Science / Weather Glossary

Gustnado: A weak, and usually short-lived, tornado that forms along the gust front of a thunderstorm, appearing as a temporary dust whirl or debris cloud.

Haboob: Sudanese name for duststorm or sandstorm with strong winds that carry small particles of dirt or sand into the air, particularly severe in areas of drought.

Hail: Precipitation that originates in convective clouds, such as cumulonimbus, in the form of balls or irregular pieces of ice, which comes in different shapes and sizes. Hail is considered to ha . . . View Full Definition

Halo: The ring of light that seems to encircle the sun or moon when veiled by cirrus clouds. To produce this phenomena, the ice crystals must be in a heterogeneous arrangement to refract the sunli . . . View Full Definition

Haze: A suspension of fine dust and/or smoke particles in the air. Invisible to the naked eye, the particles reduce visibility by being sufficiently numerous to give the air an opalescent appearan . . . View Full Definition

Heat: A form of energy transferred between two systems by virtue of a difference in temperature. The first law of thermodynamics demonstrated that the heat absorbed by a system may be used by the . . . View Full Definition

Heat Balance: The equilibrium which exists on the average between the radiation received by the earth and atmosphere from the sun and that emitted by the earth and atmosphere. The balance between heat los . . . View Full Definition

Heat Exhaustion: The effect of excessive heat, particularly when combined with high humidity, on a human being. Signs of heat exhaustion include a general weakness, heavy sweating and clammy skin, dizziness . . . View Full Definition

Heat Index: The combination of air temperature and humidity that gives a description of how the temperature feels. This is not the actual air temperature.

Heat Lightning: Lightning that appears as a glowing flash on the horizon. It is actually lightning occurring in distant thunderstorms, just over the horizon and too far away for thunder to be heard.

Heat Stroke: Introduced to the body by overexposure to high temperatures, particularly when accompanied by high humidity. The signs of heat stroke include when an individual's body temperature is greater . . . View Full Definition

Heat Wave: A period of abnormally and uncomfortably hot weather. It could last from several days to several weeks. The Weather Channel uses the following criteria for a heat wave: a minimum of ten stat . . . View Full Definition

Heating Degree Day: One heating degree day is given for each degree that the daily mean temperature is below 65°F. It is used as an indication of fuel consumption.

Helicity: A property of a moving fluid, such as air, representing the potential for helical flow (flow that follows a corkscrew pattern). Computed from the vertical wind profile of the lower atmospher . . . View Full Definition

High Clouds: A term used to signify cirriform clouds that are composed of ice crystals and generally have bases above 20,000 feet. The main types of high clouds are cirrus,cirrocumulus, and cirrostratus. . . . View Full Definition

High Latitudes: The latitude belt roughly between 60° and 90° North and South.

High Pressure System: An area of relative pressure maximum that has diverging winds and a rotation opposite to the earth's rotation. This is clockwise the in Northern Hemisphere and counterclockwise in the Southe . . . View Full Definition

Hoarfrost: Another name for frost. A deposit of hoarfrost occurs when air with a dew point below freezing is brought to saturation by cooling.

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