TranspirationThe process by which water in plants is transferred into water vapor in the atmosphere. Evaporation of water through the leaves of plants.
Transport WindThe average wind over a specified period of time within a mixed layer near the surface of the earth.
Transportation sectorConsists of private and public passenger and freight transportation, as well as government transportation, including military operations.
Transverse BandsBands of clouds oriented perpendicular to the flow in which they are embedded. They often are seen best on satellite photographs.
Transverse RollsElongated low-level clouds, arranged in parallel bands and aligned parallel to the low-level winds but perpendicular to the mid-level flow.
TrapperA valley or basin in which cold air becomes trapped or pooled.
Travel TimeTime measured from the start of a dam breach to flooding at a particular location.
tree ringsa pattern observed in tree trunks, in which one band is usually equivalent to one year's growth.
Triple DopplerSince any wind has three components (say, in the x, y and z directions), and a single radar measures in only one direction (radial), a single radar cannot…
Triple PointThe intersection point between two boundaries (dry line, outflow boundary, cold front, etc.), often a focus for thunderstorm development.
Tropical AdvisoryOfficial information issued by tropical cyclone warning centers describing all tropical cyclone watches and warnings in effect along with details…
Tropical Analysis and Forecast BranchOne of three branches of the Tropical Prediction Center (TPC). It provides year-round products involving marine forecasting, aviation forecasts and…
Tropical CycloneA warm-core, non-frontal synoptic-scale cyclone, originating over tropical or subtropical waters with organized deep convection and a closed surface wind…
Tropical Cyclone Plan of the DayA coordinated mission plan that tasks operational weather reconnaissance requirements during the next 1100 to 1100 UTC day or as required, describes…
Tropical Cyclone Position EstimateThe National Hurricane Center issues a position estimate between scheduled advisories whenever the storm center is within 200 nautical miles of U.S.
Tropical Cyclone UpdateThis brief statement is issued by the National Hurricane Center in lieu of or preceding special advisories to inform of significant changes in a tropical…
Tropical DepressionA tropical cyclone in which the maximum 1-minute sustained surface wind is 33 knots (38 mph) or less.
Tropical DisturbanceA discrete tropical weather system of apparently organized convection--generally 100 to 300 mi in diameter--originating in the tropics or subtropics…
Tropical StormA tropical cyclone in which the maximum 1-minute sustained surface wind ranges from 34 to 63 knots (39 to 73 mph) inclusive.
Tropical Storm SummaryWritten by the Hydrometeorological Prediction Center* (HPC) after subtropical and names tropical cyclones have moved inland and advisories have been…
Tropical Storm WarningA warning for sustained surface winds, associated with a tropical cyclone, within the range of 34 to 63 knots (39 to 73 mph), expected in a specified…
Tropical Storm WatchAn announcement that a tropical storm poses or tropical storm conditions pose a threat to coastal areas generally within 36 hours.
Tropical Wave(formerly known as inverted trough) - A trough or cyclonic curvature maximum in the trade wind easterlies.
Tropical Weather DiscussionThese messages are issued 4 times daily by the Tropical Analysis and Forecast Branch (TAFB) to describe significant synoptic weather features in the…
Tropical Weather OutlookThis outlook normally covers the tropical and subtropical waters, discussing the weather conditions, emphasizing any disturbed and suspicious areas which…
Tropical Weather SummaryThe National Hurricane Center issues a monthly summary of tropical weather is included at the end of the month or as soon as feasible thereafter, to…
Tropical Western Pacific (TWP) site(TWP)The second ARM research site, it is located in the south Pacific Ocean occupying Manus Island, Nauru Island, and Darwin, Australia.
TropicsAreas of the Earth within 20° North and South of the equator.
TropopauseThe upper boundary of the troposphere, usually characterized by an abrupt change in lapse rate from positive (decreasing temperature with height) to…
Tropopause JetType of jet stream found near the tropopause. Examples of this type of jet are the subtropical and polar fronts.
TroposphereThe layer of the atmosphere closest to the Earth's surface.
TroughAn elongated area of relatively low atmospheric pressure, usually not associated with a closed circulation, and thus used to distinguish from a closed low.
TROWALTROugh of Warm Air ALoft. Typically used during winter weather, it is a "tongue" of relatively warm/moist air aloft that wraps around to the north and…
TsunamiOcean wave produced by earthquakes or underwater landslides.
