24/7 Weather Glossary -- B Words
A | B | C | D | E | F | G | H | I | J and K | L | M | N | O | P | Q and R | S | T | U | V | W | X, Y and Z BACK BUILDING THUNDERSTORM
A thunderstorm in which new development takes place on the upwind side (usually the west or southwest side), such that the storm seems to remain stationary or propagate in a backward direction.BACKING
A counterclockwise shift in the wind direction in the Northern Hemisphere at a certain location. In the Southern Hemisphere, it is clockwise. This can either happen in the horizontal or the vertical (with height). For example, the wind shifts from the northeast to the north to the northwest. It is the opposite of veering.
BACKSCATTER
A radar echo that is reflected, or scattered, at 180 degrees to the direction of the incident wave. Also the scattering of radiant energy into space before it reaches the earth's surface.BACK DOOR COLD FRONT
A cold front that moves south-southwest out of Canada into the Northeastern United States along the Atlantic Seaboard.BACK SHEARED ANVIL
[Slang], a thunderstorm anvil that spreads upwind, against the flow aloft. A back-sheared anvil often implies a very strong updraft and a high severe weather potential.BALL LIGHTNING
A relatively rare form of lightning consisting of a luminous ball, often reddish in color, which moves rapidly along solid objects or remains floating in mid-air.BARBER POLE
[Slang], a thunderstorm updraft with a visual appearance that includes cloud striations that are curved in a manner similar to the stripes of a barber pole. The structure typically is most pronounced on the leading edge of the updraft, while drier air from the rear flank downdraft often erodes the clouds on the trailing side of the updraft.BAROCLINITY
The state of stratification in a fluid in which surfaces of constant pressure intersect surfaces of constant density. Also known as baroclinicity. An example is the tight temperature gradient along the East Coast of the United States during the winter that gives rise to intense cyclogenesis.BAROGRAPH
An instrument that continuously records a barometer's reading of atmospheric pressure.BAROMETER
An instrument used to measure atmospheric pressure. Two examples are the aneroid barometer and the mercurial barometer.BAROMETRIC PRESSURE
The pressure exerted by the atmosphere at a given point. Its measurement can be expressed in several ways. One is in millibars. Another is in inches or millimeters of mercury (Hg).BAROTROPY
The state of a fluid in which surfaces of constant density or temperature are coincident with surfaces of constant pressure. It is considered zero baroclinity.BARRIER WINDS
Refers to the westerly flow of air along the northern slope of the Brooks Range in northern Alaska that precedes the arrival of colder air from the north.BATHYTHERMOGRAPH
A device used to obtain a record of temperature against depth (pressure) in the ocean. May be referred to as a B.T.BEAR'S CAGE
A region of storm-scale rotation, in a thunderstorm, which is wrapped in heavy precipitation. This area often coincides with a radar hook echo and/or mesocyclone, especially one associated with an HP storm. The term reflects the danger involved in observing such an area visually, which must be done at close range in low visibility.BEAUFORT WIND SCALE
A system of estimating and reporting wind speeds. It is based on the Beaufort Force or Number, which is composed of the wind speed, a descriptive term, and the visible effects upon land objects and/or sea surfaces. The scale was devised by Sir Francis Beaufort (1777-1857), hydrographer to the British Royal Navy.BEAVER'S TAIL
A particular type of inflow band with a relatively broad, flat appearance suggestive of a beaver's tail. It is attached to a supercell's general updraft and is oriented roughly parallel to the pseudo-warm front, i.e., usually east to west or southeast to northwest. As with any inflow band, cloud elements move toward the updraft, i.e., toward the west or northwest. Its size and shape change as the strength of the inflow changes. See also inflow stinger.Spotters should note the distinction between a beaver tail and a tail cloud. A "true" tail cloud typically is attached to the wall cloud and has a cloud base at about the same level as the wall cloud itself. A beaver tail, on the other hand, is not attached to the wall cloud and has a cloud base at about the same height as the updraft base (which by definition is higher than the wall cloud). Unlike the beaver tail, the tail cloud forms from air that is flowing from the storm's main precipitation cascade region (or outflow region). Thus, it can be oriented at a large angle to the pseudo-warm front.BELLOT WINDS
