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ABSOLUTE HUMIDITY
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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.
- ANEMOMETER
- An instrument that
measures the speed or force of the wind.
- ARID
- 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.
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- CALM
- Atmospheric conditions devoid of wind or any other air motion. In
oceanic terms, it is the apparent absence of motion of the water surface
when there is no wind or swell.
- CELSIUS TEMPERATURE SCALE
- 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."
- CLIMATE
- 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.
- CLIMATOLOGY
- The study of climate. It includes climatic data, the analysis of the
causes of the differences in climate, and the application of climatic
data to the solution of specific design or operational problems.
- CLOUDBURST
- A sudden, heavy rainfall of a showery nature. See downburst.
- COOLING DEGREE DAY
- A cooling degree day is given for each degree that the daily mean
temperature departs above the baseline of 75 degrees Fahrenheit. It
is used to estimate the energy requirements, and is an indication of
fuel consumption for air conditioning or refrigeration. Refer to degree
day or heating degree day.
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- DEGREE DAY
- A measure of the departure of the mean daily temperature from a given
standard. That is one degree day for each degree (Fahrenheit or Celsius)
of departure above or below the standard during one day. Refer to cooling
degree day and heating degree day.
- DEW
- 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.
- DEW POINT
- The temperature to which air must be cooled at a constant pressure
to become saturated.
- DOG DAYS
- 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.
- DOWNPOUR
- A heavy rain. See cloudburst.
- DRIZZLE
- Slowly falling precipitation in the form of tiny water droplets with
diameters less than 0.02 inches or 0.5 millimeters. It falls from stratus
clouds and is often associated with low visibility and fog. It is reported
as "DZ" in an observation and on the METAR.
- DROUGHT
- Abnormal dry weather for a specific area that is sufficiently prolonged
for the lack of water to cause serious hydrological imbalance.
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- EL NINO
- 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.
- EVAPORATION
- 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.
- EVAPOTRANSPIRATION
- The total amount of water that is transferred from the earth's surface
to the atmosphere. It is made up of the evaporation of liquid or solid
water plus the transpiration from plants.
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- FAHRENHEIT TEMPERATURE SCALE
- 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.
- FORECAST
- 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.
- FRONT
- The transition zone or interface between two air masses of different
densities, which usually means different temperatures. For example,
the area of convergence between warm, moist air and cool, dry air. See
cold front and warm front.
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- GROWING
SEASON
- Considered the period of the year during which the temperature of
cultivated vegetation remains sufficiently high enough to allow plant
growth. Usually considered the time period between the last killing
frost in the spring and the first killing frost of the autumn. The frost-free
growing season is between the first and last occurrence of 32 degrees
Fahrenheit temperatures in spring and autumn.
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- HEAT
- 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.
- HEAT BALANCE
- The equilibrium which exists on the average between the radiation
received by the earth and atmosphere from the sun and that emitted by
the earth and atmosphere. The balance between heat loss (long wave radiation
from the earth back into the atmosphere) and heat gain (incoming solar
radiation).
- HEAT INDEX
- 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.
- HEATING DEGREE DAY
- One heating degree day is given for each degree that the daily mean
temperature is below 65 degrees Fahrenheit. It is used as an indication
of fuel consumption. Refer to degree day or cooling degree day.
- HUMIDITY
- 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.
- HYDROLOGIC CYCLE
- Often called the water cycle, it is the vertical and horizontal transport
of water in all its states between the earth, the atmosphere, and the
seas.
- HYDROLOGY
- The study of the waters of the earth, especially with relation to
the effects of precipitation and evaporation upon the occurrence and
character of water in streams, lakes, and on or below the land surface.
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- MEAN TEMPERATURE
- The average of temperature readings taken over a specified amount
of time. Often the average of the maximum and minimum temperatures.
- METAR
- Acroymn for METeorological Aerodrome Report. It is the primary observation
code used in the United States to satisfy requirements for reporting
surface meteorological data. Minimum reporting requirments includes
wind, visibility, runway visual range, present weather, sky condition,
temperature, dew point, and altimeter setting.
- METEOROLOGY/METEOROLOGIST
- 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.
- MOISTURE
- Refers to the water vapor content in the atmosphere, or the total
water, liquid, solid or vapor, in a given volume of air.
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- NATIONAL CLIMATIC DATA CENTER
(NCDC)
- The agency that archives climatic data from the National Oceanic and
Atmospheric Administration, as well as other climatological organizations.
