Weather Words - W

-- W --

Wadi: In areas of the Middle East and Northern Africa, a channel that carries water only during the rainy season. In the southwestern United States, the comparable term is arroyo.

Wall Cloud: The locally lowered portion of the base of a cumulonimbus cloud (thunderhead) into which intense updrafts are ascending. About 1-3 miles in diameter, it is the part of the thunderstorm base from which tornadoes develop.

Warm: (1) Having a moderate degree of heat, and of lesser intensity than hot. In the summer, the Chicago office of the National Weather Service uses warm or very warm for expected daily maximum temperatures in the middle or upper 80s. (2) Having a moderate degree of heat, but of lesser intensity than hot. In the spring, it generally refers to temperatures near 80 degrees, or a little above.

Warm front: (1) The transition zone between two air masses, one relatively cool and the other relatively warm, moving so that the warmer air replaces the cooler air; the "leading edge" of a warm air mass. (2) The boundary between an advancing mass of air that is warmer than the one it is replacing, usually at the point of contact with the ground.

Warm frontal passage: The movement across a location of the transition zone (front) between two air masses, one relatively warm and the other relatively cool, moving so that the warmer air replaces the cooler air.

Warm sector: That area within the circulation of a low pressure system in which the warmest air is found, usually the southeast quadrant. It is bounded by the system's cold front, usually extending southwestward from the center of low pressure, and its warm front, usually extending southeastward.

Warmer: When used in weather forecasts, it indicates that temperatures are expected to be higher than 24 hours earlier, and usually by an appreciable amount.

Warning: A forecast issued by the National Weather Service indicating that a specific hazardous weather or hydrologic event is imminent or actually occurring.

Wash: The dry bed of a stream, usually in an arid environment, and characterized by rare but large, high-energy discharges of water often containing large amounts of mud, rocks and debris.

"Washington and Jefferson Snowstorm": On January 27, 1772, George Washington reported three feet of snow at his residence, Mount Vernon, and Thomas Jefferson recorded about three feet of snow at Monticello.

Watch: (1) A forecast issued by the National Weather Service indicating that conditions are favorable (60 percent or greater likelihood) for the occurrence of a particular weather hazard. (2) A National Weather Service forecast indicating that conditions are favorable for the occurrence of a particular hazard. A watch is a recommendation for planning, preparation and increased awareness.

Water: (1) Water: The Earth is nearly drowned in water. If all the irregularities in the Earth's crust were ironed out, reducing the planet to a perfectly smooth sphere, the resulting ocean would completely submerge the globe to a uniform depth of about 8,000 feet. (2) The Earth is nearly drowned in water. Only 29 percent of the planet's surface is above sea level, and south of the Equator the sea engulfs 81 percent of the hemisphere. (3) 97 percent of the world's water is in the oceans and is salty; fresh water constitutes only 3 percent of all water, three quarters of which is locked up as ice, and most of the rest is in the ground. (4) Weighing 62.4 pounds per cubic foot, water is about 816 times more dense than air at sea level. (5) The most abundant material on the Earth's surface, but 97 percent of it is salty and only 3 percent is fresh. Of the 3 percent that is fresh: 2.2 percent is ice, 0.6 percent is in the ground and surface fresh water constitutes only 0.2 percent.

Water content: The depth of water that would result from the complete melting of solid precipitation (snow, sleet, hail) at a location; or, the depth of liquid water that would result from the complete melting of accumulated snow cover.

Water, density of: Water weighs 62.4 pounds per cubic foot and it is most dense (that is, a given volume is heaviest) when its temperature is 39.2 degrees F.

Water equivalent: The depth of water that results from the complete melting of a snow sample. Water equivalent varies greatly, but typically about 12 inches of snow will melt down to one inch of water, producing a water equivalent of 12 to 1.

Water pollution: (1) The presence in water of enough harmful or ojectionable material to damage the water's quality or usability. (2) The presence in water of substances that have or are likely to have deleterious effects, and usually applied only to substances in concentrations larger than occur naturally.

Water sky: The dark appearance of the underside of a cloud layer when it is over the open water on a large lake (like Lake Michigan).

