Subj : Weather Glossary (U)
To : All
From : Daryl Stout
Date : Mon Apr 22 2019 12:04 am
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.
***
U Burst
In solar-terrestrial terms, a fast radio burst spectrum of a flare. It
has a U-shaped appear- ance in an intensity-vs.-frequency plot
U.S. Geological Survey
(Abbrev. USGS)- The Federal Agency chartered in 1879 by congress to
classify public lands, and to examine the geologic structure, mineral
resources, and products of the national domain. As part of its mission,
the USGS provides information and data on the Nation's rivers and
streams that are useful for mitigation of hazards associated with floods
and droughts.
UCP
(Unit Control Position): The WSR-88D radar operator uses this to control
the entire radar system. One of the main things that the radar operator
will do at the UCP is change volume scan strategies of the antenna.
These volume scan strategies tell the radar how many elevation angles
will be used during a single volume scan (a volume scan is the
completion of a sequence of elevation angles), and the amount of time it
will take to complete that sequence of elevation cuts, each one being a
single rotation of the antenna's 1 degree beam at selected elevation
angles. The WSR-88D uses 3 scan strategies. They are the following:
14 elevation angles in 5 minutes (this is used during severe weather
situations), 9 elevation angles in 6 minutes (this is used when there is
precipitation within 248 nautical miles of the radar), and 5 elevation
angles in 10 minutes (this is used when there is no precipitation within
248 nautical miles). The radar operator at the UCP can also adjust the
radar products and help the users out with their communication problems.
UGC
(Universal Geographic Code) - (e.g. ANZ300 for Western Long Island Sound)
are used in many National Weather Service text products to provide
geographical information. This allows users easy automated processing and
redistribution of the information. More specifically, the purpose of the
UGC are to specify the affected geographic area of the event, typically
by state, county (or parish), or unique NWS zone (land and marine). The
only exception to the above is to define the weather synopsis part of
certain marine products.
UKMET
A medium-range (3 to 7 day) numerical weather prediction model operated
by the United Kingdom METeorological Agency. It has a resolution of 75
kilometers and covers the entire northern hemisphere. Forecasters use
this model along with the ECMWF and GFS in making their extended
forecasts (3 to 7 days).
ULJ
Upper Level Jet
Ultra High Frequency (UHF)
Those radio frequencies exceeding 300 MHz
Ultraviolet Index
This index provides important information to help you plan your outdoor
activities in ways that prevent overexposure to the sun's rays. It was
designed by the National Weather Service (NWS) and the Environmental
Protection Agency (EPA). Unlike some countries' indices, the United States
UV Index is not based upon surface observations. Rather, it is computed
using forecasted ozone levels, a computer model that relates ozone levels
to UV incidence on the ground, forecasted cloud amounts, and the
elevation of the forecast cities. The calculation starts with
measurements of current total ozone amounts for the entire globe,
obtained via two satellites operated by the National Oceanic and
Atmospheric Administration (NOAA). These data are then used to produce a
forecast of ozone levels for the next day at various points around the
country.
Category UV Index Time to Burn Actions to Take
Minimal 0 - 2 60 min. + Apply SPF sunscreen.
Low 3 - 4 45 min. Apply SPF sunscreen, wear a hat.
Moderate 5 - 6 30 min. Apply SPF 15, wear a hat.
High 7 - 9 15 - 24 min. Apply SPF 15 to 30, wear a hat and
sunglasses. Limit midday exposure.
Very High 10+ 10 min. Apply SPF 30; wear a hat, sunglasses,
and protective clothing; limit
midday exposure.
Ultraviolet Radiation
Electromagnetic radiation of shorter wavelength than visible radiation
but longer than x-rays.
Umbra
In solar-terrestrial terms, the dark core or cores (umbrae) in a sunspot
with penumbra, or a sunspot lacking penumbra.
Undercurrent
In hydrologic terms, a current below the upper currents or surface of a
fluid body.