Tsunami AdvisoryFor products of the Pacific Tsunami Warning Center (PTWC - Pacific (except Alaska, British Columbia and Western States) Hawaii, Caribbean (except Puerto…
Tsunami Information StatementA tsunami information statement is issued to inform emergency management officials and the public that an earthquake has occurred, or that a tsunami…
Tsunami WarningFor products of the Pacific Tsunami Warning Center (PTWC - Pacific (except Alaska, British Columbia and Western States) Hawaii, Caribbean (except Puerto…
Tsunami WatchFor products of the Pacific Tsunami Warning Center (PTWC - Pacific (except Alaska, British Columbia and Western States) Hawaii, Caribbean (except Puerto…
Tule FogRadiation fog in the Central Valley of California. It forms during night and morning hours in late fall and winter months following the first significant…
TurbidityThe relative clarity of water, which may be affected by material in suspension in the water.
TurbulenceIrregular motion of the atmosphere, as indicated by gusts and lulls in the wind.
Turkey TowerSlang for a narrow, individual cloud tower that develops and falls apart rapidly.
Turning PointA temporary point whose elevation is determined by additions and subtractions of backsights and foresights respectively.
TWEBTranscribed Weather Broadcasts - This NWS aviation product is similar to the Area Forecast (AF) except information is contained in a route format.
TwilightThe average time of civil twilight, which is the time between civil dawn and sunrise in the morning, and between sunset and civil dusk in the evening.
TwisterIn the United States, a colloquial term for a tornado.
Two-Ribbon FlareIn solar-terrestrial terms, a flare that has developed as a pair of bright strands (ribbons) on both sides of the main inversion ("neutral") line of the…
Type I, II, III, IV(In solar-terrestrial terms) -Emissions of the sun in radio wavelengths from centimeters to dekameters, under both quiet and disturbed conditions. Type I.
TyphoonA tropical cyclone in the Western Pacific Ocean in which the maximum 1-minute sustained surface wind is 64 knots (74 mph) or greater.
Typhoon SeasonThe part of the year having a relatively high incidence of tropical cyclones. In the western North Pacific, the typhoon season is from July 1 to December…
U BurstIn 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…
UCP(Unit Control Position): The WSR-88D radar operator uses this to control the entire radar system.
UGC(Universal Geographic Code) - (e.g. ANZ300 for Western Long Island Sound) are used in many National Weather Service text products to provide geographical…
UKMETA medium-range (3 to 7 day) numerical weather prediction model operated by the U nited K ingdom MET eorological Agency.
Ultraviolet IndexThis index provides important information to help you plan your outdoor activities in ways that prevent overexposure to the sun's rays.
ultraviolet radiation(UL-truh-VY-oh-let RAY-dee-AY-shun) Invisible rays that are part of the energy that comes from the sun.
Ultraviolet Radiation (UV)The energy range just beyond the violet end of the visible spectrum. Although ultraviolet radiation constitutes only about 5 percent of the total energy…
UmbraIn solar-terrestrial terms, the dark core or cores (umbrae) in a sunspot with penumbra, or a sunspot lacking penumbra.
UndercurrentA current below the upper currents or surface of a fluid body.
UnderflowThe movement of groundwater through the soil or a subsurface stratum, or under a structure; specifically, the water flowing beneath the bed of a stream…
UndersunAn 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…
UndertowA 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…
Unfinished oilsAll oils requiring further refinery processing, except those requiring only mechanical blending.
UnimodalA distribution having only one localized maximum, i.e., only one peak.
Unit Control PositionThe 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…
Unit HydrographThe direct runoff hydrograph resulting from a unit depth of excess rainfall produced by a storm of uniform intensity and specified duration.
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 information.
Universal Time (UT)By international agreement, the local time at the prime meridian, which passes through Greenwich, England.
Unmanned Aerospace Vehicle (UAV) Program(UAV)A U.S. Department of Energy program that uses an unmanned aerospace vehicle and occupied aircraft to make key climate measurements that cannot be made my…
Up-valley WindA diurnal thermally driven flow directed up a valley's axis, usually occurring during daytime; part of the along-valley wind system.
UpdraftA 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…
Upper air observationUpper air observation An observation made in the free atmosphere either directly or indirectly.
Upper atmosphereUpper atmosphere The general term applied to the atmosphere above the mesopause.
Upper LevelIn weather observing, the term applies to the portion of the atmosphere that is above the lower troposphere, generally 850 hPa and above.
Upper Level DisturbanceA disturbance in the upper atmospheric flow pattern which is usually associated with clouds and precipitation.
Upper Level SystemA general term for any large-scale or mesoscale disturbance capable of producing upward motion (lift) in the middle or upper parts of the atmosphere.