Sky condition
when between 3/10 and 7/10 of the sky is covered. Used more frequently
at night.
| PARTLY
SUNNY |
Similar
to partly cloudy. Used to emphasize daytime sunshine. |
| PATCHES |
Used
with fog to denote random occurrence over relatively small areas. |
| PENDANT
ECHO |
Radar
signature generally similar to a hook echo, except that the hook shape
is not as well defined. |
| POLAR
VORTEX |
A circumpolar
wind circulation which isolates the Antarctic continent during the
cold Southern Hemisphere winter, heightening ozone depletion. |
| POP |
Probability
Of Precipitation. Probability forecasts are subjective
estimates of the chances of encountering measurable precipitation
at some time during the forecast period. |
| POSITIVE
AREA |
The area
on a sounding representing the layer in which a lifted parcel would
be warmer than the environment; thus, the area between the environmental
temperature profile and the path of the lifted parcel. |
| POSITIVE-TILE
TROUGH |
An upper
level system which is tilted to the east with increasing latitude
(i.e., from southwest to northeast). A positive-tilt trough often
is a sign of a weakening weather system, and generally is less likely
to result in severe weather than a negative-tilt trough if all other
factors are equal. |
| POTENTIAL
TEMPERATURE |
The temperature
a parcel of dry air would have if brought adiabatically (i.e., without
transfer of heat or mass) to a standard pressure level of 1000 mb. |
| PRECIPITATION |
Liquid
or solid water molecules that fall from the atmosphere and reach the
ground. |
| PRESSURE |
The force
exerted by the interaction of the atmosphere and gravity. Also known
as atmospheric pressure. |
| PRESSURE
CHANGE |
The net
difference between pressure readings at the beginning and ending of
a specified interval of time. |
| PRESSURE
FALLING RAPIDLY |
A decrease
in station pressure at a rate of 0.06 inch of mercury or more per
hour which totals 0.02 inch or more. |
| PRESSURE
GRADIENT |
The rate
of decrease of pressure with distance at a fixed level. |
| PRESSURE
GRADIENT FORCE |
Force
acting on air that causes it to move from areas of higher pressure
to areas of lower pressure. |
| PRESSURE
RISING RAPDILY |
An increase
in station pressure at a rate of 0.06 inch of mercury or more per
hour which totals 0.02 inch or more. |
| PRESSURE
TENDENCY |
The character
and amount of atmospheric pressure change during a specified period
of time, usually the 3-hour period preceding an observation. |
| PRESSURE
UNSTEADY |
A pressure
that fluctuates by 0.03 inch of mercury or more from the mean pressure
during the period of measurement. |
| PREVAILING
WESTERLIES |
Winds
in the middle latitudes (approximately 30 degrees to 60 degrees) that
generally blow from west to east. |
| PREVAILING
WIND |
The direction
from which the wind blows most frequently in any location. |
| PROFILER |
An instrument
designed to measure horizontal winds directly above its location,
and thus measure the vertical wind profile. Profilers operate on the
same principles as Doppler radar. |
| PSYCHROMETER |
An instrument
used for measuring the water vapor content of the atmosphere. It consists
of two thermometers, one of which is an ordinary glass thermometer,
while the other has its bulb covered with a jacket of clean muslin
which is saturated with distilled water prior to use. |
| PULSE
STORM |
A thunderstorm
within which a brief period (pulse) of strong updraft occurs, during
and immediately after which the storm produces a short episode of
severe weather. These storms generally are not tornado producers,
but often produce large hail and/or damaging winds. See overshooting
top, cyclic storm. |
| PVA |
Positive
Vorticity Advection. Advection of higher values of vorticity
into an area, which often is associated with upward motion (lifting)
of the air. PVA typically is found in advance of disturbances aloft
(i.e., shortwaves), and is a property which often enhances the potential
precipitation. |
| Q |
|
| QPF |
Quantitative
Precipitation Forecast |
| R |
|
| RADAR |
An instrument
used to detect precipitation by measuring the strength of the electromagnetic
signal reflected back. RADAR = RAdio Detection And Ranging. |
| RADIATION |
Energy
emitted in the form of electromagnetic waves. Radiation has differing
characteristics depending upon the wavelength. Radiation from the
Sun has a short wavelength (ultra-violet) while energy re-radiated
from the Earth's surface and the atmosphere has a long wavelength
(infra-red). |
| RADIATION
FOG |
Fog produced
over the land by the cooling of the lower atmosphere as it comes in
contact with the ground. Also known as ground fog. |
| RADIATIONAL
COOLING |
Cooling
process of the Earth's surface and adjacent air, which occurs when
infrared (heat) energy radiates from the surface of the Earth upward
through the atmosphere into space. Air near the surface transfers
its thermal energy to the nearby ground through conduction, so that
radiative cooling lowers the temperature of both the surface and the
lowest part of the atmosphere. |
| RADIOSONDE |
An instrument
attached to a weather balloon that transmits pressure, humidity, temperature,
and winds as it ascends. |
| RAIN |
Liquid
water droplets that fall from the atmosphere, having diameters greater
than drizzle. |
| RAIN-FREE
BASE |
A horizontal,
dark cumulonimbus base that has no visible precipitation beneath it.