Water vapor: Water substance in the gaseous (or vapor) phase. In the atmosphere, water vapor rarely occurs in concentrations greater than about four percent by volume.

Water vapor canopy: A massive "atmosphere" of water vapor surrounding the Earth which, upon condensation, supposedly gave rise to the oceans. The canopy theory, proposed in 1912, is scientifically groundless.

Waterlogged: Soil saturated with water, occurring when the water table stands at or near the surface, reaching into the root zone of plants. Waterlogged soil is detrimental to plants not accustomed to it.

Waterspout: (1) A rapidly rotating column of air, funnel-shaped or tubular, extending from the base of a cumulus or cumulonimbus cloud down to the surface of an ocean or lake and usually comparable in intensity to a dust devil over land. A tornado occurring over water is sometimes referred to as a waterspout. (2) A tornado over water. Also a rapidly rotating column of air extending from the base of a cloud down to the surface of an ocean or lake, usually comparable in intensity to a dust devil over land.

Wave cyclone: A low pressure system which forms on and moves along a front (boundary between two air masses); usually referred to merely as a wave. The wave cyclone is the most common form of mid-latitude low pressure system.

Wave length: In oceanography, the horizontal distance between the highest parts of two successive wave crests above the still water level, separated by a trough that is below the still water level.

Waves: Oceanographers identify three kinds of waves in water: SEA: waves first-formed in wind-blown water; SWELL: waves away from their formation area, traveling under their own momentum; SURF: waves breaking on shore.

Weak tornado: (1) Weak tornado: A tornado with a wind speed of 40-112 m.p.h.; F0 or F1 on the tornado F scale developed by Dr. T. Fujita of the University of Chicago. About 63 percent of all tornado occurrences are weak. (2) A tornado with a wind speed of 40-112 m.p.h.; F0 or F1 on the tornado F scale. About 63% of all tornado occurrences.

Weather: The short-term (minutes, hours, days) state of the atmosphere, mainly with respect to its effects upon living things. Weather is usually thought of in terms of temperature, humidity, precipitation, cloudiness, wind, visibility and brightness.

Weather Bureau established: 128 years ago (November 1, 1870), the first official United States weather service, the U.S. Weather Bureau, was created under President Ulysses S. Grant on November 1, 1870, as an agency within the War Department. In an administrative name change, the Weather Bureau later became the National Weather Service.

Weather elements: The variables by which the state of the weather is described: temperature, air pressure, wind, humidity, condensation forms (dew, frost, fog, clouds, precipitation), sunshine, visibility, ceiling (height of cloud bases).

Weather folklore: Tree leaves and rain: When tree leaves curl up or turn upside-down, it means rain. There is some truth to this: High humidity can cause leaves to curl, and shifting thunderstorm winds can flip leaves over.

Weather forecast: A statement of expected future occurrences of the weather up to 48 hours ahead, including such atmospheric variables as temperature, precipitation, amount of cloudiness, and wind direction and speed.

Weather myth: (1) Myth: Hurricanes contain raging thunderstorms. Fact: Few thunderstorms occur within hurricanes, and those that do form are usually located not in the core but in spiral rain bands at the storm's periphery. (2) Myth: A highway underpass is a good place to ride out a thunderstorm. Fact: The opposite is true. Underpasses offer protection from rain, but they funnel winds; high winds and debris blow more violently through underpasses. (3) Myth: Tornadoes strike mobile homes more often. Fact: Tornadoes do not strike mobile homes with greater frequency than other kinds of residential construction, but tornado deaths are higher in mobile homes because of their inability to withstand high winds and airborne debris. (4) Myth: Getting chilled can cause a cold. Fact: Cold viruses are not thought to be activated by exposure to cold. Studies indicate that chills resulting from exposure to cold temperatures and drafts have no effect on whether we catch a cold or on the severity of a cold. (5) Myth: There are a multitude of Eskimo words (50 or more) for snow. Fact: The various Eskimo languages (such as Inuit) and dialects contain only two distinct words meaning "snow": qanik (snowflakes in the air) and aput (snow on the ground). (6) Myth: It can be too cold to snow. Fact: It can never be too cold to snow. Snow -- light snow, but snow nonetheless -- has been observed many times at the South Pole Station in Antarctica with air temperatures below -50 degrees F, and occasionally below -70 degrees. (7) Myth: The Earth is farther from the sun in winter, closer in summer. Fact: Just the opposite is true. At closest approach in early January, the Earth is 91.7 million miles from the sun; farthest in early July, at 94.8 million miles (3.1 million miles farther out than in January.)