Refers to the winds in the Canadian Arctic that blow through the narrow Bellot Strait between Somerset Island and the Boothia Peninsula, connecting the Gulf of Boothia and Franklin Strait.BERMUDA HIGH
A semi-permanent, subtropical area of high pressure in the North Atlantic Ocean that migrates east and west with varying central pressure. Depending on the season, it has different names. When it is displaced westward, during the Northern Hemispheric summer and fall, the center is located in the western North Atlantic, near Bermuda. In the winter and early spring, it is primarily centered near the Azores Islands.BERNOULLI'S THEOREM
A statement of the conservation of energy for a steady, nonviscous, incompressible level flow. It is an inverse relationship in which pressures are least where velocities are greatest. Theorized by Daniel Bernoulli (1700-1782), a Swiss mathematician and physicist.BIOSPHERE
The transition zone between the earth and the atmosphere within which most terrestrial life forms are found. It is considered the outer portion of the geosphere and the inner or lower portion of the atmosphere.BLACK BLIZZARD
A local term for a violent duststorm on the south-central Great Plains that darkens the sky and casts a pall over the land.BLACK ICE
Thin, new ice on fresh or salt water that appears dark in color because of its transparency. Also refers to thin, transparent ice on road surfaces.BLIZZARD
A severe weather condition characterized by low temperatures, winds 35 mph or greater, and sufficient falling and/or blowing snow in the air to frequently reduce visibility to 1/4 mile or less for a duration of at least 3 hours. A severe blizzard is characterized by temperatures near or below 10°F, winds exceeding 45 mph, and visibility reduced by snow to near zero.BLOCKING HIGH
The development of a warm ridge or cutoff high aloft at high latitudes which becomes associated with a cold high at the surface, causing a split in the westerly winds. Such a high will move very slowly, tending to move westward during intensification and eastward during dissipation. It prevents the movement of migratory cyclones across its latitudes.BLOWING DUST
Dust that is raised by the wind to heights of six feet or greater. It is reported as "BLDU" in an observation and on the METAR.BLOWING SAND
Sand that is raised by the wind to heights of six feet or greater. It is reported as "BLSA" in an observation and on the METAR.BLOWING SNOW
Snow that is raised by the wind to heights of six feet or greater. It is reported as "BLSN" in an observation and on the METAR.BLOWING SPRAY
Salt spray that is raised by the wind to heights of six feet or greater. It is reported as "BLPY" in an observation and on the METAR.BLUE NORTHER
Refers to a swift-moving cold frontal passage in the southern Great Plains, marked by a dark, blue-black sky with strong wintery winds from the northwest or north and temperatures that may drop 20°F to 30°F in a few minutes.BOILING POINT
The temperature at which a liquid changes to a vaporous state. The temperature at which the equilibrium vapor pressure between a liquid and its vapor is equal to the external pressure on the liquid. The boiling point of pure water at standard pressure is 100°C or 212°F.BORA WIND
It is a down-sloping wind along the Front Range, but it is different from the Chinook. Bora winds are very cold winds as they typically form just after a cold front has passed through the region. The pressure gradient is very tight after the front passes by and the winds can reach speeds of 50-60 mph. Despite the warming caused by the air sinking down from the mountains, the Bora is still a cold wind because the air was so chilly to begin with. In addition, Bora winds come in from the northwest instead of the west, so the mountains are not as tall over southern Wyoming and Larimer county.BOULDER WIND
A local name referring to an extremely strong downslope wind in the Front Range of the Rocky Mountains near Boulder, Colorado.BOUNDARY LAYER
The lowest layer of the earth's atmosphere, usually up to 3,300 feet, or one kilometer, from the earth's surface, where the wind is influenced by the friction of the earth's surface and the objects on it.BOW ECHO