This structure usually marks the location of the thunderstorm updraft.
Tornadoes most commonly develop (1) from wall clouds that are attached
to the rain-free base, or (2) from the rain-free base itself. This
is particularly true when the rain-free base is observed to the south
or southwest of the precipitation shaft. |
| RAINBOW |
Optical
phenomenon when light is refracted and reflected by moisture in the
air into concentric arcs of color. |
| RAWINSONDE |
A balloon
that is tracked by radar to measure wind speeds and wind directions
in the atmosphere. |
| REFLECTIVITY |
Radar
term referring to the ability of a radar target to return energy;
used to estimate precipitation intensity and rainfall rates. |
| REFRACTION |
The bending
of light as it passes through areas of different density, such as
from air through ice crystals. |
| RELATIVE
HUMIDITY |
The amount
of water vapor in the air, compared to the amount the air could hold
if it was totally saturated. (Expressed as a percentage). |
RETROGRESSION
(or RETROGRADE MOTION) |
Movement
of a weather system in a direction opposite to that of the basic flow
in which it is embedded, usually referring to a closed low or a longwave
trough which moves westward. |
| RETURN
FLOW |
South
winds on the back (west) side of an eastward-moving surface high pressure
system. Return flow over the central and eastern United States typically
results in a return of moist air from the Gulf of Mexico (or the Atlantic
Ocean). |
| RFC |
River
Forecast Center. The Arkansas-Red Basin River Forecast
Center is located in Tulsa, OK. |
| RIDGE |
An elongated
area of high pressure at the surface or aloft. |
RIGHT
ENTRANCE REGION
(or RIGHT READ QUADRANT) |
The area
upstream from and to the right of an upper-level jet max (as would
be viewed looking along the direction of flow). Upward motion and
severe thunderstorm potential sometimes are increased in this area
relative to the wind speed maximum. |
| RIGHT
MOVER |
A thunderstorm
that moves appreciably to the right relative to the main steering
winds and to other nearby thunderstorms. Right movers typically are
associated with a high potential for severe weather. (Supercells often
are right movers.) |
| ROLL
CLOUD |
A relatively
rare, low-level horizontal, tube-shaped accessory cloud completely
detached from the cumulonimbus base. When present, it is located along
the gust front and most frequently observed on the leading edge of
a line of thunderstorms. The roll cloud will appear to be slowly "rolling"
about its horizontal axis. Roll clouds are not and do not produce
tornadoes. |
| ROPE
(or ROPE FUNNEL) |
A narrow,
often contorted condensation funnel usually associated with the decaying
stage of a tornado. |
| ROPE
CLOUD |
In satellite
meteorology, a narrow, rope-like band of clouds sometimes seen on
satellite images along a front or other boundary. |
| ROPE
STAGE |
The dissipating
stage of a tornado, characterized by thinning and shrinking of the
condensation funnel into a rope (or rope funnel). Damage still is
possible during this stage. |
| RUC |
Rapid
Update Cycle, a numerical model run at NCEP that focuses
on short-term (up to 12 h) forecasts and small-scale (mesoscale) weather
features. Forecasts are prepared every 3 hours for the contiguous
United States. |
| S |
|
| SCATTERED
CLOUDS |
Sky condition
when between 1/10 and 5/10 of the sky is covered. |
| SCUD
CLOUDS |
Small,
ragged, low cloud fragments that are unattached to a larger cloud
base and often seen with and behind cold fronts and thunderstorm gust
fronts. Such clouds generally are associated with cool moist air,
such as thunderstorm outflow. |
| SEA-LEVEL
PRESSURE |
The pressure
value obtained by the theoretical reduction or increase of barometric
pressure to sea-level. |
| SEVERE
THUNDERSTORM |
A strong
thunderstorm with wind gusts in excess of 58 mph (50 knots) and/or
hail with a diameter of 3/4" or more. |
| SEVERE
THUNDERSTORM WARNING |
Issued
when thunderstorms are expected to have wind gusts to 58 mph or above
or hail 3/4 inch or more in diameter. |
| SEVERE
THUNDERSTORM WATCH |
Issued
when conditions are favorable for the development of severe thunderstorms
in and close to a defined area. |
| SHELF
CLOUD |
Long,
wedge-shaped clouds associated with the gust front. Shelf clouds indicate
the downdraft or outflow of a thunderstorm. |