Weather observer: A person who, in cooperation with others, makes a regular record of the weather based upon a uniform plan. Good observing requires skills in punctuality, accuracy and in reading and setting instruments.

Weathering: The mechanical, chemical or biological action of the atmosphere upon the form, color and constitution of exposed material (rock, soil, buildings, etc.). Contrast with EROSION, which involves the movement of material.

Wedge tornado: A large tornado with a funnel that is as wide (horizontally) at the ground as it is tall (vertically) from the ground to the cloud base. A colloquial term used by storm chasers.

Wedging: Cold air that pushes south to the east of the spine of the Appalachian Mountains across Virginia, the Carolinas and north Georgia. When the cool air is shallow, it does not spill over the mountains.

Weighing rain gauge: A rain gauge which measures rainfall amounts by weighing rain captured in a bucket, then recording the readings on a graph. An analysis of the graph yields precipitation intensity as well as rain totals.

Westerlies (prevailing westerlies): The dominant west-to-east motion of the atmosphere centered over the middle latitudes of both hemispheres and paralleling the equator at 35-55 degrees N and S latitude. Most of the U.S. lies within the northern hemisphere zone of westerlies.

Western Hemisphere's highest temperature: On July 10, 1913, the temperature soared to 134 degrees at Greenland Ranch in Death Valley, Calif., the hottest reading of record for the North and South American continents. Sandstorm conditions accompanied the heat.

Wet day: A calendar day (midnight-midnight, standard time) on which measurable precipitation (0.01" or more water content) falls. Averaged from 1871 through 2005, Chicago experiences 124 wet days per year.

Wet season: In climates in which the seasonal variation of precipitation is a major feature (like coastal California), the wet season is the annually recurring period of a few months during which precipitation is at a maximum for that region. Chicago does not have a well-defined wet season.

Wetland: Land that has the water table at, near, or slightly above the land surface, or that is saturated for a long enough time to promote biological activity that is adapted to a wet environment.

"When the Gulf opens up": Weather forecasters' jargon for a situation in which moist air originating over the Gulf of Mexico spreads far inland (across the Midwest, for example), thereby enhancing precipitation produced by migrating weather systems.

Whirlwind: An imprecise, general term for a small-scale rotating column of air that is in contact with the ground. More specific terms are dust devil, waterspout, gustnado and tornado.

White desert: The appellation applied to Antarctica, whose unique weather and geography have resulted in a permanent ice cap over which the air is intensely cold and dry, and very little precipitation falls.

White dew: Dew that has frozen as a result of a fall in temperature to below freezing after the original formation of dew; hence, frozen dew. Frost, which forms in a sub-freezing environment, is not frozen dew.

White plague: A colloquial reference by farmers to hail, because in the United States hail causes annual damage of several hundred million dollars to field crops.

Whiteout: An atmospheric optical phenomenon in which the observer is engulfed in a uniformly white glow. Neither shadows, horizon, nor clouds are discernible. A sense of depth and orientation is lost.

Willy-willy: In Australia, a strong tropical cyclone (low pressure system) producing winds of 33 knots (38 m.p.h.) or greater; it is comparable in strength to a tropical storm (39-73 m.p.h.) in the Atlantic basin.

