This weather glossary contains information on more than 2000 terms,
phrases and abbreviations used by the National Weather Service (NWS)...
the government agency who makes weather forecasts, and issues weather advisories, watches, and warnings, for the United States, and its
territories.

Many of these terms and abbreviations are used by NWS forecasters to communicate between each other and have been in use for many years and
before many NWS products were directly available to the public. It is the purpose of this glossary to aid you in better understanding NWS products.

***

B
Abbreviation used on long-term climate outlooks issued by CPC to indicate
areas that are likely to be below normal for a given parameter
(temperature, precipitation, etc.).

Back Door Cold Front
A cold front moving south or southwest along the Atlantic seaboard and
Great Lakes; these are especially common during the spring months.

Back-building Thunderstorm
A thunderstorm in which new development takes place on the upwind side
(usually the west or southwest side), such that the storm seems to remain stationary or propagate in a backward direction.

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 weather potential.

Backfire
A fire started to stop an advancing fire by creating a burned area in its
path.

Backflow
In hydrologic terms, the backing up of water through a conduit or channel
in the direction opposite to normal flow.

Backing
(abbrev. BCKG)- A counterclockwise shift in wind direction (for example,
south winds shifting to the east).

Backing Winds
Winds which shift in a counterclockwise direction with time at a given
location (e.g. from southerly to southeasterly), or change direction in
a counterclockwise sense with height (e.g. westerly at the surface but
becoming more southerly aloft). The opposite of veering winds.

In storm spotting, a backing wind usually refers to the turning of a
south or southwest surface wind with time to a more east or southeasterly direction. Backing of the surface wind can increase the potential for
tornado development by increasing the directional shear at low levels.

Backsight
In hydrologic terms, a rod reading taken on a point of known elevation,
a benchmark or a turning point. Backsights are added to the known
elevation to arrive at the height of the instrument. With a known
height of the instrument, the telescope can be used to determine the
elevation of other points in the vicinity.

Backwater Curve
In hydrologic terms, the 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 to the depth of water having been increased
by the interposition of an obstruction such as a dam or weir. The term is sometimes used in a generic sense to denote all water surface profiles;
or for profiles where the water is flowing at depths greater than the
critical.

Backwater Effect
In hydrologic terms, the effect which a dam or other obstruction has in
raising the surface of the water upstream from it.

Backwater Flooding
Hydrologic terms, upstream flooding caused by downstream conditions such
as channel restriction and/or high flow in a downstream confluence stream.

Bandwidth
The frequency range between the lowest and highest frequencies that are
passed through a component, circuit, or system with acceptable
attenuation.

Bank
In hydrologic terms, the margins of a channel. Banks are called right or
left as viewed facing in the direction of the flow.

Bank Storage
In hydrologic terms, water absorbed and stored in the void in the soil
cover in the bed and banks of a stream, lake, or reservoir, and returned
in whole or in part as the level of water body surface falls.

Bankfull
The 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 plain.

Bankfull Stage
An 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 banks or cause any significant damage within the
reach of the river.

Banner Cloud
A cloud plume often observed to extend downwind behind isolated mountain
peaks, even on otherwise cloud-free days.

BAPSU
Bay Area Public Service Unit. Public Service section of the San Francisco
Bay Area Weather Service Forecast Office.

Bar
An obstacle formed at the shallow entrance to the mouth of a river or bay.

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. 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.

Baroclinic leaf shield
A cloud pattern on satellite images - frequently noted in advance of
formation of a low pressure center.

Baroclinic Zone
A region in which a temperature gradient exists on a constant pressure
surface. Baroclinic zones are favored areas for strengthening and
weakening systems; barotropic systems, on the other hand, do not exhibit significant changes in intensity. Also, wind shear is characteristic of
a baroclinic zone.

Baroclinity
A measure of the state of stratification in a fluid in which surfaces of constant pressure (isobaric) intersect surfaces of constant density (isosteric).

Barogram
An analog record of pressure produced by a barograph

Barograph
A barometer that records its observations continuously.

Barometer
An instrument that measures atmospheric pressure.

Barometric Pressure
The pressure of the atmosphere as indicated by a barometer.

Barotropic System
A weather system in which temperature and pressure surfaces are
coincident, i.e., temperature is uniform (no temperature gradient) on a constant pressure surface. Barotropic systems are characterized by a
lack of wind shear, and thus are generally unfavorable areas for severe thunderstorm development. See baroclinic zone.

Usually, in operational meteorology, references to barotropic systems
refer to equivalent barotropic systems - systems in which temperature
gradients exist, but are parallel to height gradients on a constant
pressure surface. In such systems, height contours and isotherms are
parallel everywhere, and winds do not change direction with height.

As a rule, a true equivalent barotropic system can never be achieved in
the real atmosphere. While some systems (such as closed lows or cutoff
lows) may reach a state that is close to equivalent barotropic, the term barotropic system usually is used in a relative sense to describe
systems that are really only close to being equivalent barotropic, i.e., isotherms and height contours are nearly parallel everywhere and
directional wind shear is weak.