| SHEAR
(WIND SHEAR) |
Variation
in wind speed and/or direction over a short distance. Shear usually
refers to vertical wind shear, i.e., the change in wind with height,
but the term also is used in Doppler radar to describe changes in
radial velocity over short horizontal distances. |
| SHORT-FUSE
WARNING |
A warning
issued by the NWS for a local weather hazard of relatively short duration.
Short-fuse warnings include tornado warnings, severe thunderstorm
warnings, and flash flood warnings. Tornado and severe thunderstorm
warnings typically are issued for periods of an hour or less, flash
flood warnings typically for three hours or less. |
| SHORTWAVE
(SHORTWAVE TROUGH) |
A disturbance
in the mid or upper part of the atmosphere which induces upward motion
ahead of it. If other conditions are favorable, the upward motion
can contribute to thunderstorm development ahead of a shortwave. |
| SHOWER |
Precipitation
that is intermittent, in space, time, or intensity. |
| SKY
CONDITION |
The state
of the sky in terms of such parameters as sky cover, layers and associated
heights, ceiling, and cloud types. |
| SKY
COVER |
The amount
of the sky which is covered by clouds or obscurations in contact with
the surface. |
| SLEET |
A type
of frozen precipitation, consisting of small transparent ice pellets. |
SLIGHT
RISK
(of severe thunderstorms) |
Severe
thunderstorms are expected to affect between 2 and 5 percent of the
area. A slight risk generally implies that severe weather events are
expected to be isolated. |
| SLING
PSYCHROMETER |
A psychrometer
in which the wet and dry bulb thermometers are mounted upon a frame
connected to a handle. The psychrometer may be whirled by hand in
order to provided the necessary ventilation. |
| SLIGHT
CHANCE |
In probability
of precipitation statements, usually equivalent to a 20 percent chance. |
| SNOW |
Frozen
precipitation composed of ice particles in complex hexagonal patterns. |
| SNOW
FLURRIES |
Light
snow showers, usually of an intermittent nature with no measurable
accumulation. |
| SOUNDING |
A plot
of the vertical profile of temperature and dew point (and often winds)
above a fixed location ( example). Soundings are used extensively
in weather forecasting, e.g., to determine instability, locate temperature
inversions etc. |
| SOUTHERN
OSCILLATION |
A periodic
reversal of the pressure pattern across the tropical Pacific Ocean
during El Nino events. |
| SPC |
Storm
Prediction Center. Located in Norman, OK. This office
is responsible for monitoring and forecasting severe convective weather
in the continental U.S. This includes the issuance of Tornado and
Severe Thunderstorm Watches. |
| SPEED
SHEAR |
The component
of wind shear which is due to a change in wind speed with height,
e.g., southwesterly winds of 20 mph at 10,000 feet increasing to 50
mph at 20,000 feet. Speed shear is an important factor in severe weather
development, especially in the middle and upper levels of the atmosphere. |
| SPIN-UP |
A small-scale
vortex initiation, such as what may be seen when a gustnado, landspout,
or suction vortex forms. |
| SQUALL
LINE |
A non-frontal
band or line of thunderstorms. |
| STABILITY |
An indication
of how easily a parcel of air is lifted. If the air is very stable
it is difficult to make the parcel rise. If the air is very unstable
the parcel may rise on its own once started. |
| STABLE
AIR |
Air with
little or no tendency to rise, that is usually accompanied by clear
dry weather. |
| STATEMENT |
Provides
the public with information concerning the status of existing warnings. |
| STATION
INDENTIFIER |
A group
of four alphabetic characters used to identify a location that makes
weather observations. |
| STATION
PRESSURE |
The pressure
that is read from a barometer but is not adjusted to sea level. |
| STATIONARY
FRONT |
A transition
zone between air masses, with neither advancing upon the other. |
STEERING
WINDS
(Steering Currents) |
A prevailing
synoptic scale flow which governs the movement of smaller features
embedded within it. |
| STORM
TRACK |
The path
that a low pressure area follows. |
| STORM-RELATIVE |
Measured
relative to a moving thunderstorm, usually referring to winds, wind
shear, or helicity. |
| STORM-SCALE |
Referring
to weather systems with sizes on the order of individual thunderstorms.
