Any and all forms of water particles, liquid or solid, that fall from the atmosphere and reach the ground.

The unit of speed in the nautical system; one nautical mile per hour. It is equal to 1.1508 statute miles per hour or 0.5144 meters per second.

A liquid-in-glass or liquid-in-metal thermometer using mercury as the liquid.

Infrared radiation emitted by or being propagated through the atmosphere.

A vent used with pressure sensors to reduce the effect of wind on the pressure inlet. It is normally mounted remotely and connected to the sensor using airtight tubing.

Automated Weather Observing Station. A self-contained weather station designed to make aviation weather observations without operator involvement.

Wind with a speed between 28 and 33 knots (32 and 38 mph); Beaufort scale number 7.

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

A momentary decrease in the speed of the wind.

Thermometer for measuring the temperature in the soil at different depths.

A buoyant balloon kept from rising freely by means of a line secured to a point on the ground, as opposed to a free balloon. See kytoon.

The play or loose motion in an instrument due to the clearance existing between mechanically contacting parts.

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

A magnetometer of the electromagnetic type which is used to measure the horizontal intensity of the earth's magnetic field.

An instrument for measuring temperature by utilizing the variation of the physical properties of substances according to their thermal states. Thermometers may be classified into types according to their construction; deformation thermometer, electrical t ...

A unit of pressure which directly expresses the force exerted by the atmosphere. Equal to 1000 dynes/cm2 or 100 pascals.

Ragged low clouds, usually stratus fractus. Most often applied when such clouds are moving rapidly beneath a layer of nimbostratus.

A hypothetical body which absorbs some constant fraction, between zero and one, of all electromagnetic radiation incident upon it, which fraction is the absorptivity and is independent of wavelength. Compare to black body, white body.

The atmospheric pressure computed using station elevation as the reference datum level. Station pressure is usually the base value from which sea level pressure and altimeter setting are determined.

An instrument for recording global solar radiation.