Only three ingredients are needed bythe atmosphere to spawn thunderstorms.

- Moisture- Instability- A lifting mechanismSounds pretty simple. Yeah, about as

simple as saying flying is a balance ofthrust versus drag, and lift versus gravity.

The atmosphere’s performance isanalogous to that of an aircraft. The per-formance of each aircraft has been thor-oughly researched on computers, studiedin wind tunnels, and tested in actualflight. The result is a performance enve-lope that helps the pilot predict perfor-mance as well the limits of safety. Toomuch weight and even maximum liftwon’t keep an aircraft aloft. Flap and slatsettings, along with power settings, willhelp the pilot establish a beautifulapproach.

Thunderstorms have a performanceenvelope which forecasters use on a dailyor even hourly basis. It’s a thermodynam-ic diagram or sounding chart called a

SkewT-Log P, or simply SkewT. Thesetools are available on the web. They dotake some training to use, but computersdo much of the analysis and produce sev-eral convective indices.

Much like a pilot studies the perfor-mance envelope of an aircraft to see whatcombination of settings influence the air-craft’s performance, forecasters studycomputer-generated SkewT diagrams tosee how the balance of moisture, instabil-ity, and wind shear, will influence thun-derstorm growth and strength.

At any temperature, the air can hold acertain amount of moisture or watervapor. The dew point represents theamount that is present. Condensation ofthis moisture occurs when the air temper-ature cools to the dew point. Warmer aircan hold more water vapor than cold air.

rontTheMay-JJune, 2002 Nat ional Weather Serv ice Cent ra l Region Vo lume 1 Number 3

Mission Statement

To enhance aviation safety byincreasing the pilots’ knowledgeof weather systems and processesand National Weather Serviceproducts and services.

Convective Indices - Gauges for measuringthe thunderstorm environment

Figure 1. Many properties of the atmosphere come together to initiate or to enhanceconvection. Forecasters look for the areas where these properties overlap or are at a max-imum. Here a cold front portion of a low pressure system acts as a forcing mechanism.

In this issue:

The three ingredients allthunderstorms need.

Three popular indices used byforecasters to predict the onset and strength of thunderstorms.

The Convective Outlook from the Storm Prediction Center, the key for locating potential thunderstorm development.

Gravity waves - the stealthyoffspring of thunderstormsthat produce turbulence.

An abridged glossary of acronyms used by the Storm Prediction Center and the Aviation Weather Center.

1

Moisture - The fuel for fireworks.

Cold FrontForcing

Mechanism

Mid level instabilityor short wave.

Moisture andLow level instability

Thunderstorm forecasting is a“what-if” game.

When water vapor changes to liquidwater, the latent heat stored in the watervapor is released. It is this latent heat thatplays such a significant role in thunder-storm development.

An invisible air parcel that is forcedto rise, cools independantly from the sur-rounding atmosphere at the dry lapse rateof about -3 degrees C per 1000 feet. Thisis a thermodynamic principle. It does thisin Orlando, Florida, Bessemer, Michigan,and Wichita Falls, Texas. The lapse rateof temperature in a layer of surroundingair will likely be, and usually is differentthan the dry rate. As a result, the parcel’stemperature usually will be different thanthe surrounding air, and the parcel may bestable or unstable as shown. See Figure 2.

A key player in convection is latentheat stored in water vapor. To create watervapor, evaporation must first occur. A panof water on the stove receives heat fromthe burner. This heat is stored in the watervapor as the water evaporates. This heatis not lost. It’s just “stored” for later use inthe water vapor molecules.

When water condenses back into vis-ible cloud droplets, the latent heat thatwas stored in the molecules during evap-oration is now released. This heat warmsthe independent air parcel, but it does notwarm the surrounding air by any mean-ingful amount. See Figure 3. The parcelnow cools at about -2 degrees C per 1000feet. As a result, the parcel is potentiallymore buoyant than the surrounding airthrough which it moves. The parcel con-tinues to rise until it reaches a level in theatmosphere where its temperaturebecomes the same or cooler than the sur-rounding air. Vertical motion stops at thatpoint.