See synoptic scale, mesoscale. |
| STRAIGHT
LINE WINDS |
Thunderstorm
winds most often found with the gust front. They originate from downdrafts
and can cause damage which occurs in a "straight line", as opposed
to tornadic wind damage which has circular characteristics. |
| STRATIFORM |
Having
extensive horizontal development, as opposed to the more vertical
development characteristic of convection. Stratiform clouds cover
large areas but show relatively little vertical development. |
| STRATOCUMULUS |
Low-level
clouds, existing in a relatively flat layer but having individual
elements. Elements often are arranged in rows, bands, or waves. |
| STRATOSPHERE |
The layer
of the atmosphere above the troposphere, where temperature increases
with height. |
| STRATUS |
Flat
low level clouds. |
| STRIATIONS |
Grooves
or channels in cloud formations, arranged parallel to the flow of
air and therefore depicting the airflow relative to the parent cloud.
|
| SUBLIMATION |
The change
from ice directly to water vapor or from water vapor to ice with out
going through the liquid water phase. |
| SUBSIDENCE |
Sinking
air that is associated with warming air and little cloud formation. |
| SUBTROPICAL
JET |
The branch
of the jet stream that is found in the lower latitudes. |
SUCTION
VORTEX
(sometimes SUCTION SPOT) |
A small
but very intense vortex within a tornado circulation. Several suction
vortices typically are present in a multiple-vortex tornado. Much
of the extreme damage associated with violent tornadoes (F4 and F5
on the Fujita scale) is attributed to suction vortices. |
| SUPERCELL |
A highly
organized thunderstorm with a rotating updraft, known as a mesocyclone.
It poses an inordinately high threat to life and property. Often produces
large hail, strong winds, and tornadoes. |
| SUPERCOOLED
WATER |
Water
that stays in liquid form if undisturbed even though it has been cooled
to a temperature below its normal freezing point. |
| SUPERSATURATION |
The condition
which occurs in the atmosphere when the relative humidity is greater
than 100 percent. |
| SURFACE
PRESSURE |
The pressure
that is read from a barometer but is not adjusted to sea level. |
| SUSTAINED
WINDS |
The wind
speed obtained by averaging the observed values over a one minute
period. |
| SWEAT
INDEX |
Severe
Weather ThrEAT index. A stability index developed by
the Air Force which incorporates instability, wind shear, and wind
speeds. |
| SYNOPTIC
CHART |
Chart
showing meteorological conditions over a region at a given time; weather
map. |
| SYNOPTIC
SCALE (LARGE SCALE) |
Size
scale referring generally to weather systems with horizontal dimensions
of several hundred miles or more. Most high and low pressure areas
seen on weather maps are synoptic-scale systems. Compare with mesoscale. |
| T |
|
| TAF |
A weather
forecast for aircraft operations at an airport. |
| TELECONNECTION |
A strong
statistical relationship between weather in different parts of the
globe. For example, there appears to be a teleconnection between the
tropics and North America during El Niņo. |
| THERMAL |
Small
rising column of air due to surface heating. |
| THERMODYNAMICS |
In general,
the relationships between heat and other properties (such as temperature,
pressure, density, etc.) In forecast discussions, thermodynamics usually
refers to the distribution of temperature and moisture (both vertical
and horizontal) as related to the diagnosis of atmospheric instability. |
THETA-E
(or Equivalent Potential Temperature) |
