Weather Words - B | Weather | WGNTV.com | WGN TV

Weather Words - B

-- B --

Back-building Thunderstorm: A thunderstorm in which new development takes place on the upwind side (usually the southwest side), causing the storm to remain stationary or propagate in a backward direction.

Back-door cold front: A cold front (the leading edge of an advancing cold air mass) that arrives in the Chicago area from the northeast. Cold fronts usually push across Chicago from the northwest or west.

Background radiation: Radiation that occurs naturally in the environment. Sources of background radiation include radioactive minerals in the earth and cosmic rays from outer space.

Backing: A gradual change in wind direction in a counterclockwise sense; for example, from west to southwest to south. Backing winds are the opposite of veering winds.

Backing winds: Winds that shift in a counterclockwise sense; for example, from west to southeast to south to southeast. Backing winds are the opposite of veering winds.

Backing/veering: Backing: A gradual change in wind direction in a counterclockwise sense; for example, from west to southwest to south. Veering: A gradual change in wind direction in a clockwise sense; for example, from south to southwest to west.

Backwash: Flowing back into the lake in shallow water, the brisk bottom current that waders feel pulling at their legs. Backwash returns to the lake water that was washed onto the shore by waves.

Bad hair day: A very humid or very dry day. Human hair, sensitive to the amount of moisture in the air regardless of temperature, expands when air is moist and contracts when it is dry -- it becomes unruly.

Bagdad, Calif.: The site (now abandoned) in the Mojave Desert in southern California, of the longest rain-free period in the United States: 767 days, from Oct. 3, 1912, through Nov. 8, 1914.

Baguio: A severe tropical cyclone (hurricane) in the Philippine Islands. The name derives from the Philippine city of Baguio, which holds the world record for 24-hour rainfall (46 inches) during the passage of a tropical cyclone in July 1911.

Bai: A mist that occurs in China and Japan in spring and fall, when loose earth is churned up by the wind so that clouds of dust rise to great heights, afterwards collecting moisture and falling as colored mist which produces a thick coating of very fine yellow dust.

Ball lightning: A rare form of lightning consisting of a luminous ball about one foot in diameter, often reddish in color, which may move rapidly along solid objects or remain floating in mid-air.

Balloon: A flexible bag inflated with a gas (such as helium) whose density at any given temperature and pressure is less than the density of surrounding air, thereby causing the bag to rise.

Bangladesh cyclone: On Nov. 12-13, 1970, a cyclone (as hurricanes of the Indian Ocean are known) with 150 m.p.h. winds and accompanying storm surge left an estimated 300,000 to 500,000 dead in Bangladesh.

Bangladesh hurricanes: Hurricanes have built frightful records of death and destruction. In Bangladesh in 1970, a typhoon (hurricane) with flooding rain, 120-150 m.p.h. winds and a massive storm surge claimed 300,000 lives.

Banner cloud: A stationary cloud plume often observed to extend a mile or more downwind from isolated mountain peaks, even on otherwise cloud-free days. Examples of banner clouds: Tursui over Mount Fuji and the Rock of Gibraltar banner.

Bar: A unit of air pressure equal to the pressure exerted at the bottom of a column of mercury 29.5306 inches in height; an air pressure value of 29.53 inches; 1,000 millibars.

Barber: A severe storm at sea during which precipitation and wind-driven spray freeze onto the decks and rigging of boats. In the Gulf of St. Lawrence, a barber is an especially severe blizzard in which wind-borne ice particles cut into the skin.

Barchan: A crescent-shaped dune or drift of windblown sand or snow. Conditions under which barchans form are a moderate supply of material (sand or snow) and winds of almost constant direction and of moderate strength; also spelled barchane and barkhan.

Barodontalgia: Pain in teeth associated with changes in barometric pressure. It usually affects flyers (flyer's toothache) and divers (diver's toothache), but in rare cases it is due to air pressure changes associated with the weather.

Barograph: A recording barometer; that is, a weather instrument which measures air pressure and makes a continuous line graph of the values.

Barometer: An instrument that measures air pressure. There are two general kinds: mercurial (highly accurate; never in need of recalibration) and aneroid (less accurate; requires occasional recalibration).

Barometric pressure: Air pressure; the pressure exerted by the atmosphere at a given point; the force exerted per unit area by the weight of the atmosphere. At sea level, air pressure is 14.7 pounds per square inch.