Upward motion will stop when theparcel temperature becomes equal to orcooler than the surrounding air. Temper-ature inversions which are layers of airwhere temperature increases with heightdo this very well. The tropopause, around39,000 feet, is just such an inversion. Thelarge volume of the rising air spreads outat the tropopause, and forms a fibrousanvil.

Forecasters use SkewT diagrams todetermine the potential energy and buoy-

Figure 4. Plotting an air parcel’s ascent through the existing atmosphere is like usingthe performance chart for an aircraft. Forecasters determine the convective perfor-mance of the atmosphere and derive a number of convective indices. These indiceschange as temperature, wind, and humidity in the atmosphere change.

2

Figure 2. A rising parcel of air will become stable if it reaches a level in the atmos-phere where it becomes colder than the surrounding air. Likewise, the atmosphere isconsidered unstable if a rising parcel becomes warmer than the surrounding air.

Figure 3. When clouds form latent heat stored in the the water vapor is released andwarms the parcel. This makes it more buoyant than the air through which it moves.

ExistingDewpoint and Temperature

Cloud base

Tropopause

Moist lapserate

Air parcelbecomes

warmer than thesurrounding air.

The difference between theparcel temperature and theatmosphere at 500 millibars

is the Lifted Index

The area between thetemperature of the airand that of the parcelfrom the cloud base tonear the tropopause isConvective Available

Potential Energy,CAPE

Stable air or Unstable air? That is the question.

Latent heat released dur-ing condensation warmsthe parcel and makes itmore buoyant.

The Convective Outlookholds the buzz words for convection.

or upper level disturbance bringing apocket of cooler air into the region.

The other way is to make the temper-ature of the rising parcel warmer than thesurrounding air. Condensing more watervapor from the parcel will add more heatand buoyancy for the parcel. Higher dewpoints represent that increased availablewater vapor. Forecasters look for highdewpoints on hourly surface charts andMETAR reports because this is the gaso-line thunderstorms guzzle as they preparefor battle with air traffic system. Termslike moisture plume or surface dew points

are used by SPC to focus on this energysource. Injecting more moisture into apotential thunderstorm environmentwould cause the dashed path of the risingparcel in Figure 4 to move to the right andproduce more CAPE.

CAPE can be calculated from anylevel. Surface based CAPE or SBCAPEuses hourly METAR temperatures, butcan over estimate conditions. MixedLayer CAPE or MLCAPE uses condi-tions in a shallow layer above the surface.MUCAPE or Most Unstable CAPE is atype that represents the worst case sce-

ancy of air parcels and their possible evo-lution into thunderstorms. A number ofindices derived from the SkewT are eval-uated by forecasters at the SPC and arediscussed in their Convective Outlook.See Figure 5. Three of the most popularindices for the pre-ignition stage of thun-derstorms are LI, CAPE, and CIN.

Figure 4 is an example of how stormdevelopment is studied using a SkewT.

An air parcel is assumed to be liftedby one of the forcing mechanisms such asstrong heating, a cold front, or upper leveldisturbance. The air parcel obeys the lawsof thermodynamcs and cools as it risesand expands. At 500 millibars, or about18,000 feet the calculated parcel tempera-ture is compared with that of the sur-rounding air. The difference betweenthese two temperatures is the LI and is ameasure of the buoyancy of an air parcel.A negative number implies that the sur-rounding air is cooler than the lifted par-cel. In other words, the parcel would bewarmer and more buoyant compared thethe surrounding air.

LI was developed years ago and isstill a very reliable index of instability.LIs are calculated hourly. They can becalculated using surface METAR reportsand the 500 millibar temperature forecast-ed by the atmospheric models. Or LIs canbe calculated using another level of theatmosphere as the starting point. Thechoice rests with the forecaster.