The temperature
a parcel of air would have if a) it was lifted until it became saturated,
b) all water vapor was condensed out, and c) it was returned adiabatically
(i.e., without transfer of heat or mass) to a pressure of 1000 millibars. |
| THETA-E
RIDGE |
An axis
of relatively high values of theta-e. Severe weather and excessive
rainfall often occur near or just upstream from a theta-e ridge. |
| THUNDER |
The sound
wave produced as a lightning stroke heats the air causing it to rapidly
expand. |
| THUNDERSTORM |
A storm
with lightning and thunder, produced by a cumulonimbus cloud, and
usually associated with gusty winds, heavy rain, and sometimes hail
and tornadoes. |
TILTED
STORM
or TILTED UPDRAFT |
A thunderstorm
or cloud tower which is not purely vertical but instead exhibits a
slanted or tilted character. It is a sign of vertical wind shear,
a favorable condition for severe storm development. |
| TOPOGRAPHY |
Generally,
the lay-out of the major natural and man-made physical features of
the earth's surface. Bridges, highways, trees, rivers and fields are
all components that make up this topography. |
| TORNADO |
A violently
rotating column of air below the base of a thunderstorm, and in contact
with the ground. A tornado does not require the visible presence of
a condensation funnel cloud. |
| TORNADO
ALLEY |
The area
of the United States in which tornadoes are most frequent. It encompasses
the great lowland areas of the Mississippi, the Ohio, and lower Missouri
River Valleys. Although no state is entirely free of tornadoes, they
are most frequent in the Plains area between the Rocky Mountains and
Appalachians. |
| TORNADO
FAMILY |
A series
of tornadoes produced by a single supercell, resulting in damage path
segments along the same general line. |
| TORNADO
WARNING |
Issued
when there is likelihood of a tornado within the given area based
on radar or actual sighting. It is usually accompanied by conditions
indicated for Severe Thunderstorm Warning. |
| TOTOAL-TOTALS
INDEX |
A stability
index and severe weather forecast tool, equal to the temperature at
850 mb plus the dew point at 850 mb, minus twice the temperature at
500 mb. |
| TOWERING
CUMULUS |
A large
cumulus cloud with great vertical development, usually with a cauliflower-like
appearance, but lacking the characteristic anvil shaped top of a Cb.
(Often shortened to "towering cu," and abbreviated TCU.) |
| TRACE |
Precipitation
amounts less than 0.01". |
| TRADE
WINDS |
Persistent
low-level tropical winds that blow from the subtropical high pressure
centers towards the equatorial low. |
| TRIPLE
POINT |
The intersection
point between two boundaries (dry line, outflow boundary, cold front,
warm front etc.), often a focus for thunderstorm development. |
| TROPICAL
DEPRESSION |
Tropical
mass of thunderstorms with a cyclonic wind circulation and winds between
20 and 34 knots. |
| TROPICAL
DISTURBANCE |
An organized
mass of tropical thunderstorms, with a slight cyclonic circulation
and winds less than 20 knots. |
| TROPICAL
STORM |
An organized
cyclone in the tropics with wind speed between 35 and 64 knots. |
| TROPOPAUSE |
The boundary
between troposphere and the stratosphere. It is usually characterized
by an abrupt change in temperature with height from positive (decreasing
temperature with height) to neutral or negative (temperature constant
or increasing with height). |
| TROPOSPHERE |
The lowest
layer of the atmosphere where the temperature decreases with height.
