Science / Weather Glossary

Disturbance: This has several applications. It can apply to a low or cyclone that is small in size and influence. It can also apply to an area that is exhibiting signs of cyclonic development. It may als . . . View Full Definition

Diurnal: Pertaining to actions or events that occur during a twenty-four hour cycle or recurs every twenty-four hours. Meteorological elements that are measured diurnally include clouds, precipitatio . . . View Full Definition

Divergence: Wind movement that results in a horizontal net outflow of air from a particular region. Divergence at lower levels is associated with a downward movement of air from aloft. Contrast with convergence.

Dog Days: The name given to the very hot summer weather that may persists for four to six weeks between mid-July through early September in the United States. In western Europe, this period may exist . . . View Full Definition

Doldrums: Located between 30 degrees North and 30 degrees South latitudes in the vicinity of the equator, this area typically has calm or light and variable winds. Also a nautical term for the equator . . . View Full Definition

Doppler Radar: Weather radar that measures direction and speed of a moving object, such as drops of precipitation, by determining whether atmospheric motion is horizontally toward or away from the radar. U . . . View Full Definition

Downburst: A severe localized downdraft from a thunderstorm or shower. This outward burst of cool or colder air creates damaging winds at or near the surface. Sometimes the damage resembles tornadic damage.

Downdraft: A sudden descent of cool or cold air to the ground, usually with precipitation, and associated with a thunderstorm or shower.

Downpour: A heavy rain.

Downslope Effect: The warming of an air flow as it descends a hill or mountain slope.

Drainage Wind: A katabatic wind, it is caused by the cooling of air along the slopes of a mountain.

Drifting Snow: Snow particles blown from the ground by the wind to a height of less than six feet.

Drifts: Normally used when referring to snow or sand particles are deposited behind obstacles or irregularities of the surface or driven into piles by the wind.

Drizzle: Slowly falling precipitation in the form of tiny water droplets with diameters less than 0.02 inches or 0.5 millimeters. It falls from stratus clouds and is often associated with low visibil . . . View Full Definition

Dropsonde: A radiosonde dropped with a parachute from an aircraft rather than lifted by a balloon to measure the atmosphere below.

Drought: Abnormal dry weather for a specific area that is sufficiently prolonged for the lack of water to cause serious hydrological imbalance.

Dry Adiabat: The line on a Skew T-Log P chart that depicts the lifting of dry air, or air that is unsaturated. As a parcel rises adiabatically, its pressure decreases and its temperature falls due to the . . . View Full Definition

Dry Bulb Thermometer: A thermometer used to measure the ambient temperature. The temperature recorded is considered identical to air temperature. One of the two thermometers that make up a psychrometer.

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