Warm Conveyor Belt: A band of warm moist air drawn into the flow around a trough or low; it rises above a frontal surface and forms cloud and rain along and ahead of the front.

Warm-Core Low: A low-pressure area that is warmer at its center than at its periphery. Tropical cyclones exhibit this temperature pattern.

Warm Front: A front which moves so that cold air is replaced by warm air.

Warm-Front Wave: A small depression which starts as a wave on the warm front and moves away from the parent low.

Warm Occlusion: See Occluded front.

Warm Sector: The sector of a depression, usually triangular in shape, which contains the warmest air. It is bounded by warm and cold fronts and grows narrower as the cold front overtakes the warm during the process of Occlusion.

Warm-Type Occluded Front: A front that forms when the air behind the cold front is warmer than the air underlying the warm front it is overtaking.

Water Equivalent: The depth of water that would result from the melting of a snow sample. Typically about 10 inches of snow will melt to 1 inch of water, producing a water equivalent of 10 to 1.

Water Hemisphere: A term used to refer to the Southern Hemisphere, where the oceans cover 81% of the surface (compared to 61% in the Northern Hemisphere)!

Waterspout: A very rapidly rotating funnel-shaped cloud extending down from the base of a Cb to the sea, where it creates a disturbance. It is the marine equivalent of a tornado.

Water Vapor: Water in the form of an invisible vapor; the gas formed when water is evaporated.

Wave Clouds: Clouds which form where air rises in the crests of waves, often but not invariably associated with airflow across mountains.

Wave Cyclone (Mid-Latitude Cyclone): An extratropical cyclone that forms and moves along a front. The circulation of winds about the cyclone tends to produce a wavelike deformation on the front. An appreciation for the energy of a wave cyclone can be realized by recognizing the fact that an average wave cyclone dumps at least 200,000,000,000,000 (200 trillion) pounds of water on Earth's surface during its lifetime of several days! As a little side note: A wave cyclone in March of 1776 forced the British to cancel a massive amphibious assault at Dorchester heights, south of Boston, where General Washington held a well-fortified position. The storm kept Dorchester heights from becoming a bloody, historic battlefield, such as Lexington, Concord, and Bunker Hill!

Wave Depression: A depression which forms at the tip of a wave-like undulation on a front.

Wavelength: The distance between successive wave crests.

Wave Motion: Oscillatory movement in any medium which results in waves moving through it.

Wave Number: Either the number of waves in unit distance (the reciprocal of the wavelength) or 2 pi times this number.

Weather: The condition of the atmosphere at any particular time and place. But you already knew that!

Weather Analysis: The stage prior to developing a weather forecast. This stage involves collecting, compiling, and transmitting observational data.

Weather Elements: The elements of air temperature, air pressure, humidity, clouds, precipitation, visibility, and wind that determine the present state of the atmosphere, the weather.

Weather Forecasting: Predicting the future state of the atmosphere. Back in the old days, due to extremely limited availability of accurate weather reports and forecasts, the average life expectancy for an airmail pilot between 1918 and 1925 was about 4 years! The USA's first official weather forecaster was Professor Increase A. Lapham, who began making predictions for the US Weather Service on November 8, 1870!

Weather Modification: Deliberate human intervention to influence and "improve" atmospheric processes. [scare quotes emphasized]

Weather Type Forecasting: A forecasting method where weather patterns are categorized into similar groups or types.

Weather Types: Certain weather patterns categorized into similar groups. Used as an aid in weather prediction.

Weather Warning: A forecast indicating that hazardous weather is either imminent or actually occurring within the specified forecast area.

Wedge of High Pressure: Another term for a ridge.

Wegener Arcs: An extensive set of arcs, touching the 22 deg. upper tangent arc over the sun, curving past the zenith, and crossing each other and the parhelic circle in the anthelion (the point on the circle opposite the sun). They are a very rare occurrence. The arcs are due to light being refracted and internally reflected in horizontally oriented, pencil-shaped, hexagonal ice-crystals.

Weighting Gage: A recording precipitation gage consisting of a cylinder that rests on a spring balance.

Wendy Windblows: The punning name given to a network of automatic weather stations on hilltops in England and Wales sponsored by hang-glider pilots. subscribers are given code numbers to interrogate the reports by telephone.

Westerlies: See Prevailing Westerlies.

Wet Adiabatic Rate: Another term for the Saturated Adiabatic Lapse Rate. It is the rate of adiabatic temperature change in saturated air. The rate of temperature change is variable, but it is always less than the dry adiabatic rate.

White Frost: Ice crystals that form on surfaces instead of dew when the dew point is below freezing.

Wien's Displacement Law: The wavelength at which the blackbody emission spectrum is most intense varies inversely with the blackbody's temperature. The constant of proportionality is Wien's constant (about 2,900 Kelvin-µm).
λp = [2900/T (µm)]

Wind: Air flowing horizontally with respect to Earth's surface from high pressure areas to lower pressure areas. The windiest place on Earth is on the coast of Antarctica, where, at Cape Dennison, the yearly average wind speed is 44 miles per hour! To appreciate the power of wind, consider that on on March 10, 1869 high winds caused red snow to fall over central France! Apparently, high winds swept reddish dust from the Sahara desert all the way into France, where it became mixed with snow. They called it "blood snow". Another amazing fact: In February 1965, a "ghost train" moved across the prairies of North Dakota (on tracks), as strong prevailing winds pushed five empty cars about 90 miles from Portal to Minot! The strongest wind ever measured at the ground with a cup anemometer occurred on New Hampshire's Mt. Washington, when on April 12, 1934, a momentary gust reached 231mph!

Windchill: A measure of apparent temperature that uses the effects of wind and temperature on the cooling rate of the human body. The windchill chart translates the cooling power of the atmosphere with the wind to a temperature under nearly calm conditions. For a more detailed explanation and to see a chart of windchill, check out our FAQ page!

Wind Vane: An instrument used to determine wind direction. Differs from an aerovane in that it does not measure wind speed. It has no propeller.

Winter Solstice: See Solstice.

World Meteorological Organization (WMO): Established by the UN (United Nations), the WMO consists of more than 130 nations. The organization is responsible for gathering needed observational data and compiling some general prognostic charts.