Most of earth's weather occurs in this layer. |
| TROUGH |
An elongated
area of low pressure at the surface or aloft. |
| TURBULENCE |
Disrupted
flow in the atmosphere that produces gusts and eddies. |
| TVS |
Tornadic
Vortex Signature. Doppler radar signature in the radial
velocity field indicating intense, concentrated rotation - more so
than a mesocyclone. |
| U |
|
| UKMET
| United
Kingdom forecast model. |
| ULTRAVIOLET
RADIATION |
The energy
range just beyond the violet end of the visible spectrum. Although
ultraviolet radiation constitutes only about 5 percent of the total
energy emitted from the sun, it is the major energy source for the
stratosphere and mesosphere, playing a dominant role in both energy
balance and chemical composition. |
| UNSTABLE
AIR |
Air that
rises easily and can form clouds and rain. |
| UPDRAFT |
A small-scale
current of rising air. This is often associated with cumulus and cumulonimbus
clouds. |
| UPPER
LEVEL SYSTEM |
A general
term for any large-scale or mesoscale disturbance capable of producing
upward motion (lift) in the middle or upper parts of the atmosphere. |
| UPSLOPE
FLOW |
Air that
flows toward higher terrain, and hence is forced to rise. The added
lift often results in widespread low cloudiness and stratiform precipitation
if the air is stable, or an increased chance of thunderstorm development
if the air is unstable. |
| UPSTREAM |
Toward
the source of the flow, or located in the area from which the flow
is coming. |
| UTC |
Coordinated
Universal Time. The time in the zero degree meridian time zone. |
| UVI |
Ultraviolet
Index |
| UVV |
Upward
Vertical Velocity. |
| V |
|
| VAPOR
PRESSURE |
The pressure
exerted by water vapor molecules in a given volume of air. |
| VARIABLE
CEILING |
A ceiling
of less than 3,000 feet which rapidly increases or decreases in height
by established criteria during the period of observation. |
| VEERING
WIND |
Wind
which changes in a clockwise direction with time at a given location
(e.g., from southerly to westerly), or which change direction in a
clockwise sense with height (e.g., southeasterly at the surface turning
to southwesterly aloft). Veering winds with height are indicative
of warm air advection (WAA). |
| VERTICAL
SHEAR |
The rate
of change of wind speed or direction, with a given change in height. |
| VERTICALLY-STACKED
SYSTEM |
A low-pressure
system, usually a closed low or cutoff low, which is not tilted with
height, i.e., located similarly at all levels of the atmosphere. |
| VICINITY |
A proximity
qualifier used to indicate weather phenomena observed between 5 and
10 statute miles of the usual point of observation but not at the
station. |
| VIL |
Vertically-Integrated
Liquid water. A property computed by RADAP II and WSR-88D units
that takes into account the three-dimensional reflectivity of an echo.
The maximum VIL of a storm is useful in determining its potential
severity, especially in terms of maximum hail size. |
| VIRGA |
Precipitation
falling from the base of a cloud and evaporating before it reaches
the ground. |
| VIRTUAL
TEMPERATURE |
The temperature
a parcel of air would have if the moisture in it were removed and
its specific heat was added to the parcel. |
| VISIBILITY |
The horizontal
distance an observer can see and identify a prominent object. |
| VORT
MAX |
(Short
for vorticity maximum), a center, or maximum, in the vorticity field
of an airmass. |
| VORTICITY |
A measure
of the amount of "spin" (rotation) and "shear" in the atmosphere. |
| VORTEX |
An atmospheric
feature that tends to rotate. It has vorticity and usually has closed
streamlines. |
| W |
|
| WAA |
Warm
Air Advection |
| WALL
CLOUD |
An isolated
lowering of a cloud that is attached to the rain-free base of a thunderstorm,
generally to the rear of the visible precipitation area. Wall clouds
indicate the updraft of or the inflow to a thunderstorm. |
| WARM
FRONT |
A boundary
between a warm air mass that is replacing a cooler air mass. |
| WARNING |
Issued
when a particular hazard is "imminent" or already occurring (e.g.,
tornado warning, flash flood warning). |
| WATCH |
Forecast
issued in advance to alert the public of the possibility of a particular
hazard (e.g., tornado watch, flash flood watch). |
| WATER
EQUIVALENT |
The liquid
content of solid precipitation that has accumulated on the ground
(snow depth). The accumulation may consist of snow, ice formed by
freezing precipitation, freezing liquid precipitation, or ice formed
by the refreezing of melted snow. |
| WATER
VAPOR |
Water
substance in a gaseous state that comprises one of the most important
of all the constituents of the atmosphere. |
| WATERSPOUT |
A column
of rotating air over a body of water (i.e., a tornado over the water). |