A radar echo signature often associated with severe thunderstorms, especially those that produce wind damage. It is bent outward in a "bow" shape.BOYLE'S LAW
States that when the temperature is held constant, the volume of a gas is inversely proportional to its pressure. Therefore, if the pressure increases, the volume decreases and visa versa. For example, if the volume if halved, then the pressure is doubled. If the temperature is held constant, it becomes an isothermal process. Discovered by Robert Boyle (1627-1691), an Irish physicist and chemist and co-founder of the Royal Society.BRIGHT BAND
A narrow, intense radar echo due to water-covered ice particles at the melting level where reflectivity is at its greatest.BROKEN
The amount of sky cover for a cloud layer between 5/8ths and 7/8ths, based on the summation layer amount for that layer.BUBBLE HIGH
A small high that may be created by precipitation and vertical instability associated with thunderstorm activity. A product of downdrafts, it is relatively cold and often has the characteristics of a different air mass. Convergence along the leading edge of a bubble high may help form additional thunderstorms.BULK RICHARDSON NUMBER (or BRN)
A non-dimensional number relating vertical stability and vertical shear (generally, stability divided by shear). High values indicate unstable and/or weakly-sheared environments; low values indicate weak instability and/or strong vertical shear. Generally, values in the range of around 50 to 100 suggest environmental conditions favorable for supercell development.BUYS BALLOT'S LAW
Describes the relationship of the horizontal wind direction to the pressure distribution. In the Northern Hemisphere, if one stands with one's back to the wind, the pressure on one's left is lower than the pressure on one's right. It is reversed in the Southern Hemisphere. This law was named after the Dutch meteorologist, Buys Ballot, who developed the formula in 1857.BWER
Acronym for Bounded Weak Echo Region. Refers to radar echo signatures with low reflectivity in the center, surrounded by higher reflectivity. It is associated with strong updrafts and is found in the inflow region of a thunderstorm. A | B | C | D | E | F | G | H | I | J and K | L | M | N | O | P | Q and R | S | T | U | V | W | X, Y and Z
A thunderstorm in which new development takes place on the upwind side (usually the west or southwest side), such that the storm seems to remain stationary or propagate in a backward direction.BACKING
A counterclockwise shift in the wind direction in the Northern Hemisphere at a certain location. In the Southern Hemisphere, it is clockwise. This can either happen in the horizontal or the vertical (with height). For example, the wind shifts from the northeast to the north to the northwest. It is the opposite of veering.
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A radar echo that is reflected, or scattered, at 180 degrees to the direction of the incident wave. Also the scattering of radiant energy into space before it reaches the earth's surface.BACK DOOR COLD FRONT
A cold front that moves south-southwest out of Canada into the Northeastern United States along the Atlantic Seaboard.BACK SHEARED ANVIL
[Slang], a thunderstorm anvil that spreads upwind, against the flow aloft. A back-sheared anvil often implies a very strong updraft and a high severe weather potential.BALL LIGHTNING
A relatively rare form of lightning consisting of a luminous ball, often reddish in color, which moves rapidly along solid objects or remains floating in mid-air.BARBER POLE
[Slang], a thunderstorm updraft with a visual appearance that includes cloud striations that are curved in a manner similar to the stripes of a barber pole. The structure typically is most pronounced on the leading edge of the updraft, while drier air from the rear flank downdraft often erodes the clouds on the trailing side of the updraft.BAROCLINITY
The state of stratification in a fluid in which surfaces of constant pressure intersect surfaces of constant density. Also known as baroclinicity. An example is the tight temperature gradient along the East Coast of the United States during the winter that gives rise to intense cyclogenesis.BAROGRAPH
An instrument that continuously records a barometer's reading of atmospheric pressure.BAROMETER
An instrument used to measure atmospheric pressure. Two examples are the aneroid barometer and the mercurial barometer.BAROMETRIC PRESSURE