Wind: (1) The horizontal motion of air relative to the surface of the earth. Because vertical air motions are small near the surface, meteorologists use the term, wind, to refer only to the horizontal part of air motion. (2) The horizontal motion of air relative to the surface of the earth. Although stronger winds do occur, the world's highest MEASURED wind speed is a gust to 231 mph on April 12, 1934, at Mt. Washington, New Hampshire (3) The horizontal motion of air relative to the surface of the earth. Considered to be severe if 58 m.p.h. or greater. Hurricane winds are 74 m.p.h or greater. Highest tornado winds: about 318 m.p.h. (4) The horizontal motion of air relative to the Earth's surface. By convention, wind direction is the direction from which the wind blows. Thus, a south wind blows from south to north. (6) The horizontal movement of air relative to the ground. Onshore wind: Wind blowing from water to land. Offshore wind: Wind blowing from land to water.

Wind advisory: An issuance of the National Weather Service for the expected occurrence of sustained winds 29-38 m.p.h. lasting more than one hour, or for the occurrence of wind gusts 44-57 m.p.h.

Wind aloft: The wind speeds and directions at various levels in the atmosphere above the domain of surface weather observations; hence winds at any level above a few hundred feet off the ground.

Wind chill: That part of the total cooling of the human body caused by air motion. Only air temperature and wind speed are used in the calculation of wind chill temperatures; humidity and evaporative cooling are not taken into consideration.

Wind chill temperature: The temperature of still air that would remove heat from an exposed human body as quickly as it is being removed by the existing combination of actual air temperature and wind speed. Humidity and evaporative cooling are not taken into consideration.

Wind direction: (1) By convention, the direction from which the wind blows. Thus, a south wind blows from south to north. (2) By convention, wind direction is always stated as the direction from which the wind blows. Thus, a north wind blows from the north to the south.

Wind erosion: The movement of soil or rock from one point to another by the action of wind. It is a very important factor in the continued redistribution of Earth surface material.

Wind power: Electricity generated by windmills or mechanical power derived from a windmill (such as a grist mill or a windmill used to pump water).

Wind shear: The change of wind speed (speed shear) or wind direction (directional shear) over short distances, either vertically or horizontally.

Wind shift: The abrupt or gradual change in wind direction of 45 degrees or more that takes place in less than 15 minutes.

Wind sock: A cone-shaped, tapered fabric sleeve mounted at its larger end on a vertical pivot, for the purpose of indicating wind direction. (The small end of the cone points away from the wind.)

Wind turbine: An electricity-generating turbine powered by wind. Optimum operation requires that the rotating blades be kept clean -- a buildup of smashed insects can reduce efficiency by 50 percent.

Wind vane: A plate that swivels in the wind to show wind direction; also, a weather instrument that measures wind direction. Anemometers measure the speed of the wind.

Wind wave: A wave resulting from the action of wind on a water surface. While the wind is acting on it, it is called a SEA; thereafter, swell.

Windbreak: Any device designed to obstruct wind flow and intended for protection downwind against any ill effects of wind. Examples: snow fences, protective hedgerows.

Windburn: Superficial inflammation of the skin, analogous to sunburn, caused by exposure to wind, especially hot dry wind, inducing dilation of the surface blood vessels; also, injury to plant foliage caused by hot dry winds.

Windchill temperature: The apparent temperature of calm air that will remove heat from exposed human flesh as quickly as existing combination of air temperature and wind speed.

Windmill: A device that runs on energy generated by a wheel of adjustable blades rotated by the wind; widely used for pumping water, and now coming into increasing use for generation of electricity.

Windward: (1) The direction or side of any object or land mass (such as an island, mountain or region) that faces into the prevailing wind. (2) Into the wind; toward the point from which the wind is blowing; upwind. (3) The direction facing into the wind; upwind.

Windy: Used by the Chicago National Weather Service in weather forecast terminology to describe expected winds with sustained speeds of 15-30 m.p.h. At greater speeds, the term "very windy" is used.

Windy City: (1) Chicago's nickname, probably derived from the city's status as a frequent host city for political conventions in the 19th Century and from the reputation of its aggressive resident hucksters - and not intended as a commentary on its breezy climate. (2) Chicago's nickname, erroneously attributed to Charles Dana, editor of the New York Sun, who, according to legend, grew weary of Chicagoans boasting of the great success of the city's 1893 World's Columbian Exposition, and editorially called Chicago "that Windy City." Research offers no evidence to support that legend

Winter: The coldest season of the year. Astronomical winter extends from the winter solstice (Dec. 21) to the vernal equinox (March 21). Meteorological winter consists of Dec., Jan. and Feb.