CAPE, is related to LI, but is a morecomplete measure of the atmosphere’senergy. CAPE reflects the strength of athunderstorm updraft, and depicts theenergy in the atmosphere from the pointwhere clouds form and will be uninhibit-ed by any inversion, up to the tropopause.The units for CAPE are Joules per kilo-gram or sometimes just mentioned asJoules in discussions from the StormPrediction Center. CAPE is depicted bythe red shaded area on the SkewT inFigure 4.

Area on a SkewT is equivalent toenergy. The red shaded area representingconvective energy in the atmosphere canbe expanded in two ways. One is to coolthe air aloft so that the red temperatureline on the chart is displaced to the left.This can be done by a short wave trough

3

STORM PREDICTION CENTER...NWS/NCEP...NORMAN OK DAY 1 CONVECTIVE OUTLOOK...REF AWIPS GRAPHIC PGWE46 KWNS.

VALID 111300Z - 121200Z

THERE IS A SLGT RISK OF SVR TSTMS TO THE RIGHT OF A LINE FROM DUA 50 SSW ADM30 S SPS 50 SE CDS CDS 25 NNW GAG 40 NNW P28 SLN 35 NNE MHK 35 N STJ 35 NEMKC JLN MKO DUA.

GEN TSTMS ARE FCST TO THE RIGHT OF A LINE FROM 35 WSW ERI CAK ZZV LOZ CSVCHA RMG LGC CSG ABY MGR VLD 30 ENE GNV ORL AGR 60 S FMY...CONT... 40 ESE 7R4HEZ GLH MEM EVV 45 SSW HUF MTO 45 NNW SLO BLV 55 N HOT 45 N TYR 30 NNE ACTBWD 50 NE BGS 25 WNW CDS 50 NE AMA 25 NNE CAO TAD 25 WNW PUB FCL CYS 40SSW BFF SNY 35 SW IML 40 SW MCK 40 N HLC EAR BUB ANW PHP Y22 40 ENE DIK 65WSW DVL JMS 45 NE ATY 40 NE RWF 40 NNW IWD.

--- SYNOPSIS ---PROGRESSIVE UPPER AIR PATTERN FORECAST TO CONTINUE ACROSS CONUS. PRIMA-RY PERTURBATION WILL BE SHORTWAVE TROUGH NOW EVIDENT ON MOISTURE CHAN-NEL IMAGERY FROM NM NWD TO ERN MT...AND FORECAST TO DEAMPLIFY SLIGHTLY ONSRN END AS IT MOVES EWD ACROSS GREAT PLAINS TODAY. AT SURFACE...WAVYFRONT -- NOW ANALYZED FROM WRN WI SWWD ACROSS ERN NEB TO NEAR CO/OKBORDER -- IS FORECAST TO MOVE SLOWLY SWD ACROSS TX/OK PANHANDLES TODAYAND EWD OVER CENTRAL PLAINS/LOWER MO VALLEY. MEANWHILE...VERTICAL MIXINGSHOULD SHIFT DRYLINE EWD ACROSS PANHANDLES TO NEAR 100W LONGITUDE...WITHTRIPLE POINT SOMEPLACE OVER NWRN OR FAR W-CENTRAL OK BY 00Z.

--- SRN PLAINS ---WIDELY SCATTERED TO SCATTERED TSTMS POSSIBLE INVOF AND NE OF TRIPLE POINTBY 00Z...COVERAGE ISOLATED TO WIDELY SCATTERED FARTHER S ALONG/E OF DRY-LINE. WITH PERSISTENT WLY MID LEVEL FLOW OVER REGION AND SEVERAL DAYS OFHEATING ALREADY GENERATING ELEVATED/MIXED LAYER...CAPPING IS A CONCERN SOF TRIPLE POINT. HOWEVER...PRIND WEAK COOLING IN CAP LAYER...INCREASING DIABATIC HEATING AS W EDGE OF CIRROFORM CLOUD SHIELD PASSESEWD...AND CONVERGENCE/LIFT ALONG FRONT AND DRYLINE SHOULD BE SUFFICIENTFOR RISK OF TSTMS. GIVENPROGGED FAVORABLE VERTICAL SHEAR PROFILES...SEVERAL SUPERCELLS WITHLARGE HAIL AND SEVERE DOWNDRAFTS ARE FORECAST.

