AVHRRAdvanced Very High Resolution Radiometer. Main sensor on U.S. polar orbiting satellites.
Aviation gasolineAll special grades of gasoline for use in aviation reciprocating engines, as given in the American Society for Testing and Materials (ASTM) specification…
AVNThe Aviation model (120-hour numerical model of the atmosphere). The output from this model is now part of what is known as the GFS model.
AVPOn a buoy report, Average Wave Period is the average period (seconds) of the highest one-third of the wave observed during a 20 minute sampling period.
AzimuthA direction in terms of a 360° compass. North is at 0°, east is at 90°, south is at 180°, and west is at 270°.
Azimuth AngleThe direction or bearing toward which a sloping surface faces (e.g., a north-facing slope has an azimuth angle of 360°; a northeast-facing slope, an…
Azores CurrentOne of the currents of the North Atlantic subtropical gyre.
Azores HighAlternate term for Bermuda High - a semi-permanent, subtropical area of high pressure in the North Atlantic Ocean off the East Coast of North America that…
BAbbreviation used on long-term climate outlooks issued by CPC to indicate areas that are likely to be below normal for a given parameter (temperature…
Back Door Cold FrontA cold front moving south or southwest along the Atlantic seaboard and Great Lakes; these are especially common during the spring months.
Back-building ThunderstormA thunderstorm in which new development takes place on the upwind side (usually the west or southwest side), such that the storm seems to remain…
Back-sheared Anvil[Slang], a thunderstorm anvil which spreads upwind, against the flow aloft. A back-sheared anvil often implies a very strong updraft and a high severe…
BackfireA fire started to stop an advancing fire by creating a burned area in its path.
BackflowA reverse flow condition, created by a difference in water pressures, which causes water to flow back into the distribution system.
BackingAny type of line used to partially fill a reel before the main fishing line is added; commonly used in fly-fishing or by bass anglers who use many of the…
Backing WindsWinds which shift in a counterclockwise direction with time at a given location (e.g.
BackscatterThe portion of power scattered back in the incident direction.
backscattered radiationThe scattering of radiant energy into the hemisphere of space bounded by a plane normal to the direction of the incident radiation and lying on the same…
BacksightA rod reading taken on a point of known elevation, a benchmark or a turning point.
Backwater CurveThe longitudinal profile of the surface of a liquid in a non-uniform flow in an open channel, when the water surface is not parallel to the invert owing…
Backwater EffectThe effect which a dam or other obstruction or construction has in raising the surface of the water upstream from it.
Backwater FloodingUpstream flooding caused by downstream conditions such as channel restriction and/ or high flow in a downstream confluence stream.
Bacteria(bak-TEER-ee-uh) A large group of single-cell microorganisms. Some cause infections and disease in animals and humans.
BANDPASS FILTERA filter whose frequencies are between given upper and lower cutoff values, while substantially attenuating all frequencies outside these values (this…
BandwidthThe amount of information or data that can be sent over a network connection in a given period of time.
BankAmerica has a "dual banking system" which means that both states and the federal government issue bank charters for the need and convenience of their…
Bank StorageWater that has inflitrated from a reservoir into the surrounding land where it remains in storage until water level in the reservoir is lowered.
BankfullThe water level, or stage, at which a stream, river or lake is at the top of its banks and any further rise would result in water moving into the flood…
Bankfull StageAn established river stage at a certain point along a river which is intended to represent the maximum safe water level which will not overflow the river…
Banner CloudA cloud plume often observed to extend downwind behind isolated mountain peaks, even on otherwise cloud-free days.
BAPSUBay Area Public Service Unit. Public Service section of the San Francisco Bay Area Weather Service Forecast Office.
Bar1. Historically, the partition separating the general public from the space occupied by the judges, lawyers and other participants in a trial. 2.
Barber Pole[Slang], a thunderstorm updraft with a visual appearance including cloud striations that are curved in a manner similar to the stripes of a barber pole.
Baroclinic leaf shieldA cloud pattern on satellite images - frequently noted in advance of formation of a low pressure center.
Baroclinic ZoneA region in which a temperature gradient exists on a constant pressure surface.
BaroclinityA measure of the state of stratification in a fluid in which surfaces of constant pressure (isobaric) intersect surfaces of constant density (isosteric).
BarogramAn analog record of pressure produced by a barograph
BarographA barometer that records its observations continuously.
