Subj : Weather Terms (B) Part 3 To : All From : Daryl Stout Date : Mon Oct 03 2016 12:06 am BKN Broken BL Abbreviation for Boundary Layer; a layer of air adjacent to a bounding surface. Specifically, the term most often refers to the planetary boundary layer, which is the layer within which the effects of friction are significant. For the earth, this layer is considered to be roughly the lowest one or two kilometers of the atmosphere. It is within this layer that temperatures are most strongly affected by daytime insolation and nighttime radiational cooling, and winds are affected by friction with the earth's surface. The effects of friction die out gradually w ith height, so the "top" of this layer cannot be defined exactly. Black Ice 1. Slang reference to patchy ice on roadways or other transportation surfaces that cannot easily be seen. 2. In hydrologic terms, transparent ice formed in rivers and lakes. Blackbody A hypothetical "body" that absorbs all of the electromagnetic radiation striking it - it does not reflect or transmit any of the incident radiation. A blackbody not only absorbs all wavelengths, but emits at all wavelengths with the maximum possible intensity for any given temperature. Blackbody Radiation The electromagnetic radiation emitted by an ideal blackbody adhering to the radiation laws; it is the theoretical maximum amount of electromagnetic radiation of all wavelengths that can be emitted by a body at a given temperature. BLD Build BLDUP Buildup Blizzard (abbrev. BLZD)- A blizzard means that the following conditions are expected to prevail for a period of 3 hours or longer: Sustained wind or frequent gusts to 35 miles an hour or greater; and Considerable falling and/or blowing snow (i.e., reducing visibility frequently to less than 1/4 mile) Blizzard Warning Issued for winter storms with sustained or frequent winds of 35 mph or higher with considerable falling and/or blowing snow that frequently reduces visibility to 1/4 of a mile or less. These conditions are expected to prevail for a minimum of 3 hours. BLO Below Blocked Flow Flow approaching a mountain barrier that is too weak or too stable to be carried over the barrier. Blowing A descriptor used to amplify observed weather phenomena whenever the phenomena are raised to a height of 6 feet or more above the ground Blowing Dust or Sand Strong winds over dry ground, that has little or no vegetation, can lift particles of dust or sand into the air. These airborne particles can reduce visibility, cause respiratory problems, and have an abrasive affect on machinery. A concentration reducing the visibility to ? mile or less often poses hazards for travelers. Blowing Snow Blowing snow is wind-driven snow that reduces surface visibility. Blowing snow can be falling snow or snow that has already accumulated but is picked up and blown by strong winds. Blowing snow is usually accompanied by drifting snow. Blowing Snow Advisory Issued when wind driven snow reduces surface visibility, possibly, hampering traveling. Blowing snow may be falling snow, or snow that has already accumulated but is picked up and blown by strong winds. Blue Watch or Blue Box [Slang], a severe thunderstorm watch. Blustery Same as Breezy; 15 to 25 mph winds. BLV before BLZD Blizzard- A blizzard means that the following conditions are expected to prevail for a period of 3 hours or longer: Sustained wind or frequent gusts to 35 miles an hour or greater; and Considerable falling and/or blowing snow (i.e., reducing visibility frequently to less than ? mile) BN Blowing Sand BNDRY Boundary Bomb Popular expression of a rapid intensification of a cyclone (low pressure) with surface pressure expected to fall by at least 24 millibars in 24 hour. Bora A regional downslope wind whose source is so cold that it is experienced as a cold wind, despite compression warming as it descends the lee slope of a mountain range. Border Ice In hydrologic terms, an ice sheet in the form of a long border attached to the bank or shore.; shore ice. Boundary Layer In general, a layer of air adjacent to a bounding surface. Specifically, the term most often refers to the planetary boundary layer, which is the layer within which the effects of friction are significant. For the earth, this layer is considered to be roughly the lowest one or two kilometers of the atmosphere. It is within this layer that temperatures are most strongly affected by daytime insolation and nighttime radiational cooling, and winds are affected by friction with the earth's surface. The effects of friction die out gradually with increasing height, so the "top" of this layer cannot be defined exactly. There is a thin layer immediately above the earth's surface known as the surface boundary layer (or simply the surface layer). This layer is only a portion of the planetary boundary layer, and represents the layer within which friction effects are more or less constant throughout (as opposed to decreasing with height, as they do above it). The surface boundary layer is roughly 10 meters thick (from the surface up to 10 m above the ground), but again the exact depth is indeterminate. Like friction, the effects of insolation and radiational cooling are strongest within this layer. Bounded Weak Echo Region (Also known as a vault.) Radar signature within a thunderstorm characterized by a local minimum in radar reflectivity at low levels which extends upward into, and is surrounded by, higher reflectivities aloft. This feature is associated with a strong updraft and is almost always found in the inflow region of a thunderstorm. It cannot be seen visually. BOVC Base of Overcast Bow Echo A radar echo which is linear but bent outward in a bow shape. Damaging straight-line winds often occur near the "crest" or center of a bow echo. Areas of circulation also can develop at either end of a bow echo, which sometimes can lead to tornado formation - especially in the left (usually northern) end, where the circulation exhibits cyclonic rotation. Bowen Ratio For any moist surface, the ratio of heat energy used for sensible heating (conduction and convection) to the heat energy used for latent heating (evaporation of water or sublimation of snow). The Bowen ratio ranges from about 0.1 for the ocean surface to more than 2.0 for deserts; negative values are also possible. It is named for Ira S. Bowen (1898-1978), an American astrophysicist. Box Model A computer model used to calculate air pollution concentrations. A box model is based on the assumption that pollutants are emitted into a box through which they are immediately and uniformly dispersed. The sides and bottom of the box are defined by the sidewalls and floor of the valley being studied. BR Mist Brackish Ice In hydrologic terms, ice formed from brackish water. Braided Stream In hydrologic terms, characterized by successive division and rejoining of streamflow with accompanying islands. A braided stream is composed of anabranches. Brash Ice In hydrologic terms, accumulation of floating ice made up of fragments not more than 2 meters across; the wreckage of other forms of ice. BRD Border Breach In hydrologic terms, the failed opening in a dam. Posted by VPost v1.7.081019 --- Virtual Advanced Ver 2 for DOS * Origin: The Thunderbolt BBS (801:1/7) þ Synchronet þ The Curmudeon's Place .