STEEP LAPSE RATES SHOULD BE MAINTAINED BY MERIDIONAL PLUME OF LARGESCALE DPVA/ASCENT IN 18-00Z TIME FRAME -- AHEAD OF TROUGH LEAVING ROCKIES --COMBINING WITH PRIMARILY MID-UPPER 50S SURFACE DEW POINTS TO YIELD SBCAPEAPPROXIMATELY 2000 J/KG. VERTICAL SHEAR WILL BE FAVORABLE WITH 150-250 J/KGSRH...40-50 KT 0-6 KM VECTOR SHEAR...AND SR FLOWS GENERALLY AOA 15 KTTHROUGHOUT TROPOSPHERE. HOWEVER...RELATIVELY HIGH CLOUD BASES EXPECTEDINITIALLY FOR CELLS FROM TRIPLE POINT REGION SWD INVOF DRYLINE...GIVEN FORE-CAST SURFACEDEW POINT DEPRESSIONS...CONTRIBUTING TO POTENTIAL FOR COLD STORM OUT-FLOWS AND LOW TORNADO PROBABILITIES. TORNADO POTENTIAL MAY BE ENHANCEDFOR ANY DISCRETE CELLS REMAINING 2-3 HOURS AFTER INITIAL DEVELOPMENT WHICHMOVE EWD INTO COOLER AND MORE MOISTURE-RICH LOW LEVEL AIR MASS...ESPE-CIALLY INVOF BOUNDARIES.

Figure 5. Convective outlooks from the Storm Prediction Center are the emergingmethod used by the Aviation Weather Center as the outlook for Convective SIGMETs.This ACUS01 KWNS product mentions the indices that forecasters are monitoring.

The Lifted Index - Ole reliable

CAPEThe total package

nario. SPC forecasters select the appropri-ate type of CAPE for the day.

In a general sense, values of LiftedIndex and CAPE have been associatedwith the severity of thunderstorms. Thosegeneral rankings are shown in Figure 6. Itshould be noted that these CAPE valuescannot be applied the same throughout thecountry. They are most applicable to thecentral U.S. Low values of CAPE whichwould not lead to violent thunderstormsin the midwest may produce strong thun-derstorms along the west coast or in high-er terrain.

Cap Strength is an inhibiting factorfor thunderstorms. Some days the atmos-phere is hot and muggy and just seemsright for massive storms, but nothing hap-pens. This may be due to a temperatureinversion between 2000 and 5000 feetabove ground level caused by warm airbeing brought into the area by the wind.The process is called warm air advection.Any air parcel rising into this inversionwould become cooler than the surround-ing layer of warm air and would sink orcease to rise. The cap can be expressed indegrees C or in negative Joules per kilo-gram of energy.

In Figure 7, an inversion is present.As the air parcel rises, it enters the warmlayer and is now cooler than the sur-rounding air. The air parcel sinks.Convection caused by surface heatingnow ceases.

Convective Outlooks and MesoscaleConvective Discussions from the SPCmay reference a cap when forecasting theonset of convection. Terms such as‘strong cap” or “a weakening cap” mayalso be used. A cap can be expressed as atemperature or as negative Joules per

4

Figure 6. Thunderstorms develop as a result of the temperature structure or instabili-ty aloft. A number of indices, derived from that structure, are used by forecasters todetermine the growth potential and severity of thunderstorms.

Figure 8. The Storm Prediction center has a number of links to hourly maps of themost often used indices. The Experimental Techniques page, specifically the experi-mental Mesoanalysis Graphics option links to a page with which you can monitorhourly trends in CAPE, Cap Strength and Lifted Index. The direct link is:www.spc.noaa.gov/exper/mesoanalysis/

Lifted Index* > +2 Convective activity unlikely.* 0 to +2 Stable, but weak convection

possible if a strong lifting or forcing mechanism is present.