Underflow
The lateral motion of water through the upper layers until it enters a
stream channel. This usually takes longer to reach stream channels than
runoff. This also called subsurface storm flow.
Undersun
An optical effect seen by an observer above a cloud deck when looking
toward the sun, as sunlight is reflected upwards off the faces of ice
crystals in the cloud deck. [Also known as subsun.]
Undertow
A relatively small-scale surf-zone current moving away from the beach.
Rip currents form as waves disperse along the beach causing water to
become trapped between the beach and a sandbar or other underwater
feature. The water converges into a narrow, river-like channel moving
away from the shore at high speed.
Unimodal
A distribution having only one localized maximum, i.e., only one peak.
Unit Control Position
The WSR-88D radar operator uses this to control the entire radar system.
One of the main things that the radar operator will do at the UCP is
change volume scan strategies of the antenna. These volume scan
strategies tell the radar how many elevation angles will be used during
a single volume scan (a volume scan is the completion of a sequence of
elevation angles), and the amount of time it will take to complete that
sequence of elevation cuts, each one being a single rotation of the
antenna's 1 degree beam at selected elevation angles. The WSR-88D uses
3 scan strategies. They are the following:
14 elevation angles in 5 minutes (this is used during severe weather
situations), 9 elevation angles in 6 minutes (this is used when there
is precipitation within 248 nautical miles of the radar), and 5
elevation angles in 10 minutes (this is used when there is no
precipitation within 248 nautical miles). The radar operator at the
UCP can also adjust the radar products and help the users out with
their communication problems.
Unit Hydrograph
The discharge hydrograph from one inch of surface runoff distributed
uniformly over the entire basin for a given time period.
Universal Geographic Code
(UGC) - UGC's, (e.g. ANZ300 for Western Long Island Sound) are used in
many National Weather Service text products to provide geographical i
nformation. This allows users easy automated processing and
redistribution of the information. More specifically, the purpose of
the UGC are to specify the affected geographic area of the event,
typically by state, county (or parish), or unique NWS zone (land and
marine). The only exception to the above is to define the weather
synopsis part of certain marine products.
Universal Time (UT)
By international agreement, the local time at the prime meridian,
which passes through Greenwich, England. Prior to 1972, this time was
called Greenwich Mean Time (GMT) but is now referred to as Coordinated
Universal Time or Universal Time Coordinated (UTC). It is a coordinated
time scale, maintained by the Bureau International des Poids et Mesures
(BIPM). It is also known a "Z time" or "Zulu Time".
More about UTC, and a table to convert UTC to your local time is posted
at:
http://www.srh.noaa.gov/jetstream/remote/radarfaq.htm#utc
UNSBL
Unseasonable
Unsettled
In solar-terrestrial terms, with regard to geomagnetic levels, a
descriptive word specifically meaning that 8 is less than or equal to
the Ap Index which is less than or equal to 15.
Unstable Air
Air that is able to rise easily, and has the potential to produce clouds,
rain, and thunderstorms.
UNSTBL
Unstable
Up-valley Wind
A diurnal thermally driven flow directed up a valley's axis, usually
occurring during daytime; part of the along-valley wind system.
Updraft
A small-scale current of rising air. If the air is sufficiently moist,
then the moisture condenses to become a cumulus cloud or an individual
tower of a towering cumulus or Cb.
Upper Level
In weather observing, the term applies to the portion of the atmosphere
that is above the lower troposphere, generally 850 hPa and above.
Upper Level Disturbance
A disturbance in the upper atmospheric flow pattern which is usually
associated with clouds and precipitation. This disturbance is
characterized by distinct cyclonic flow, a pocket of cold air, and
sometimes a jet streak. These features make the air aloft more unstable
and conducive to clouds and precipitation.
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. This term sometimes is used interchangeably with impulse
or shortwave.
