The attenuation of light.

A wind blowing in a direction opposite to the heading of a moving object, thus opposing the object's intended progress; the opposite of a tailwind.

See radiosonde commutator.

The height at which the maximum wind speed occurs, determined in a winds-aloft observation.

Any emission of light at temperatures below that required for incandescence.

A line drawn through geographical points having the same pluvial index.

Frozen or partly frozen rain.

A general term to designate apparatus designed to observe the details of weather during thunderstorms.

Downward-facing pyranometer used for measuring reflected solar radiation.

Same as photometer.

A type of cyanometer. an instrument used to measure the blueness of the sky. The Linke-scale is simply a set of eight cards of different standardized shades of blue. They are evenly numbered 2 to 26. The odd numbers are used by the observer if he or she j ...

A subtle, diumal component of the wind velocity leading to a diumal shift of the wind or turning of the wind with the sun, produced bv the east-to-west progression of daytime surface heating.

Wind with a speed between 22 and 27 knots (25 and 31 mph); Beaufort scale number 6.

A type of wind vane having a split or V-shaped tail. The apex orients itself to the direction of the wind.

A form of psychrometer with wet-bulb and dry-bulb thermometers mounted on opposite sides of a specialty designed graph of the psychrometric tables. It is so arranged that the intersections of two curves determined by the wet-bulb and dry-bulb readings -yi ...

See ceilometer.

The rising of cold water from the deeper areas of the ocean to the surface. This phenomena often occurs along the California coast during the spring and summer.

The total luminous flux received on a unit area of a given real or imaginary surface, expressed in such units as the foot-candle, lux, or phot.

The upward force produced by the gas in a balloon. It is equal to the free lift plus the weight of the balloon and the attached equipment.

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).