* 0 to -3 Marginally unstable, thunder-storms probable.

* -4 to -6 Moderately unstable.Severe thunderstorms possible.

* -7 to -9 Very unstable. severe thunderstorms probable.

* < -9 Extremely unstable. severe thunderstorms likely.

CAPE* <1000 generally weak convection* 1000 - 2000 Showers probable,

isolated thunderstorms possible.* 2000 - 3000 Thunderstorms probable* >3000 Severe thunderstorms probable,

tornadoes possible.

Cap Strength* >= 2 Convection suppressed* < 2 Convection uninhibited

The cap may also be expressed innegative Joules perkilogram.The more negative the value, thestronger the cap that must be over-come. A negative cap value of -200Joules per kilogram or more isconsidered a strong cap.

The ExperimentalTechniques optionleads to this page.

Then click on themap here to go to a regional-ized map showingvarious convectiveindices.

The Cap Putting a lid on convection

Figure 7. The Cap is a warm tempera-ture inversion layer. A parcel rising intothis inversion will be cooler than the sur-rounding air and will sink.

Caplayer

Inversion

kilogram of energy needed to overcomeit.

Figure 2 showed how the tempera-ture structure of the atmosphere, or lapserate determines whether an air parcel isgoing to be stable or unstable relative toits surroundings. The rate at which theatmosphere cools with altitude is calledthe lapse rate. The SPC often mentionslapse rates in Convective Outlooks andMesoscale Convective Discussions.

The term steep lapse rate indicatesthat temperature of the air decreasesrapidly with height A parcel risingthrough a layer with a steep lapse ratewould see the temperature of the sur-rounding air become rapidly cooler as theparcel rises. So the parcel would be muchwarmer and more buoyant.

As stated earlier, warm air advectionin the lower layers of the atmosphere cancreate an inversion or cap aloft which ini-hibits surface based convection.However, just above that inversion steeplapse rates develop which are favorablefor convection.

Forecasters may mention elevatedconvection in these situations. Thatmeans that strong or severe thunder-storms are possible if a forcing mecha-nism like a front or upper level distur-bance moves through the region to lift theair to that elevated region that is unstable.So when the the atmosphere indicateshigh CAPE values, but is capped, strongconvection is still possible if a forcingmechanism moves through.

Maps of computed indices are avail-able every hour on the web. The SPCpage tracks hourly values of Lifted Index,CAPE, amd cap strength, or ConvectiveINhibition (CIN). See Figure 8. The pageis available at:

The map zooms in on the portion ofthe country that is facing the greatestsevere convective potential. Your particu-lar part of the country may not be shown.

NOAA’s UCAR RAP page shown inFigure 9 provides full national coverageof convective indices. That page is avail-able at:

The Rapid Update Cycle, RUC,5

Figure 9. The SPC page links to the NOAA University Corporation for AtmosphericResearch (UCAR), and the Realtime Analysis and Prediction (RAP) pages. Forecastsfor CAPE, CIN, and Lifted Index are available at frequent intervals. For near termforecasts, out to 12 hours, use the RUC model. For longer term forecasts from 12 to 48hours, the ETA model is a good choice.

Figure 10. Tracking CAPE and CIN hourly draws attention to potential thunderstormdevelopment. It is these values, plus LI, that forecasters use often. CIN is important tomonitor because the atmosphere may be unstable aloft, but low level stability inferredby CIN may delay or even prevent convection.

Current and ForecastConvective Indices

Convective Inhibition, or CIN isindicated by blue-outlined clearor hatched areas. The more nega-tive numbers imply capping.

Convective Available Potential Energy, or CAPEis a good indicator of buoyant energy of an airparcel which would strengthen the thunderstormupdraft.

Lapse rates

Let me draw you a picture

www.rap.ucar.edu/weather/model/

www.spc.noaa.gov/exper/mesoanalysis/

model is good for near term, hourly track-ing of convective indices. The RUC is runevery hour using forecast model data butalso uses hourly METAR reports to sup-ply updates on surface conditions fromwhich convection might start.

