Old snow that has become granular and compacted as a result of melting and refreezing.

See ceilometer.

An aviation weather forecast for a specific flight.

A type of recording siphon barometer. The mechanically magnified motion of a float resting on the lower mercury surface is used to record atmospheric pressure on a rotating drum.

A class of rain gauge in which the level of the collected rain water is measured by the position of a float resting on the surface of the water.

An evaporation pan in which the evaporation is measured from water in a pan floating in a larger body of water.

Overflowing by water of the normal confines of a stream or other body of water, or accumulation of water by drainage over areas which are not normally submerged.

That stage, on a fixed river gauge, at which overflow of the natural banks of the stream begins to cause damage in any portion of the reach for which the gauge is used as an index.

The total amount of water transferred to the atmosphere by evapotranspiration.

A warm, dry wind on the lee side of a mountain range, the warmth and dryness due to adiabatic compression upon descent.

A hydrometeor consisting of a visible aggregate of minute water droplets suspended in the atmosphere near the earth's surface. Fog differs from cloud only in that the base of fog is at the earth's surface while clouds are above the surface.

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.

See foehn.

A unit of illuminance or illumination equal to one lumen per foot'. This is the illuminance provided by a light source of one candle at a distance of one foot.

A unit of energy equal to 1.356joules.

A unit of luminance or brightness equal to 1/d candles per foot'.

A scale of yellows, greens, and blues for recording the color of sea water, as seen against the white background of a Secchi disk.

A type of cistern barometer in which the level of mercury in the cistern is adjusted to the zero point of the scale before each reading.

A buoyant balloon rising freely in the atmosphere, as opposed to a captive balloon.

The actual lifting force of an inflated balloon, usually expressed in grams.