Barotrauma: A condition of discomfort in the ear caused by pressure differences between the inside and outside of the ear. It occurs when large air-pressure changes take place very quickly.

Barrow, Alaska: The coldest U.S. city, with an average annual temperature of 9.4 degrees F. Chicago's average annual temperature (O'Hare), 49.0 degrees, is about 40 degrees warmer.

Base flood: A flood having a one percent probability of being equaled or exceeded in a given year at a specific location; also known as a hundred-year flood.

Bayamo: A severe tropical thundersquall that occurs on the south coast of Cuba, especially near the Bight of Bayamo.

Bead lightning: Resembling pearls on a string, it is merely a particular aspect of normal lightning seen when the observer happens to view end-on a number of segments of the irregular lightning channel and hence receives an impression of higher intensity at a series of locations along the channel.

Beaufort, Admiral Sir Francis: (1774-1857) The British admiral and cartographer who devised the Beaufort wind scale, a 13-point scale of wind speeds ranging from 0 (calm) to 12 (hurricane) based upon the standard procedures for setting sails on a square-rigged ship.

Beaufort Wind Scale: A 13-point scale of wind speeds ranging from 0 (calm) to 12 (hurricane), originally devised by British Admiral Sir Francis Beaufort in 1806. It consisted of 13 descriptions of the state of the sea correlated with ranges of wind speeds.

Bentley, Wilson A.: The pioneer of photomicrography of snow crystals; starting in 1885 from his workplace in Jericho, Vermont, he produced more than 5000 exquisite pictures of snow crystals and snowflakes.

Bergy bit: An iceberg fragment or a small iceberg. It is larger than a growler.

Bermuda high: The semi-permanent subtropical high pressure system over the North Atlantic Ocean, so named because it is sometimes centered near Bermuda. It contributes to U.S. heat waves when it extends west into the Gulf of Mexico and across the Deep South.

Bernoulli's Principle: Named after Swiss mathematician and scientist Daniel Bernoulli (1700-1782) who discovered that as the speed of a fluid (like water or air) increases, its pressure decreases.

Big bags: A British colloquialism for cumulonimbus mamma, hanging protuberances, like pouches, on the under surface of the anvil of cumulonimbus clouds (the clouds that bring thunderstorms).

Big Thompson flash flood: On July 31, 1976, a stationary thunderstorm dumped 10 inches of rain into the canyon of the Big Thompson River in northeast Colorado. The resulting flash flood swept 25 miles from Estes Park to Loveland, killing 156 campers and tourists along the river.

Biofog: A type of fog formed by contact of extremely cold air with the shallow layer of warm moist air surrounding the bodies of humans or animals.

Biosphere: The zone at or near the Earth's surface in which all living things are found; the sphere of life.

Bird burst: Radar echoes caused by flocks of roosting birds that take to the air as a group and fly away in different directions. Bird bursts often occur at sunrise.

Bishop's ring: A dull reddish-brown ring observed around the sun following major volcanic eruptions, and first described by the Rev. S Bishop of Honolulu following the 1883 eruption of Krakatoa.

Bjerknes, Vilhelm: Norwegian physicist who laid the cornerstone for modern meteorological theory with his discovery in 1918 that weather patterns in the temperate middle latitudes resulted from the interaction of warm and cold air masses.

Black blizzard: A colloquial term for a dust storm over the south-central United States. Prerequisite to a black blizzard is a period of drought over an area of normally productive land.

Black Dragon Fire: Perhaps the largest forest fire in recorded history. It burned 28,000 square miles (half the area of Illinois) during April-May-June, 1987, from the Lake Baikal area of Siberia into north China.

lack ice: A thin layer of new ice on a lake or pond, appearing dark in color because of its transparency. In the 1980s the usage of the term broadened to include nearly invisible ice on concrete roadways.

Black rain: Following a nuclear detonation, it is rain colored black by debris from the blast. Radioactive black rain was first observed at Hiroshima, Japan, following the atomic blast there on August 6, 1945.

Black, Joseph: (1728-1799) Scottish chemist who, in 1756, while a student at the Univ. of Edinburgh, discovered the existence of carbon dioxide and proved it is a permanent, though small, constituent of air.

Blink: A brightening of the base of a cloud layer, caused by reflection of light from a snow-covered or ice-covered surface.

Blirty: In Scotland, gusts of wind and rain; changeable, uncertain, inclement weather.