Winter lag of seasons: The time between the shortest day (which is the time of minimum heat input from the sun--about Dec. 21) and the actual date of the average lowest temperatures (in Chicago, about January 16). Chicago's lag of seasons during the winter: about four weeks.

Winter preparedness week: During Winter Preparedness Week in Illinois, a group of agencies, including the National Weather Service, Triple A Chicago Motor Club, Red Cross and the Illinois and Indiana State Police cooperate to provide winter weather information, including Project Icepack, an effort to disseminate pertinent real-time road and weather information over the Internet. Simply enter "www.icepack.org" for information.

Winter tornadoes: Tornadoes can, and do, occur in all months of the year in the United States. In the winter months, their greatest frequency is in the Gulf states.

Winterkill: To die as a result of exposure to winter conditions, and especially the cold of winter; death of plants resulting from exposure to winter weather; also the plants or portions of them that were killed.

Wisconsin's highest temperature: 114 degrees at Wisconsin Dells on July 13, 1936. Wisconsin Dells is located in south-central Wisconsin about 170 miles northwest of Chicago.

Wisconsin's lowest temperature: -55 degrees F at Couderay on Feb. 4, 1996. Couderay is located in northwestern Wisconsin, about 380 miles northwest of Chicago.

Wisconsin's temperature extremes: Wisconsin's lowest and highest temperatures span a range of 169 degrees from -55 degrees F at Couderay on Feb. 4, 1996, to 114 degrees at Wisconsin Dells on July 13, 1936. On those same dates, Chicago recorded -14 degrees (O'Hare) and 102 degrees (Midway), respectively.

World evaporation: The equivalent of 104,000 cubic miles of liquid water evaporates into the atmosphere every year, and then returns as precipitation.

World Meteorological Organization (WMO): The specialized agency of the United Nations which coordinates, standardizes and improves meteorological activities throughout the world, and encourages the efficient exchange of weather information between countries.

World ocean: The whole body of salt water covering about 70 percent of the Earth's surface; average depth about 12,600 feet; greatest depth 35,839 feet (Marianas Trench, in the western Pacific Ocean).

World precipitation: Annual precipitation averaged across the world is estimated to be 33.82 inches, surprisingly close to Chicago's annual average of 35.82 inches.

World air pressure extremes: Highest 32.06 inches (Dec. 19, 2001 at Tosontsengel, Mongolia); lowest 25.69 inches (Oct. 12, 1979, 520 miles northwest of Guam in the eye of Typhoon Tip.)

World's annual precipitation: 33.82 inches; 23 percent falls on land, 77 percent over the world's seas. Chicago's annual precipitation, 35.82 inches, is slightly greater.

World's average temperature: 61 degrees, and it varies little from day to day or through the seasons. Chicago's average annual temperature (O'Hare International Airport data) is 12 degrees cooler, at 49 degrees.

World's coldest and hottest places: Plateau Station, Antarctica, is coldest with an average annual temperature of -70 degrees F; Dallol Depression, Ethiopia, is hottest with an average annual temperature of 94 degrees.

World's coldest temperature: -129 degrees (-128.6) at Vostok, Antarctica, on July 21, 1983. The elevation there is 11,220 feet above sea level.

World's extreme temperature range: 265 degrees, from 136 degrees at El Azizia, Libya (September 13, 1922) to -129 degrees at Vostok, Antarctica (July 21, 1983).

World's greatest 24-hour rainfall: 73.6 inches of rain poured down on Cilaos, Reunion (an island in the Indian Ocean) during a 24-hour period on March 15-16, 1952.

World's greatest 24-hour rainfall: 73.62 inches on March 15-16, 1952, at Cilaos on the island of Reunion (located in the western Indian Ocean 420 miles east of Madagascar).

