Subj : Weather Terms (B) Part 1
To : All
From : Daryl Stout
Date : Thu Nov 03 2016 12:06 am
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).
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