For further information, contact the NCDC, located in Asheville, North
Carolina.
- NATIONAL METEOROLOGICAL
CENTER (NMC)
- Now incorporated into the National Centers for Environmental Prediction,
it was the division of the National Weather Service that produced, processed,
handled, and distributed meteorological and oceanographic information
to users throughout the Northern Hemisphere, specifically U.S. governmental
organizations.
- NATIONAL OCEANIC AND ATMOSPHERIC
ADMINISTRATION (NOAA)
- A branch of the U.S. Department of Commerce, it is the parent organization
of the National Weather Service. It promotes global environmental stewardship,
emphasizing atmospheric and marine resources. For further information,
contact the NOAA, located in Silver Spring, Maryland.
- NATIONAL WEATHER SERVICE
(NWS)
- A primary branch of the National Oceanic and Atmospheric Administration,
it is responsible for all aspects of observing and forecasting atmospheric
conditions and their consequences, including severe weather and flood
warnings. For further information, contact the NWS.
- NORMAL
- The recognized standard value of a meteorological element as it has
been averaged in a given location over a fixed number of years. Normals
are concerned with the distribution of data within limits of common
occurrence. The parameters may include temperatures (high, low, and
deviation), pressure, precipitation (rain, snow, etc.), winds (speed
and direction), thunderstorms, amount of clouds, percent relative humidity,
etc.
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- PALMER DROUGHT
INDEX
- A long-term meteorological drought severity index produced by the
NOAA/USDA (Department of Agriculture) Joint Agricultural Weather Facility.
The index depicts prolonged times, as in months or years, of abnormal
dryness or wetness. It responds slowly, changing little from week to
week, and reflects long-term moisture runoff, recharge, and deep percolation,
as well as evapotranspiration.
- PRECIPITATION
- 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.
- PREVAILING WIND
- A wind that blows from one direction more frequently than any other
during a given period, such as a day, month, season, or year.
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- RAIN
- 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.
- RAINFALL
- The amount of precipitation of any type, primarily liquid. It is usually
the amount that is measured by a rain gauge. Refer to rain for rates
of intensity and the quantitative precipitation for forecasting.
- RAIN GAUGE
- An instrument used to measure the amount of rain that has fallen.
Measurement is done in hundredths of inches (0.01").
- RELATIVE HUMIDITY
- 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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- SATURATE
- 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.
- SATURATION POINT
- The point when the water vapor in the atmosphere is at its maximum
level for the existing temperature.
- SEASON
- A division of the year according to some regularly recurring phenomena,
usually astronomical or climatic. For example, in the Northern Hemisphere,
winter is said to begin on the winter solstice and end on the vernal
equinox when spring begins, covering the months of December, January,
and February. In the tropics, there is the dry and the rainy season,
depending on the amount of precipitation.
- SEVERE THUNDERSTORM
- A thunderstorm with winds measuring 50 knots (58 mph) or greater,
3/4 inch hail or larger, or tornadoes. Severe thunderstorms may also
produce torrential rain and frequent lightning. See a supercell for
an example.
- SHOWER
- 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.
- SPECIFIC HUMIDITY
- The ratio of the density of the water vapor to the density of the
air, a mix of dry air and water vapor. It is expressed in grams per
gram or in grams per kilograms. The specific humidity of an air parcel
remains constant unless water vapor is added to or taken from the parcel.
- STORM PREDICTION CENTER
- (SPC) A branch of the National Centers for Environmental Prediction,
the Center monitors and forecasts severe and non-severe thunderstorms,
tornadoes, and other hazardous weather phenomena across the United States.
Formerly known as the Severe Local Storms (SELS) unit of the National
Severe Storms Forecast Center. For further information, contact the
SPC, located in Norman, Oklahoma.
- SUPERCELL
- A severe thunderstorm characterized by a rotating, long-lived, intense
updraft. Although not very common, they produce a relatively large amount
of severe weather, in particular, extremely large hail, damaging straight-line
winds, and practically all violent tornadoes.
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- TEMPERATURE
- 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.
- TRANSPIRATION
- The process by which water in plants is transferred as water vapor
to the atmosphere. Refer to evapotranspiration.
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- WEATHER
- 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.
Go
to The Weather Channel
for a more in-depth glossary.
Information
added 5/7/99
UGA CAES Drought Information
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