A diverging branch of a river which re-enters the main stream.
Beginning of the Breakup
In hydrologic terms, date of definite breaking, movement, or melting of ice cover or significant rise of water level.
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.
In hydrologic terms, the failed opening in a dam.
Waves that break, displaying white water. Depends on wave steepness and bottom bathymetry.
In hydrologic terms, the time when a river whose surface has been frozen from bank to bank for a significant portion of its length begins to change to an open water flow condition. Breakup is signaled by the breaking of the ice and often associated with ice jams and flooding.
Breakup Date
In hydrologic terms, date on which a body of water is first observed to be entirely clear of ice and remains clear thereafter.
Breakup Jam
In hydrologic terms, an ice jam that occurs as a result of the accumulation of broken ice pieces.
Breakup Period
In hydrologic terms, the period of disintegration of an ice cover.
15 to 25 mph winds
Bright Band
A distinct feature observed by a radar that denotes the freezing level of the atmosphere. The term originates from a horizontal band of enhanced reflectivity that can result when a radar antenna scans vertically through precipitation. The freezing level in a cloud contains ice particles that are coated with liquid water. These particles reflect significantly more radiation (appearing to the radar as large raindrops) than the portions of the cloud above and below the freezing layer. The bright band can affect the ability of the NEXRAD algorithms to produce accurate rainfall estimates at far ranges because the algorithm may interpret reflectivity from the bright band as an overestimate of precipitation reaching the surface.
Bright Band
The enhanced radar echo of snow as it melts to rain.
Bright Surge on the Disk (BSD)
In solar-terrestrial terms, a bright gaseous stream (surge) emanating from the chromosphere.
Bright Surge on the Limb (BSL)
In solar-terrestrial terms, a large gaseous stream (surge) that moves outward more than 0.15 solar radius above the limb.
A basic visual sensation describing the amount of light that appears to emanate from an object, or more precisely, the luminance of an object
15 to 25 mph winds
Brisk Wind Advisory
A Small Craft Advisory issued by the National Weather Service for ice-covered waters.
(Bulk Richardson Number) 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.
A method of signaling in which multiple signals share the bandwidth of the transmission by the subdivision of the bandwidth into channels based on frequency.
Brocken Specter
An optical phenomenon sometimes occurring at high altitudes when the image of an observer placed between the sun and a cloud is projected on the cloud as a greatly magnified shadow. The shadow's head is surrounded by rings of color, called a glory.
Broken Level
A layer of the atmosphere with 5/8 to 7/8 sky cover (cloud cover).
In hydrologic terms, the process of using historical data to estimate parameters in a hydrologic forecast technique such as SACSMA, routings, and unit hydrographs.
In hydrologic terms, the Dam Break Forecasting Model.
Debris Cloud
A rotating "cloud" of dust or debris, near or on the ground, often appearing beneath a condensation funnel and surrounding the base of a tornado. This term is similar to dust whirl, although the latter typically refers to a circulation which contains dust but not necessarily any debris. A dust plume, on the other hand, does not rotate. Note that a debris cloud appearing beneath a thunderstorm will confirm the presence of a tornado, even in the absence of a condensation funnel.
E-19a, Abridged Report on River Gage Sta
In hydrologic terms, an abridged version of an E-19, an E-19a updates the E-19 as additional information, or changes occur at the station during the intervening five year period. An E-19a is to be completed anytime a significant change occurs at a forecast point. An E-19a is also used to take the place of an E-19 in documenting any gage history, or information of any non-forecast point (i.e; data point).
Equilibrium Drawdown
In hydrologic terms, the ultimate, constant drawdown for a steady rate of pumped discharge.
Equilibrium Level
(EL) - On a sounding, the level above the level of free convection (LFC) at which the temperature of a rising air parcel again equals the temperature of the environment. The height of the EL is the height at which thunderstorm updrafts no longer accelerate upward. Thus, to a close approximation, it represents the height of expected (or ongoing) thunderstorm tops.
Equilibrium Surface Discharge
In hydrologic terms, the steady rate of surface discharge which results from a long-continued, steady rate of net rainfall, with discharge rate equal to net rainfall rate
Equilibrium Time
In hydrologic terms, the time when flow conditions become substantially equal to those corresponding to equilibrium discharge or equilibrium drawdown.
In solar-terrestrial terms, a linear pattern in the H-alpha chromosphere of the sun, as seen through an H-alpha filter, occurring near strong sunspots and plage or in filament channels.
Any source of heat, natural or man made, capable of igniting wildland fuels; flaming or glowing fuel particles that can be carried naturally by wind, convection currents, or gravity into unburned fuels.
Great Lakes Freeze-Up/Break-Up Outlook
(FBO) - A National Weather Service product to keep mariners informed of the projected freeze-up date or break-up date of ice on the Great Lakes.
Great Lakes Weather Broadcast
(LAWEB) - A National Weather Service product containing an observation summary prepared to provide Great Lakes mariners with a listing of weather observations along or on the Lakes.
Ice Bridge
In hydrologic terms, a continuous ice cover of limited size extending from shore to shore like a bridge.
Lake Breeze
A thermally produced wind blowing during the day from the surface of a large lake to the shore, caused by the difference in the rates of heating of the surfaces of the lake and of the land.
Land Breeze
A coastal breeze at night blowing from land to sea, caused by the difference in the rates of cooling of their respective surfaces.
Light Bridge
In solar-terrestrial terms, it is observed in white light, a bright tongue or streaks penetra- ting or crossing sunspot umbrae. The appearance of a light bridge is frequently a sign of impending region division or dissolution
Offshore Breeze
A wind that blows from the land towards a body of water. Also known as a land breeze.
Onshore Breeze
A wind that blows from a body of water towards the land. Also known as a seabreeze
In solar-terrestrial terms, the sunspot area that may surround the darker umbra or umbrae. It consists of linear bright and dark elements radial from the sunspot umbra.
Sea Breeze
A thermally produced wind blowing during the day from a cool ocean surface onto the adjoining warm land, caused by the difference in the rates of heating of the surfaces of the ocean and of the land.
Sea Breeze Convergence Zone
The zone at the leading edge of a sea breeze where winds converge. The incoming air rises in this zone, often producing convective clouds.
Sea Breeze Front
The leading edge of a sea breeze, whose passage is often accompanied by showers, a wind shift, or a sudden drop in temperature.
Sectorized Hybrid Scan
A single reflectivity scan composed of data from the lowest four elevation scans. Close to the radar, higher tilts are used to reduce clutter. At further ranges, either the maximum values from the lowest two scans are used or the second scan values are used alone.
Sphere Calibration
Reflectivity calibration of a radar by pointing the dish at a metal sphere of (theoretically) known reflectivity. The sphere is often tethered to a balloon.
The bending of the radar beam in the vertical which is less than under standard refractive conditions. This causes the beam to be higher than indicated, and lead to the underestimation of cloud heights.
Tropical Analysis and Forecast Branch
One of three branches of the Tropical Prediction Center (TPC). It provides year-round products involving marine forecasting, aviation forecasts and warnings (SIGMETs), and surface analyses. The unit also provides satellite interpretation and satellite rainfall estimates for the international community. In addition, TAFB provides support to NHC through manpower and tropical cyclone intensity estimates from the Dvorak technique.
In solar-terrestrial terms, the dark core or cores (umbrae) in a sunspot with penumbra, or a sunspot lacking penumbra.

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