Blizzard: An intense winter storm with sustained winds 35 m.p.h. or higher and sufficient falling and/or blowing snow to reduce visibility below 1/4 mile for at least three hours. U.S. blizzards occur mainly in the Great Plains and upper Midwest. Although the origin of the word blizzard is obscure, the word appeared in the United States and its first use was possibly on March 14, 1870, to describe a storm that produced heavy snow and high winds in Minnesota and Iowa. Severe blizzard: temperature at or below 10 degrees, winds exceeding 45 m.p.h. and zero visibility.

Blizzard Warning: Issued for winter storms with sustained or frequent winds of 35 m.p.h. or higher with falling and/or blowing snow that frequently reduces visibility to 1/4 mile or less. These conditions are expected to prevail for a minimum of 3 hours.

Blocking: The obstructing, on a large (1,000+ miles) scale, of the normal west-to-east progress of low pressure systems and high pressure systems.

Blocking high: A high pressure system that remains nearly stationary compared to the west-to-east motion of weather systems upstream from the high, so that it effectively prevents (blocks) the movement of migratory low pressure systems across its latitudes.

Blout: The sudden onset of a storm, or a sudden downpour of rain with hail and wind.

Blowdown: The massive felling of forests from the impact of thunderstorm winds, hurricanes, volcanic explosions and other natural phenomena.

Blowing dust: Dust picked up locally from the surface of the earth and blown about in clouds or sheets. In its extreme form, it is known as a dust storm.

Blowing sand: Sand that has been raised by the wind to a height of six feet or greater above the surface; reported in weather observations when it reduces visibility below seven miles.

Blowing snow: Fallen snow that has been raised by the wind to a height of six feet or greater above the surface; reported in weather observations when it reduces visibility below seven miles.

Blowing spray: Water droplets raised by the wind from the surface of a body of water to a height of six feet or greater above the water; reported in observations when it reduces visibility below seven miles.

Blue jet: Faintly visible discharges, blue in color, extending from the tops of thunderheads (cumulonimbus clouds) upward about 30 miles. The mechanism for generating blue jets is not understood.

Blue moon: The occurrence of two full moons in the same month, but never in February. A blue moon happens about every 32 months. A January blue moon is often followed by another in March, and that was the case in 1999. Two blue moons in one year will not occur again until 2018.

Blue norther: A blast of bitterly cold arctic air that surges south across Texas during the winter, bringing strong north winds and a sharp temperature drop.

Blue watch: A colloquial term used by meteorologists at the Storm Prediction Center (SPC) in Norman, Okla., denoting a severe thunderstorm watch. SPC issues the nation's severe weather watches.

Bluffart: In Scotland, a squall or strong wind accompanied by a sudden but brief fall of snow.

Blunk: In England, a fit of squally, tempestuous weather; a sudden squall.

Blustery: Windy, unsettled and stormy when applied to the weather. When used to describe wind alone, it refers to strong (generally above 20 m.p.h.) and very gusty winds.

Bolide: A meteor that explodes into fragments as it heats up due to friction with the earth's atmosphere. Once in a while the debris particles reach Earth's surface as meteorites.

Bombogenesis: A colloquial term for sudden, extremely rapid (almost explosive) intensification of low pressure systems just off the U.S. Atlantic Coast. These systems bring high winds, coastal flooding and very heavy precipitation.

Bora: The winds resulting from the motion of very cold air which, because its great density is strongly acted upon by gravity, flows off the highlands of the former Yugoslavia down to the Adriatic Sea. More generally, bora winds are cold winds that descend mountain slopes. Descending air warms as much as 5 degrees per 1,000 feet of vertical descent, but in bora situations the air is originally so cold that it is still cold even after warming during descent.

Boundary layer: The layer of air from the surface up to 3-5 thousand feet in which most of the daily temperature variation occurs as a result of heating and cooling of the ground by sunlight.

Boulder, Colorado, chinook winds: Chinooks are warm dry winds that blow down the eastern slopes of the Rocky Mountains, sometimes with extreme strength. On Jan. 17, 1982, Boulder suffered great damage when chinook winds gusted to 137 m.p.h. in the city.

Bow Echo: (1) A rapidly moving radar precipitation return that is bow shaped in the direction of motion of the thunderstorms producing the precipitation; a bow echo is associated with strong, straight-line winds.

Bow echo: (2) A rapidly-moving radar echo consisting of thunderstorms in an outward-bulging (bow) line. Damaging winds often occur near the crest of a bow echo. Bows are usually 25-125 miles in length.

