A faintly-colored circular arc similar to a rainbow but formed on fog layers containing drops whose diameters are 100 microns or less. Also called mistbow, white rainbow.

A sudden brief increase in the speed of the wind, followed by a lull or slackening. Compare to peak gust.

The length of fluid flow (gas or liquid) past a sensor required for the sensor to respond to 63.2% of a step change in speed. Expressed in feet or meters. For anemometers, this value is calculated from time constant times wind tunnel speed.

A graphical aid used in the reduction of data from a winds aloft observation.

Any soft, gentle breeze.

The number of cycles per second between the limits of a frequency band.

A counterclockwise change in wind direction. Backing winds with height are indicative of cold air advection (CAA).

See hydrologic accounting.

A device that combines several separate communications signals into one and outputs them on a single line.

A thermometer, invented by James Six in 1782, which simultaneously indicates the maximum and minimum temperatures attained during a given interval of time. A U-tube min/max thermometer

February 2nd. In American folklore, a day that is popularly supposed to provide the key to the weather for the remainder of the winter. Specifically, if the ground-hog upon emerging from its hole casts a shadow, it will return underground, thereby forebod ...

An instrument for measuring the frost point of the atmosphere.

A measure, proposed by Angstrom, of the precipitation effectiveness of a region.

Instrument used to measure the amount of water evaporated from the soil surface during a given time interval.

An instrument which measures the instantaneous rate at which rain is falling on a given surface. Also called a rate-of-rainfall gauge.

An instrument used to measure changes in the level of the water in an evaporation pan. The gauge is normally placed in a Stillwell and adjusted so that the point of the hook just breaks the water surface. The change in water level is read on the attached ...

An instrument, located at the surface observing station, which is used to record the data presented by a radiosonde aloft.

The transducer of any hygrometer, i.e. that part of a hygrometer that quantitatively "senses" atmospheric water vapor.

Name sometimes given to a transmissometer.

The lowest level at which the wind becomes geostrophic in the theory of the Ekman spiral. Also called gradient wind level.