| WAVE |
In meteorology
any pattern identifiable on a weather map that has a cyclic pattern,
or, a small cyclonic circulation in the early stages of development
that moves along a cold front. |
| WAVE
CREST |
The highest
point in a wave. |
| WAVE
TROUGH |
The lowest
point in a wave. |
| WAVELENGTH |
Physical
distance of one period (wave repeat). |
| WEATHER
BALLOON |
Large
balloon filled with helium or hydrogen that carries a radiosonde (weather
instrument) aloft to measure temperature pressure and humidity as
the balloon rises through the air. It is attached to a small parachute
so that when the balloon inevitably breaks, the radiosonde doesn't
hurtle back to earth dangerously quickly. |
| WEATHER
SYNOPSIS |
A description
of weather patterns affecting a large area. |
| WEDGE
(or WEDGE TORNADO) |
A large
tornado with a condensation funnel that is at least as wide (horizontally)
at the ground as it is tall (vertically) from the ground to cloud
base. |
| WFO |
Weather
Forecast Office. Oklahoma has 2 WFOs...one located in Tulsa and the
other in Norman. |
| WIND |
Air in
motion relative to the surface of the earth. |
| WIND
ADVISORY |
Issued
for sustained winds between 24 to 39 mph...or...sustained winds of
less than 25 miles per hour but frequent gusts between 25 and 39 miles
per hour. |
| WIND
ALOFT |
The wind
speeds and wind directions at various levels in the atmosphere above
the area of surface. |
| WIND
CHILL |
The additional
cooling effect resulting from wind blowing on bare skin. The wind
chill is based on the rate of heat loss from exposed skin caused by
the combined effects of wind and cold. The (equivalent) wind chill
temperature is the temperature the body "feels" for a certain combination
of wind and air temperature. |
| WIND
CHILL FACTOR |
The apparent
temperature which describes the cooling effect on exposed skin by
the combination of temperature and wind, expressed as the loss of
body heat. Increased wind speed will accelerate the loss of body heat.
The formula to calculate wind chill is: WC=.0817(3.71 V^.5 + 5.81
- .25 v)(T-91.4)+91.4 where V=wind speed in MPH and T=temperature
F. |
| WIND
CHILL ADVISORY |
Issued
when wind chill values of minus 20 degrees or colder are expected
which will cause exposed flesh to become quickly frostbitten or frozen. |
| WIND
CHILL WARNING |
Issued
when life-threatening wind chills of -50F or colder are expected. |
| WIND
DIRECTION |
The direction
from which the wind is blowing. |
| WIND
SHEAR |
The change
of wind speed or direction with distance or height. |
| WIND
SPEED |
The rate
at which air is moving horizontally past a given point. It may be
a 2-minute average speed (reported as wind speed) or an instantaneous
speed (reported as a peak wind speed, or gust). |
| WIND
VANE |
An instrument
that determines the direction from which a wind is blowing. |
| WINTER
STORM WATCH |
A significant
winter storm may affect your area, but its occurrence, location and
timing are still uncertain. A winter storm watch is issued to provide
12 to 36 hours notice of the possibility of severe winter weather.
A watch will often be issued when neither the path of a developing
winter storm nor the consequences of the weather event are as yet
well defined. Ideally, the winter storm watch will eventually be upgraded
to a warning when the nature and location of the developing weather
event becomes more apparent. A winter storm watch is intended to provide
enough lead time so those who need to set plans in motion can do so. |
| WINTER
STORM WARNING |
Issued
when when a variety of hazardous conditions are forecast to occur
across the area, or when there is difficulty in determining the type
of conditions which will predominate. A warning is used for winter
weather conditions posing a threat to life and property. |
| WINTER
WEATHER ADVISORY |
Issued
when one to 3 inches of new snow is expected or icing which makes
driving and walking hazardous. Tree branches and power lines may become
ice-coated but damage or breakage is not expected. An advisory can
also be issued when a variety of events are forecast to occur across
an area...or the type of event is difficult to specify.
An advisory for less than one inch may be issued if the time of
year or other circumstances warrant special caution in the opinion
of the forecaster. |
| WSR-88D |
Weather
Surveillance Radar - 1988 Doppler; NEXRAD
unit. |
| Z |
|
| ZONAL
FLOW (Zonal Wind) |
Large-scale
atmospheric flow in which the east-west component (i.e., latitudinal)
is dominant. |
| ZULU
TIME |
Same
as UTC, Universal Coordinated Time. Is is called Zulu because Z is
often appended to the time to distinguish it from local time. |
www.srh.weather.gov 
National Weather Service Forecast Office