The pressure exerted by the atmosphere at a given point. Its measurement can be expressed in several ways. One is in millibars. Another is in inches or millimeters of mercury (Hg).BAROTROPY
The state of a fluid in which surfaces of constant density or temperature are coincident with surfaces of constant pressure. It is considered zero baroclinity.BARRIER WINDS
Refers to the westerly flow of air along the northern slope of the Brooks Range in northern Alaska that precedes the arrival of colder air from the north.BATHYTHERMOGRAPH
A device used to obtain a record of temperature against depth (pressure) in the ocean. May be referred to as a B.T.BEAR'S CAGE
A region of storm-scale rotation, in a thunderstorm, which is wrapped in heavy precipitation. This area often coincides with a radar hook echo and/or mesocyclone, especially one associated with an HP storm. The term reflects the danger involved in observing such an area visually, which must be done at close range in low visibility.BEAUFORT WIND SCALE
A system of estimating and reporting wind speeds. It is based on the Beaufort Force or Number, which is composed of the wind speed, a descriptive term, and the visible effects upon land objects and/or sea surfaces. The scale was devised by Sir Francis Beaufort (1777-1857), hydrographer to the British Royal Navy.BEAVER'S TAIL
A particular type of inflow band with a relatively broad, flat appearance suggestive of a beaver's tail. It is attached to a supercell's general updraft and is oriented roughly parallel to the pseudo-warm front, i.e., usually east to west or southeast to northwest. As with any inflow band, cloud elements move toward the updraft, i.e., toward the west or northwest. Its size and shape change as the strength of the inflow changes. See also inflow stinger.Spotters should note the distinction between a beaver tail and a tail cloud. A "true" tail cloud typically is attached to the wall cloud and has a cloud base at about the same level as the wall cloud itself. A beaver tail, on the other hand, is not attached to the wall cloud and has a cloud base at about the same height as the updraft base (which by definition is higher than the wall cloud). Unlike the beaver tail, the tail cloud forms from air that is flowing from the storm's main precipitation cascade region (or outflow region). Thus, it can be oriented at a large angle to the pseudo-warm front.BELLOT WINDS
Refers to the winds in the Canadian Arctic that blow through the narrow Bellot Strait between Somerset Island and the Boothia Peninsula, connecting the Gulf of Boothia and Franklin Strait.BERMUDA HIGH
A semi-permanent, subtropical area of high pressure in the North Atlantic Ocean that migrates east and west with varying central pressure. Depending on the season, it has different names. When it is displaced westward, during the Northern Hemispheric summer and fall, the center is located in the western North Atlantic, near Bermuda. In the winter and early spring, it is primarily centered near the Azores Islands.BERNOULLI'S THEOREM
A statement of the conservation of energy for a steady, nonviscous, incompressible level flow. It is an inverse relationship in which pressures are least where velocities are greatest. Theorized by Daniel Bernoulli (1700-1782), a Swiss mathematician and physicist.BIOSPHERE
The transition zone between the earth and the atmosphere within which most terrestrial life forms are found. It is considered the outer portion of the geosphere and the inner or lower portion of the atmosphere.BLACK BLIZZARD
A local term for a violent duststorm on the south-central Great Plains that darkens the sky and casts a pall over the land.BLACK ICE
Thin, new ice on fresh or salt water that appears dark in color because of its transparency. Also refers to thin, transparent ice on road surfaces.BLIZZARD
A severe weather condition characterized by low temperatures, winds 35 mph or greater, and sufficient falling and/or blowing snow in the air to frequently reduce visibility to 1/4 mile or less for a duration of at least 3 hours. A severe blizzard is characterized by temperatures near or below 10°F, winds exceeding 45 mph, and visibility reduced by snow to near zero.BLOCKING HIGH
The development of a warm ridge or cutoff high aloft at high latitudes which becomes associated with a cold high at the surface, causing a split in the westerly winds. Such a high will move very slowly, tending to move westward during intensification and eastward during dissipation. It prevents the movement of migratory cyclones across its latitudes.BLOWING DUST