Bowl of New Orleans: That portion of New Orleans, about 70 percent of the city (including the downtown section), that lies below sea level. It is the area most vulnerable to flooding from hurricane surge.

Brackish water: Water containing dissolved minerals in amounts that exceed acceptable standards for municipal, domestic and irrigation uses -- about 1000-4000 parts per million total dissolved solids.

Brazil: The lightning capital of the world. It experiences more lightning ground strikes per year, 70 million, than any other nation. In the United States, the comparable annual figure is 22 million.

Breaker (breaking wave): The foaming white turbulent mass of water that forms when a sea-surface wave has become too steep to be stable. When the wave's steepness (ratio of wave height to distance between wave crests) exceeds 1/7, the wave crest outraces the body of the wave and it breaks.

Breakup: The time when a river whose surface, frozen bank-to-bank for a significant part of the river's length, begins to change to open water flow. Breakup is often associated with ice jams and flooding.

Breakup date: In hydrologic terms, the date on which a body of water is first observed to be entirely clear of ice and remains clear thereafter. The breakup date for Lake Michigan is usually in late April or early May.

Breeze: In colloquial usage, a light wind. In the Beaufort wind scale, any wind ranging from 4 to 31 m.p.h. and categorized as: light breeze (4-7 m.p.h.), gentle breeze (8-12 m.p.h.), moderate breeze (13-18 m.p.h.), fresh breeze (19-24 m.p.h.), strong breeze 25-31 m.p.h.).

Brickfielder: In the days when Australia was a British colony, strong southerly winds that carried red dust across Sydney, Australia, from brickworks then located south of the city were called brickfielders.

Brisk: Sharp, stimulating and invigorating weather. In the Midwest, the term is applicable in autumn and spring because in the winter it is too cold to be considered brisk, and in the summer it is too warm.

British Isles' highest temperature: 99 degrees F on August 3, 1990, at Cheltenham, England. The British Isles are comprised of England, Ireland, Northern Ireland, Scotland and Wales.

British Isles' lowest temperature: -17 degrees F on January 10, 1982, at Braemar, Scotland. Braemar is located in the Grampian Mountains in north-central Scotland.

British thermal unit (BTU): A unit of heat energy equal to the amount of heat required to raise one pound of water from 60 to 61 degrees Fahrenheit at a constant pressure of one atmosphere.

Broken cloudiness: Descriptive of an amount of cloudiness covering 60 to 90 percent of the sky, at least half of which is opaque. If less than half the cloud layer is opaque, the layer is called thin broken.

Brontide: The low rumbling of distant thunder.

Brontology: The scientific study of thunder.

Brontophobia: The irrational or morbid fear of thunder.

Brown snow: Snow intermixed with dust and therefore colored brown. Snow of other colors (red, yellow) is similarly explained. Snow colored by dust occurs mainly in areas which experience light precipitation.

Bubble high: A small high pressure system, of the order of 50-300 miles across, often produced by precipitation or vertical currents associated with thunderstorms. They are transitory features and consist of relatively cool air.

Bucket thermometer: A thermometer used to measure sea temperatures. It is lowered into the sea on a line and remains in the water until it has had time to reach the temperature of the water, then it is withdrawn and read.

Build up, the: In tropical northern Australia, the transition, usually during the month of November, from the winter dry season to the summer wet season. It is a period of very high temperatures and humidity.

Bumpiness: The jolting sensation experienced in an aircraft that is flying through air that contains localized ascending and descending currents.

Burraxka silch: The local name for a hailstorm occurring in the Mediterranean Sea, near Malta.

Bust: A slang term used by meteorologists to denote an inaccurate weather forecast -- usually a situation in which a significant weather event was expected, but did not occur.

Buttermilk sky: A sky peppered with patches of mid-level altocumulus clouds or high-level cirrocumulus clouds that take on a globular appearance similar to the texture of cultured milk; a mackerel sky.

Buys-Ballot, Christoph: (1817-1890) The Dutch meteorologist who, in 1857, first described the relation between air pressure and wind direction, namely that with your back to the wind lower air pressure is to your left and higher air pressure is to your right.

Buys Ballot's law: If, in the Northern Hemisphere, you stand with your back to the wind, high pressure is on your right and low pressure is on your left; in the Southern Hemisphere, high pressure is on your left and low pressure is on your right.