Upper-air Weather Chart
Weather maps that are produced for the portion of the atmosphere above
the lower troposphere, generally at and above 850 mb. Isolines on these
maps usually represent the heights of a constant pressure surface, such
as the 500 mb surface.
UPR
Upper
Upslope Flow
Same as Orographic Lifting; 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.
Upslope Fog
A fog that forms when moist, stable air is carried up a mountain slope.
UPSLP
Upslope
Upstream
Towards the source of flow, or located in the area from which the flow
is coming.
Upstream Slope
The part of the dam which is in contact with the reservoir water. On
earthen dams, this slope must be protected from the erosive action of
waves by rock riprap or concrete.
UPSTRM
Upstream
Upwelling
In ocean dynamics, the upward motion of sub-surface water toward the
surface of the ocean. This is often a source of cold, nutrient-rich
water. Strong upwelling occurs along the equator where easterly winds
are present. Upwelling also can occur along coastlines, and is important
to fisheries and birds in California and Peru.
Urban and Small Stream Flood Advisory
This advisory alerts the public to flooding which is generally only an
inconvenience (not life-threatening) to those living in the affected
area. Issued when heavy rain will cause flooding of streets and
low-lying places in urban areas. Also used if small rural or urban
streams are expected to reach or exceed bankfull. Some damage to homes
or roads could occur.
Urban and Small Stream Flooding
Flooding of small streams, streets, and low-lying areas, such as
railroad underpasses and urban storm drains. This type of flooding is
mainly an inconvenience and is generally not life threatening nor is it
significantly damaging to property.
Urban Flash Flood Guidance
A specific type of flash flood guidance which estimates the average
amount of rain needed over an urban area during a specified period of
time to initiate flooding on small, ungaged streams in the urban area.
Urban Flooding
Flooding of streets, underpasses, low lying areas, or storm drains.
This type of flooding is mainly an inconvenience and is generally not
life threatening.
Urban Heat Island
The increased air temperatures in urban areas in contrast to cooler
surrounding rural areas.
UTC
By international agreement, the local time at the prime meridian, which
passes through Greenwich, England. Prior to 1972, this time was called
Greenwich Mean Time (GMT) but is now referred to as Coordinated
Universal Time or Universal Time Coordinated (UTC). It is a coordinated
time scale, maintained by the Bureau International des Poids et Mesures
(BIPM). It is also known a "Z time" or "Zulu Time".
More about UTC, and a table to convert UTC to your local time is posted
at:
http://www.srh.noaa.gov/jetstream/remote/radarfaq.htm#utc
UV Index
Ultraviolet Index
This index provides important information to help you plan your outdoor
activities in ways that prevent overexposure to the sun's rays. It was
designed by the National Weather Service (NWS) and the Environmental
Protection Agency (EPA). Unlike some countries' indices, the United States
UV Index is not based upon surface observations. Rather, it is computed
using forecasted ozone levels, a computer model that relates ozone levels
to UV incidence on the ground, forecasted cloud amounts, and the
elevation of the forecast cities. The calculation starts with
measurements of current total ozone amounts for the entire globe,
obtained via two satellites operated by the National Oceanic and
Atmospheric Administration (NOAA). These data are then used to produce a
forecast of ozone levels for the next day at various points around the
country.
Category UV Index Time to Burn Actions to Take
Minimal 0 - 2 60 min. + Apply SPF sunscreen.
Low 3 - 4 45 min. Apply SPF sunscreen, wear a hat.
Moderate 5 - 6 30 min. Apply SPF 15, wear a hat.
High 7 - 9 15 - 24 min. Apply SPF 15 to 30, wear a hat and
sunglasses. Limit midday exposure.
Very High 10+ 10 min. Apply SPF 30; wear a hat, sunglasses,
and protective clothing; limit
midday exposure.
UVM
Upward Vertical Motion (also known as Upward Vertical Velocity)
UVV
Upward Vertical Velocity (rising air)
UWNDS
Upper Winds
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