Wind with a speed between 4 and 27 knots (4 and 31 mph); Beaufort scale numbers 2 through 6.

A type of atmometer. It is a pan used in the measurement of the evaporation of water into the atmosphere. The NWS Class A pan is a cylindrical container 48 inches in diameter and 10 inches deep.

Any one of six gases, helium, neon, argon, krypton, xenon, and radon, all of whose shells of planetary electrons contain stable numbers of electrons such that the atoms are chemically inactive.

Navy Operational Global Atmospheric Prediction System. A global meteorological model operated by the Department of Defense.

In a system of moist air, the dimensionless ratio of the mass of water vapor to the total mass of the system.

The total infrared radiation emitted from the earth's surface. To be carefully distinguished from atmospheric radiation, effective terrestrial radiation, and insolation.

The maximum rate at which precipitation can pass through the surface into the soil, for a given soil in a given condition.

Graduated fixed stake used in regions of abundant snowfall to facilitate the measurement of snow depth.

The difference between the outgoing infrared terrestrial radiation of the earth's surface and the downcoming infrared counterradiation from the atmosphere.

Operation mode of a communication circuit in which one end can only transmit and the other end can only receive.

The total area drained by a river and its tributaries. Same as river basin.

A recording anemoclinometer.

An instrument which records the duration of sunshine and gives a quantitative measure of the amount of sunshine by the action of the sun's rays upon blueprint paper. A type of sunshine recorder.

A thin metal disc partially evacuated of air used to measure atmospheric pressure by measuring its expansion and contraction.

A wind blowing in the same direction as the heading of a moving object. thus assisting the object's intended progress. The opposite of a head wind.

See constant-level balloon.

Forecasting weather by the use of numerical models, run on high speed computers. Most of the NWP for the National Weather Service is done at the National Centers for Environmental Prediction (NCEP).

A radiosonde which is dropped by parachute from an aircraft for the purpose of obtaining soundings of the atmosphere below.

An instrument for determining the degree of polarization of light. See photopolarimeter.

A strong wind characterized by a sudden onset, a duration on the order of minutes, and a rather sudden decrease in speed.