Barotropy
The 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 baroclinity.

Barrage
In hydrologic terms, any artificial obstruction placed in water to
increase water level or divert it. Usually the idea is to control peak
flow for later release.

Barrier Jet
A 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 longitudinal axis of the barrier.

Bartel's Rotation Number
The serial number assigned to 27-day rotation periods of solar and
geophysical parameters. Rotation 1 in this sequence was assigned
arbitrarily by Bartel to begin in January 1833.

Base Flood
In hydrologic terms, the national standard for floodplain management is
the base, or one percent chance flood. This flood has at least one
chance in 100 of occurring in any given year. It is also called a 100
year flood.

Base Reflectivity
One of the three fundamental quantities (along with base [radial]
velocity and spectrum width) that a Doppler radar measures. Reflectivity
is related to the power, or intensity, of the reflected radiation that
is sensed by the radar antenna. Base reflectivity is expressed on a
logarithmic scale in units called dBZ. The term "base" refers to the
product being "basic", with little advanced processing performed on the
data. Base reflectivity is related to rainfall intensity (e.g., drop
size and rainfall rate) and hail size (for large values of reflectivity).

Base Station
In hydrologic terms, a 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 users.

Base Width
In hydrologic terms, the time duration of a unit hydrograph.

Baseflow
In hydrologic terms, streamflow which results from precipitation that infiltrates into the soil and eventually moves through the soil to the
stream channel. This is also referred to as ground water flow, or
dry-weather flow.

Basin
An area having a common outlet for its surface runoff. Also called a
"Drainage Basin."

Basin Boundary
The topographic dividing line around the perimeter of a basin, beyond
which overland flow (i.e.; runoff) drains away into another basin.

Basin Lag
In hydrologic terms, the time it takes from the centroid of rainfall for
the hydrograph to peak.

Basin Recharge
In hydrologic terms, rainfall that adds to the residual moisture of the
basin in order to help recharge the water deficit. i.e; water absorbed
into the soil that does not take the form of direct runoff.

Bathymetry
The science of measuring depths of the oceans, lakes, seas, etc.

BCKG
Backing- A counterclockwise shift in wind direction (for example, south
winds shifting to the east).

BCM
Become

BCMNG
Becoming

BD
Blowing Dust

Beach Erosion
The movement of beach materials by some combination of high waves,
currents and tides, or wind.

Bear's Cage
[Slang], a region of storm-scale rotation, in a thunderstorm, which is
wrapped in heavy precipitation. This area often coincides with a radar
hook echo and/or mesocyclone, especially one associated with an HP
storm. The term reflects the danger involved in observing such an area visually, which must be done at close range in low visibility.

Beaufort Scale
The Beaufort wind scale is a system used to estimate and report wind
speeds when no measuring apparatus is available. It was invented in the
early 19th Century by Admiral Sir Francis Beaufort of the British Navy
as a way to interpret winds from conditions at sea. Since that time, the
scale has been modernized for effects on land.

Beaufort Force 0 - Wind less than 1 kt, Calm, Sea surface smooth and mirror-like. Smoke rises vertically.

Beaufort Force 1 - Wind 1-3 kt, Light Air, Scaly ripples, no foam crests.
Smoke drift indicates wind direction, still wind vanes.

Beaufort Force 2 - Wind 4-6 kt, Light Breeze, Small wavelets, crests
glassy, no breaking waves. Wind felt on face, leaves rustle, vanes begin
to move.

Beaufort Force 3 - Wind 7-10 kt, Gentle Breeze, Large wavelets, crests
begin to break, scattered whitecaps. Leaves and small twigs constantly
moving, light flags extended.

Beaufort Force 4 - Winds 11-16 kt, Moderate Breeze, Small waves 1-4 ft. becoming longer, numerous whitecaps. Dust, leaves, and loose paper
lifted, small tree branches move.

Beaufort Force 5 - Winds 17-21 kt, Fresh Breeze, Moderate waves 4-8 ft
taking longer form, many whitecaps, some spray. Small trees in leaf
begin to sway.

Beaufort Force 6 - Winds 22-27 kt, Strong Breeze, Larger waves 8-13 ft, whitecaps common, more spray. Larger tree branches moving, whistling
in wires.

Beaufort Force 7 - Winds 28-33 kt, Near Gale, Sea heaps up, waves 13-20
ft, white foam streaks off breakers. Whole trees moving, resistance felt walking against wind.

Beaufort Force 8 - Winds 34-40 kt Gale, Moderately high (13-20 ft)
waves of greater length, edges of crests begin to break into spindrift,
foam blown in streaks. Whole trees in motion, resistance felt walking
against wind.

Beaufort Force 9 - Winds 41-47 kt, Strong Gale, High waves (20 ft), sea
begins to roll, dense streaks of foam, spray may reduce visibility.
Slight structural damage occurs, slate blows off roofs.

