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Ball lightning – a relatively rarely seen form of lightning, generally consisting of an orange or reddish ball of the order of a few cm to 30cm in diameter and of moderate luminosity, which may move up to 1 m/s horizontally with a lifetime of a second or two.
Barber pole – a thunderstorm updraft with a visual appearance including 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.
Barometer – an instrument for measuring atmospheric pressure.
Barometric pressure – the actual pressure value indicated by a pressure sensor.
Bitterly cold – in winter, bitterly cold or very cold, refers to more than seven degrees Celsius below normal.
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 – includes winter storm conditions of sustained winds or frequent gusts of 35 mph or more that cause major blowing and drifting of snow, reducing visibility to less than one-quarter mile for 3 or more hours. Extremely cold temperatures often are associated with dangerous blizzard conditions. In Canada, a blizzard described as a severe storm that lasts three or more hours, and brings low temperatures, strong winds and poor visibility due to blowing snow. In Australia, it is described as a violent and very cold wind which is loaded with snow, some of which has been raised from snow covered ground.
Blocking high – a high pressure area (anticyclone), often aloft, that remains nearly stationary or moves slowly compared to west-to-east motion. It blocks the movement eastward movement of low pressure areas (cyclones) at its latitude.
Blowing Dust – dust that is raised by the wind to moderate heights above the ground to a degree that horizontal visibility decreases to less than seven miles. Visibilities of 1/8 mile or less over a widespread area are criteria for a Blowing Dust Advisory.
Blowing sand – sand particles picked up from the surface of the earth by the wind to moderate heights above the ground, reducing the reported horizontal visibility to less than seven statute miles.
Blowing snow – wind driven snow that reduces visibility to six miles or less causing significant drifting. Blowing snow may be snow that is falling and/or loose snow on the ground picked up by the wind. In Canada, it is described as snow that is lifted by the wind from the earth's surface to a height of two meters or more.
Blowing spray – water droplets torn by the wind from a body of water, generally from the crests of waves, and carried up into the air in such quantities that they reduce the reported horizontal visibility to less than seven statute miles.
Blustery – descriptive term for gusty winds that accompany cold weather.
Breezy – wind in the range of 15 miles per hour to 25 mile per hour with mild or warm temperatures.
Brisk – wind in the range of 15 to 25 miles per hour when the temperature is cold.
Broken clouds – clouds which cover between 5/8ths and 7/8ths of the sky.