Weather Glossary – B


BACKING WINDS – A counterclockwise change in wind direction. Backing winds with height are indicative of cold air advection (CAA).

BAROCLINICITY– A cold air advection/warm air advection couplet that increases atmospheric instability. On analysis and forecast charts it is the isotherms crossing the height contours.

BAROTROPIC– Homogeneous atmosphere in which there are neither fronts nor any thermal advections.

BAROMETER An instrument for measuring atmospheric pressure.

BEAUFORT SCALE – a scale that indicates the wind speed using the effect wind has on certain familiar objects.

BLACKBODY– A mass which absorbs and emits all wavelengths of radiation

BLACK ICE – thin, new ice that forms on fresh water or dew covered surfaces; it is common on roadways during the fall and early winter and appears “black” because of its transparency.

BLIZZARD – A storm lasting about 3 hours or longer with sustained winds 35 mph or greater with frequent gusts to 35 mph or greater; and considerable falling and/or blowing snow frequently reducing visibilities to less than 1/4 mile.

BLOCKING PATTERN– A situation in which the upper tropospheric flow becomes highly meridional and stagnant. Two common blocking patterns are the omaga block and the rex block.

BLOWING DUST OR SAND – Small particles of dust or sand which are caused by strong winds blowing over dry ground, that has little or no vegetation.

BLOWING SNOW – Wind-driven snow which reduces surface visibility.

BOW ECHO – An accelerated portion of a squall line of thunderstorms, taking on a radar indicated bow configuration, created by strong downburst winds

BREEZY – Sustained winds of 15 to 25 mph.

BROKEN CLOUDS – Clouds which cover between 6/10 and 9/10 of the sky.