Beaufort Force 10 - Winds 48-55 kt, Storm, Very high waves (20-30 ft)
with overhanging crests, sea white densely blown foam, heavy rolling,
lowered visibility. Seldom experienced on land, trees broken or uprooted, "considerable structural damage".

Beaufort Force 11 - Winds 56-63 kt, Violent Storm, Exceptionally high
(30-45 ft) waves, foam patches cover sea, visibility more reduced.

Beaufort Force 12 -Winds 64+ kt, Hurricane, Air filled with foam, waves
over 45 ft, sea completely white with driving spray, visibility greatly reduced.

Beaver('s) Tail
[Slang], a particular type of inflow band with a relatively broad, flat appearance suggestive of a beaver's tail. It is attached to a supercell's general updraft and is oriented roughly parallel to the pseudo-warm front, i.e., usually east to west or southeast to northwest. As with any inflow
band, cloud elements move toward the updraft, i.e., toward the west or northwest. Its size and shape change as the strength of the inflow
changes. See also inflow stinger.

Bed Load
In hydrologic terms, sand, silt, gravel, or soil and rock detritus
carried by a stream on or immediately above its bed. The particles of
this material have a density or grain size such as to preclude movement
far above or for a long distance out of contact with the stream bed
under natural conditions of flow.

Beginning of Freezup
In hydrologic terms, date on which ice forming a stable winter ice cover
is first observed on the water surface.

Beginning of the Breakup
In hydrologic terms, date of definite breaking, movement, or melting of
ice cover or significant rise of water level.

Benchmark
(Abbrev. BM) - In hydrologic terms, a permanent point whose known
elevation is tied to a national network. These points are created to
serve as a point of reference. Benchmarks have generally been
established by the USGS, but may have been established by other Federal
or local agencies. Benchmarks can be found on USGS maps.

Bergeron Process
The process by which ice crystals in a cloud grow at the expense of
supercooled liquid water droplets.

Bergy Bit
A 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. Can
also be the remains of a melting iceberg.

Bermuda High
A 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 varying central pressure. Depending on the season, it
has different names. When it is displaced westward, during the
Northern Hemispheric summer and fall, the center is located in the
western North Atlantic, near Bermuda. In the winter and early spring,
it is primarily centered near the Azores in the eastern part of the
North Atlantic. Also known as Azores High.

Best Track
A subjectively-smoothed representation of a tropical cyclone's location
and intensity over its lifetime. The best track contains the cyclone's latitude, longitude, maximum sustained surface winds, and minimum
sea-level pressure at 6-hourly intervals. Best track positions and
intensities, which are based on a post-storm assessment of all available
data, may differ from values contained in storm advisories. They also
generally will not reflect the erratic motion implied by connecting
individual center fix positions.

BFR
Before

BGN
Begin

BHND
Behind

Billow Cloud
A cloud consisting of broad parallel bands oriented perpendicular to the
wind.

BINOVC
Breaks in Overcast

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.

Breakers
Waves that break, displaying white water. Depends on wave steepness and
bottom bathymetry.

Breakup
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.

Breezy
15 to 25 mph winds.

BRF
Brief

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 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.

Brightness
A basic visual sensation describing the amount of light that appears to
emanate from an object, or more precisely, the luminance of an object.

Brisk
15 to 25 mph winds.

Brisk Wind Advisory
A Small Craft Advisory issued by the National Weather Service for
ice-covered waters.

BRK
Break

BRN
(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.

Broadband
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).

BS
Blowing Snow

BTR
Better

BTWN
Between

Bubble High
A mesoscale area of high pressure, typically associated with cooler air
from the rainy downdraft area of a thunderstorm or a complex of
thunderstorms. A gust front or outflow boundary separates a bubble high
from the surrounding air.

Bubbler Gage
In hydrologic terms, a water stage recording device that is capable of attaching to a LARC for data automation purposes.

BUFKIT
A software tool used by forecasters to examine the vertical profile and
other aspects of the atmosphere.

Bulk Richardson Number
A non-dimensional (i.e., no units) number relating vertical stability to 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.

Buoyancy
The tendency of a body to float or to rise when submerged in a fluid; the
power of a fluid to exert an upward force on a body placed in it.

Burst
In solar-terrestrial terms, a transient enhancement of the solar radio emission, usually associated with an active region or flare.

Bust
Slang for an inaccurate forecast, especially one where significant
weather (e.g., heavy snowfall) is predicted but does not occur.

Buttress Dam
Buttress dams are comprised of reinforced masonry or stonework built a
gainst concrete. They are usually in the form of flat decks or multiple
arches. They require about 60 percent less concrete than gravity dams,
but the increased form work and reinforcement steel required usually
offset the savings in concrete. Many were built in the 1930's when the
ratio of labor cost to materials was comparatively low. However, this
type of construction is not competitive with other types of dams when
labor costs are high.

BWER
Abbreviation for Bounded Weak Echo Region; a 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.

BYD
Beyond
--- SBBSecho 3.13-Win32
* Origin: The Thunderbolt BBS - tbolt.synchro.net (618:250/33)