World's greatest one-month precipitation total: 366.14 inches in July, 1861, at Cherrapunji, India. Chicago's greatest one-month precipitation total: 17.10 inches in August, 1987 (at O'Hare International Airport).

World's greatest one-year precipitation total: 1,042 (1041.78) inches at Cherrapunji, India, in 1861. Chicago's greatest one-year precipitation total based on official records from 1871 to the present: 49 inches in 1983.

World's greatest single snowstorm: A seven-day storm, Feb. 13-19, 1959, at the Mt. Shasta Ski Bowl in California delivered 189 inches of snow -- nearly 16 feet -- a world single-snowstorm record.

World's highest air pressure: 32.06 inches of mercury at Tosontsengel, Mongolia, at 2 a.m. on Dec. 19, 2001. The temperature at the time was -41 degrees F and two inches of snow covered the ground.

World's highest dew point: The record high dew point in the world is 93 degrees, observed near Dubai, on the Persian Gulf in the United Arab Emirates.

World's highest measured wind speed: The world's highest measured wind speed is a gust to 231 m.p.h. recorded on April 12, 1934, at Mt. Washington, New Hampshire.

World's highest temperature: 136 degrees F. at El Azizia, Libya, on September 13, 1922. The United States' highest temperature: 134 degrees F. at Death Valley, California, on July 10, 1913.

World's highest temperature: 136 degrees. at El Azizia, Libya, was recorded on Sept. 13, 1922. The United States' highest temperature: 134 degrees at Death Valley, Calif., on July 10, 1913.

World's largest two-minute temperature change: 49 degrees (from -4 to +45) at Spearfish, South Dakota, beginning at 5:30 a.m. Friday, Jan. 22, 1943, as warming chinook winds blew in.

World's lowest air pressure: 25.69 inches of mercury over the Pacific Ocean 520 miles northwest of Guam, in the eye of Typhoon Tip, on October 12, 1979.

World's lowest surface elevation: At 1,349 feet below sea level, the surface of the Dead Sea located on the border between Israel and Jordan is the world's lowest place.

World's lowest temperature: -129 degrees F (-128.6�) at Vostok, Antarctica, on July 21, 1983. The elevation of the Vostok Station is 11,220 feet above sea level.

World's sunniest place: The eastern Sahara Desert in northern Africa. On average, it receives 4,300 hours of sunshine per year, or 11 hours 46 minutes per day.

World's wettest/driest places: The world's wettest place: Mt. Waialeale, Hawaii, with average annual rainfall of 460 inches. The world's driest place: Arica, Chile, with average annual rainfall of 0.03 inches.

World's windiest place: Port Martin, Antarctica. It has an average wind speed of 40 m.p.h. (64 km/hour). It experiences gale force winds (sustained 39 m.p.h. or stronger) on more than 100 days per year.

Worldwide precipitation: Annual precipitation averaged across the world is estimated to be 33.82 inches, and this is the equivalent of an incredible 104,000 cubic miles of liquid water.

Worst Illinois (and U.S.) tornado: Though not a Chicago weather event, the Great Tri-State Tornado of March 18, 1925, deserves mention because it so profoundly affected Illinois. It was the largest, longest, fastest (62 m.p.h.), most destructive and most deadly U.S. tornado. It caused 695 deaths as it moved 219 miles from southeast Missouri across southern Illinois into southwest Indiana.

Wreck of the Edmund Fitzgerald: On this date (Nov. 10) in 1975, the 729-foot ore freighter Edmund Fitzgerald sank at 7:10 p.m. during a violent Lake Superior storm that brought 70 m.p.h. winds and 30-foot waves. All on board (29) were lost.

Wright Brothers: Wilbur and Orville. On Dec. 17, 1903, they initiated the age of aviation at Kitty Hawk, NC, with a 12-second, 120-foot, powered, controlled flight in a heavier-than-air machine.

WSR-88D: The acronym, derived from Weather Surveillance Radar-1988 Doppler, for the National Weather Service Doppler radar system currently deployed across the United States and commissioned in 1988.

Wx: Meteorological jargon and shorthand for the word, "weather"; as in fair wx, severe wx, wx forecast, etc.