dissolved oxygen is measured in milligrams per liter (mg/L). Expected levels: 4.0 to 12.0 mg/L

  • Water temperature
    Aquatic organisms are dependent on certain temperature ranges for optimal health. Temperature affects many other parameters in water, including the amount of dissolved oxygen available, the types of plants and animals present, and the susceptibility of organisms to parasites, pollution and disease. Causes of temperature changes in the water include weather conditions, shade and discharges into the water from urban sources or groundwater inflows. Temperature is measured in degrees Celsius (°C). Seasonal trends: May to October: 22 to 35°C, November to April: 2 to 27°C

  • pH
    A pH test measures the alkalinity or acidity concentration in water. A pH of 7 is neutral, below 7 is acidic, and above 7 is basic or alkaline. Acid rain, from auto exhaust or coal-fired power plants, causes a drop in the pH of water. Pollution from accidental spills, agricultural runoff and sewer overflows can also change the pH. Buffering capacity is water's ability to resist changes in pH, and is critical to the survival of aquatic life. The limestone soils of Central Texas act to neutralize these acids and often result in a more basic pH. While young fish and insect larvae are sensitive to a low pH (acid), extreme values on either end of the scale can be lethal to most organisms. Expected levels: 6.5 to 9.0

  • Escherichia coli (E. coli)
    E. coli is a type of fecal coliform bacteria that comes from human and animal waste. The Enivronmental Protection Agency uses E. coli measurements to determine whether fresh water is safe for recreation. Disease-causing bacteria, viruses and protozoans may be present in water that has elevated levels of E. coli. Levels of E. coli can increase during flooding. E. coli is measured in number of colony forming units. The EPA water quality standard for E. coli bacteria is 394 colony forming units per 100 mL.

  • Specific conductance
    The specific conductance test measures the ability of water to pass an electrical current. Conductivity in water is affected by the presence of inorganic dissolved solids such as chloride, sulfate, sodium, calcium and others.

Conductivity in streams and rivers is affected by the geology of the area through which the water flows. Streams that run through granite bedrock will have lower conductivity, and those that flow through limestone and clay soils will have higher conductivity values. High conductance readings can also come from industrial pollution or urban runoff -- water running off of streets buildings, and parking lots. Extended dry periods and low flow conditions also contribute to higher specific conductance readings.
Because an organic compound such as oil does not conduct electrical current very well, an oil spill tends to lower the conductivity of the water. Temperature also affects conductivity; warm water has a higher conductivity. Specific conductance is measured in microsiemens per centimeter (µs / cm). Expected levels: 300 to 700 µs /cm in most of the Colorado River watershed; higher near San Saba and the coast.
  • Nitrates
    Nitrogen is a nutrient necessary for growth of all living organisms. The Colorado River Watch Network monitors test for nitrogen in the form of nitrate (NO3-N). In excess amounts, nitrates in water cause an increase in algae growth. Algae can rob the water of dissolved oxygen and eventually can kill fish and other aquatic life. Sources of nitrates may include human and animal wastes, industrial pollutants and nonpoint-source runoff from heavily fertilized croplands and lawns. Under certain conditions high levels of nitrates (10 mg/L or more) in drinking water can be toxic to humans. High levels of nitrates in drinking water have been linked to serious illness and even death in infants. Nitrates are measured in milligrams per liter (mg/L). Expected levels: less than 1.0mg/L.

  • Visual tests
    Monitors are also asked to record physical observations of the water. Volunteers record the clarity of the water, and the presence of plants and other aquatic life. They may also report the amount of rainfall received in the area.

Using Hioki Data Logger


This is a comprehensive hioki data logger userguide prepared by KKInstruments.  If you have any question, please contact us.


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