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.

A strong, dangerous, katabatic wind that descends from the mountains into the Palouse River valley in northern Idaho and eastern Washington. Also call a Cow-Killer.

A volume of air small enough to contain uniform distribution of its meteorological properties and large enough to remain relatively self-contained and respond to all meteorological processes.

The scientific name for sun dogs. Either of two colored luminous spots that appear at roughly 22 degrees on both sides of the sun at the same elevation. They are caused by the refraction of sunlight passing through ice crystals. They are most commonly seen during winter in the middle latitudes and are exclusively associated with cirriform clouds. They are also known as mock suns.

Denotes that 1/8th or more of the sky, but not all of the sky, is hidden by any surface-based phenomena in the atmosphere, excluding precipitation. It often reduces horizontal visibility but not the vertical. It is reported as "-X" in an observation and on the METAR. See an obscuration.

The state of the weather when the clouds are conspicuously present, but do not completely dull the sky or the day at any moment. The National Weather Service does not have an amount of sky cover for this condition. Refer to clear, few, scattered, broken, and overcast.

The unit of pressure produced when one newton acts on about one square meter.

When an external pressure is applied to any confined fluid at rest, the pressure is increased at every point in the fluid by the amount of external pressure applied. It means that the pressure of the atmosphere is exerted not only downward on the surface of an object, but also in all directions against a surface which is exposed to the atmosphere. Formulated by Blaise Pascal (1623-1662), a French mathematician, theologian, and physicist.

The highest instantaneous wind speed observed or recorded.

The point nearest the earth on the moon's orbit. This term can be applied to any other body orbiting the earth, such as satellites. It is the opposite of apogee.

The point of the earth's orbit that is nearest to the sun. Although the position is part of a 21,000 year cycle, currently it occurs around January, when the earth is about 3 million miles closer to the sun than at aphelion. This term can be applied to any other celestial body in orbit around the sun. It is the opposite of aphelion.

Any of a number of atmospheric phenomena which appear as luminous patterns in the sky. They do not directly cause adverse weather. They include halos, coronas, rainbows, and fogbows.

The intensely bright portion of the sun visible to the unaided eye; the "surface" of the sun. Reaching temperatures estimated at about 11,000 degrees Fahrenheit, it is the portion of the sun's atmosphere which emits continuous electromagnetic radiation.

A small balloon whose ascent is used to determine the direction and speed of low level atmospheric winds. Also known as a pibal.

A report of in-flight weather by an aircraft pilot or crew member. Often referred to as a PIREP.

Also known as a PPI Scope, it is a radar indicator scope displaying range and azimuth of targets in polar coordinates.

The spreading downdraft and strong straight-line winds preceding a thunderstorm. So called in the American Midwest because of its ability to flatten tall grasses as it passes. See first gust.

The poles are the geographic point at 90 degrees latitude North and South on the earth's surface. They are equal distance from the equator. The polar region is considered to be that area between 60 and 90 degrees latitude, both North and South.

An air mass that forms over a high latitude region. Continental polar air (cP) is formed over cold surface regions and is typically very stable with low moisture. Maritime polar air (mP), produced over warmer waters, is less stable with high moisture.

A semi-continuous, semi-permanent boundary between polar air masses and tropical air masses. An integral part of an early meteorological theory known as the Polar Front Theory.

Marked by a concentration of isotherms and strong vertical shear, this jet is the boundary between the polar air and the subtropical air. It often divides into two branches, the north and the south, and marks the high speed core of the prevailing westerlies. It is associated with the location and motion of the high and low pressure areas of the middle latitudes, and therefore, is variable in position, elevation, and wind speed. Its position tends to migrate south in the Northern Hemispheric winter and north in the summer, and its core winds increase during the winter and become less strong in the summer.

A satellite whose orbit passes over both of the earth's between poles. Compare with a geostationary satellite.

Particles, gases, or liquid aerosols in the atmosphere which have an undesirable effect on man or his surroundings. Something unfavorable to health and life that has been added to the environment.

The rotation of the atmosphere advects higher values of vorticity into an area. This is created by cyclonic turning and is often associated with upward motion of air. When found in advance of a short wave aloft, it often enhances thunderstorm potential. Contrast with negative vorticity advection.

A unit for measuring pressure. One PSI equals the pressure resulting from a force of one pound force acting over an area of one square inch.

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 line of thunderstorms that precedes an advancing cold front. Refer to a squall line.

An elongated area of relatively low pressure preceding a cold front that is usually associated with a shift in wind direction. Refer to a trough.

The force per unit area exerted by the weight of the atmosphere above a point on or above the earth's surface. Also known as atmospheric pressure or barometric pressure.

An aneroid barometer calibrated to indicate altitude in feet instead of unit of pressure. It read accurately only in a standard atmosphere and when the correct altimeter setting is used.

The altitude in standard atmosphere at which a given pressure will be observed. It is the indicated altitude of a pressure altimeter at an altitude setting of 29.92 inches of mercury, and is therefore the indicated altitude above the 29.92 constant pressure surface.

The net difference between the barometric pressure at the beginning and ending of a specified interval of time, usually the three hour period preceding an observation.

The pattern of the pressure change during the specified period of time, usually the three hour period preceding an observation. This is recorded in three categories: falling, rising, or steady.

The amount of pressure change that occurs over a fixed distance at a fixed altitude.

A sudden increase in the observed atmospheric pressure or station pressure.

The pressure characteristic and amount of pressure change during a specified time period, usually the three hour period preceding the observation.

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

It is considered representative of visibility conditions at the observation station. It is the greatest distance that can be seen throughout at least half the horizon circle, but not necessarily continuous.

A type of Doppler radar that measures both wind speed and direction from 1,500 feet up through 55,000 feet in the atmosphere.

A chart of forecast predictions that may include pressure, fronts, precipitation, temperature, and other meteorological elements. Also known as a prog.

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.

A very short duration of time. In regard to a radar, it is a brief burst of a electromagnetic radiation emitted by the radar.