Dust that is raised by the wind to heights of six feet or greater. It is reported as "BLDU" in an observation and on the METAR.BLOWING SAND
Sand that is raised by the wind to heights of six feet or greater. It is reported as "BLSA" in an observation and on the METAR.BLOWING SNOW
Snow that is raised by the wind to heights of six feet or greater. It is reported as "BLSN" in an observation and on the METAR.BLOWING SPRAY
Salt spray that is raised by the wind to heights of six feet or greater. It is reported as "BLPY" in an observation and on the METAR.BLUE NORTHER
Refers to a swift-moving cold frontal passage in the southern Great Plains, marked by a dark, blue-black sky with strong wintery winds from the northwest or north and temperatures that may drop 20°F to 30°F in a few minutes.BOILING POINT
The temperature at which a liquid changes to a vaporous state. The temperature at which the equilibrium vapor pressure between a liquid and its vapor is equal to the external pressure on the liquid. The boiling point of pure water at standard pressure is 100°C or 212°F.BORA WIND
It is a down-sloping wind along the Front Range, but it is different from the Chinook. Bora winds are very cold winds as they typically form just after a cold front has passed through the region. The pressure gradient is very tight after the front passes by and the winds can reach speeds of 50-60 mph. Despite the warming caused by the air sinking down from the mountains, the Bora is still a cold wind because the air was so chilly to begin with. In addition, Bora winds come in from the northwest instead of the west, so the mountains are not as tall over southern Wyoming and Larimer county.BOULDER WIND
A local name referring to an extremely strong downslope wind in the Front Range of the Rocky Mountains near Boulder, Colorado.BOUNDARY LAYER
The lowest layer of the earth's atmosphere, usually up to 3,300 feet, or one kilometer, from the earth's surface, where the wind is influenced by the friction of the earth's surface and the objects on it.BOW ECHO
A radar echo signature often associated with severe thunderstorms, especially those that produce wind damage. It is bent outward in a "bow" shape.BOYLE'S LAW
States that when the temperature is held constant, the volume of a gas is inversely proportional to its pressure. Therefore, if the pressure increases, the volume decreases and visa versa. For example, if the volume if halved, then the pressure is doubled. If the temperature is held constant, it becomes an isothermal process. Discovered by Robert Boyle (1627-1691), an Irish physicist and chemist and co-founder of the Royal Society.BRIGHT BAND
A narrow, intense radar echo due to water-covered ice particles at the melting level where reflectivity is at its greatest.BROKEN
The amount of sky cover for a cloud layer between 5/8ths and 7/8ths, based on the summation layer amount for that layer.BUBBLE HIGH
A small high that may be created by precipitation and vertical instability associated with thunderstorm activity. A product of downdrafts, it is relatively cold and often has the characteristics of a different air mass. Convergence along the leading edge of a bubble high may help form additional thunderstorms.BULK RICHARDSON NUMBER (or BRN)
A non-dimensional number relating vertical stability and vertical shear (generally, stability divided by shear). High values indicate unstable and/or weakly-sheared environments; low values indicate weak instability and/or strong vertical shear. Generally, values in the range of around 50 to 100 suggest environmental conditions favorable for supercell development.BUYS BALLOT'S LAW
Describes the relationship of the horizontal wind direction to the pressure distribution. In the Northern Hemisphere, if one stands with one's back to the wind, the pressure on one's left is lower than the pressure on one's right. It is reversed in the Southern Hemisphere. This law was named after the Dutch meteorologist, Buys Ballot, who developed the formula in 1857.BWER
Acronym for Bounded Weak Echo Region. Refers to radar echo signatures with low reflectivity in the center, surrounded by higher reflectivity. It is associated with strong updrafts and is found in the inflow region of a thunderstorm. A | B | C | D | E | F | G | H | I | J and K | L | M | N | O | P | Q and R | S | T | U | V | W | X, Y and Z
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