BarometerAn instrument that measures atmospheric pressure.
Barometric PressureThe pressure of the atmosphere as indicated by a barometer.
Barotropic SystemA weather system in which temperature and pressure surfaces are coincident, i.e.
BarotropyThe state of a fluid in which surfaces of constant density (or temperature) are coincident with surfaces of constant pressure; it is the state of zero…
BarrageAny artificial obstruction placed in water to increase water level or divert it. Usually the idea is to control peak flow for later release.
BarrelA volumetric unit of measure for crude oil and petroleum products equivalent to 42 U.S. gallons.
Barrier JetA jet-like wind current that forms when a stably-stratified low-level airflow approaches a mountain barrier and turns to the left to blow parallel to the…
Bartel's Rotation NumberThe serial number assigned to 27-day rotation periods of solar and geophysical parameters.
BASE DATAThose digital fields of reflectivity, mean radial velocity, and spectrum width data in spherical coordinates provided at the finest resolution available…
Base FloodThe flood having a 1% chance of being equaled or exceeded in any given year.
BASE PRODUCTSThose products that present some representation of the base data. This representation may not necessarily be either in full resolution or depict the full…
Base ReflectivityOne of the three fundamental quantities (along with base [radial] velocity and spectrum width) that a Doppler radar measures.
Base StationA computer which accepts radio signals from ALERT gaging sites, decodes the data, places the data in a database, and makes the data available to other…
BaseflowStreamflow which results from precipitation that infiltrates into the soil and eventually moves through the soil to the stream channel.
Baseline Change Request (BCR)(BCR)A web-based tool that is used to discuss, review, and approve an "engineered product" or other changes to infrastructure components as it is turned over…
Baseline EmissionsThe emissions that would occur without policy intervention (in a business-as-usual scenario).
Basic solutionWater solution with more hydroxide ions (OH-) than hydrogen ions (H+); water solutions with pH greater than 7. See acid solution, alkalinity.
Basin: (1) A depression in the Earth's surface that collects sediment. (2) The area of land that drains to a particular river.
Basin BoundaryThe topographic dividing line around the perimeter of a basin, beyond which overland flow (i.e.; runoff) drains away into another basin.
Basin LagThe time it takes from the centroid of rainfall for the hydrograph to peak.
Basin RechargeRainfall that adds to the residual moisture of the basin in order to help recharge the water deficit. i.
BathymetryThe science of measuring depths of the oceans, lakes, seas, etc.
BCKGBacking- A counterclockwise shift in wind direction (for example, south winds shifting to the east).
Beach ErosionThe movement of beach materials by some combination of high waves, currents and tides, or wind.
BEAM FILLINGThe measure of variation of hydrometeor density throughout the radar sampling volume.
BEAM WIDTHAngular width of antenna pattern. Usually that width where the power density is one-half that of the axis beam. (Half-Power or 3 dB point)
Bear's Cage[Slang], a region of storm-scale rotation, in a thunderstorm, which is wrapped in heavy precipitation.
Beaufort ScaleThe Beaufort wind scale is a system used to estimate and report wind speeds when no measuring apparatus is available.
Beaver('s) Tail[Slang], a particular type of inflow band with a relatively broad, flat appearance suggestive of a beaver's tail.
Bed LoadSediment that moves by rolling or sliding along the bed and is essentially in contact with the streambed in the bed layer.
Beginning of FreezupDate on which ice forming a stable winter ice cover is first observed on the water surface.
Beginning of the BreakupDate of definite breaking, movement, or melting of ice cover or significant rise of water level.
BenchmarkA standard unit used as the basis of comparison; a universal unit that is identified with sufficient detail so that other similar classifications can be…
benthic foraminiferasingle-celled animals that live near the sediment water interface and have calcium carbonate skeletons.
Bergeron ProcessThe process by which ice crystals in a cloud grow at the expense of supercooled liquid water droplets.
Bergy BitA piece of ice which has broken away from an iceberg, extending 1-5 meters above the sea surface and 100-300 square meters in area.
Berlin MandateA ruling negotiated at the first Conference of the Parties (COP 1), which took place in March, 1995, concluding that the present commitments under the…
Bermuda HighA semi-permanent, subtropical area of high pressure in the North Atlantic Ocean off the East Coast of North America that migrates east and west with…
Best TrackA subjectively-smoothed representation of a tropical cyclone's location and intensity over its lifetime.