Another model choice on the UCARRAP page is the ETA. This is an accurateatmospheric model widely used by fore-casters.

The RAP page allows the pilot tobuild a set of forecast maps. Select thedesired parameters, such as CAPE anddew point, and the number of hours in thefuture. Those hours are the valid timesafter the run time of the model. The ETAis run every 6 hours. So be sure to checkthe valid times in the map header to makesure when the forecast is valid.

Other valuable data for pilots isavailable on the UCAR RAP page inFigure 9. Color maps of temperatures andwinds aloft are a click away using the listof options under the “Aloft Plots” header.

Even though the elite StormPrediction Center is on top of the dailyconvection, it’s nice to have maps depict-ing the most-used convective indices sopilots and dispatchers can keep tabs ondeveloping danger spots. Tie these in withAWC’s Collaborative ConvectiveForecast Product and SPC’s ConvectiveOutlook, and Mesoscale Discussions, andyou’ll be adequately equipped for whatlies ahead.

Besides the immediate and obviousthreat that thunderstorms pose, their rapiddevelopment can produce other unexpect-ed hazards.

The following article is from WarrenL Qualley, Manager of Weather Servicesat American Airlines. The opinions andsuggestions reflect operating practices atAmerican Airlines. Your company oragency policies may be different.

Turbulence andThunderstorm Season!

Warren L. QualleyManager Weather Services

American AirlinesMost of us assume that turbulence is

a wintertime phenomenon. And in thecase of true clear air turbulence, or thatcaused by mountain waves, that's a prettyaccurate statement. However, turbulencecan and does occur every month of the

year. In reviewing several years worth ofturbulence reporting records in the com-mercial aviation industry, it turns out thatthe greatest number of incidents occur inApril, followed by December, January,March and October.

Why April, March and October? Tworeasons: first, the real clear air turbulenceseason is just ending (March and April) orjust beginning (October) and, second, themain part of thunderstorm season getsinto full swing in March (southern U.S.and Caribbean) and April, and is just end-ing in October.

The next question you might ask is"what do thunderstorms and clear air tur-bulence have to do with one another?".The answer to that is the bumpy air due towhat we will call Convective-InducedTurbulence or CIT. Now every pilotknows that one of the by-products ofthunderstorms is turbulence of varyingintensities. But thunderstorms also pro-duce gravity waves that spread outward,upward and downward from the thunder-storm cloud itself. There have beenreports of turbulence encounters as highas 15,000 feet in the clear air above thun-derstorm clouds and horizontally as faraway as 100 miles from the storm. Thisturbulence can be amplified if it occursnear the tropopause level, since the troptraps the gravity wave as it spreads out-ward from the thunderstorm.

Before pilots start avoiding individ-ual thunderstorms by the distancesdescribed above, they should know thatturbulence doesn't occur in the same wayor the same distance away from eachthunderstorm. And unfortunately, there'sno operational tool currently availablethat tactically measures and predicts anytype of turbulence, including CIT.

Pilots should be particularly aware oftheir environment relative to thunder-storms by actively and aggressively usingtheir on-board radar. Some of the moreserious CIT encounters have occurredwhen a flight is in the clear on top of a cir-rus cloud and a developing thunderstormpunches up from underneath. The experi-ence in not unlike hitting a speed bump ona road while traveling at 60 mph.

Suffice it to say that when in a thun-derstorm environment, even when not inclouds, there may be light to moderate, oreven greater, turbulence due to Convec-tive Induced Turbulence.

- A visit to the FAA nerve center in Herndon Virginia.

- A message from Jack May, Directorof the Aviation Weather Center.

- Terminal Aerodrome Forecast (TAF) verification program of the National Weather Service.

The editors welcome comments and-concerns from our readers, and we willrespond to any question or comment.Some responses may be delayed in orderto ensure that the content of that responseis consistent with government policy.Thank you.

We are pleased to announce the addi-tion of our new associate editor, JimRoets, Forecaster at the Aviation WeatherCenter. Jim brings a wealth of experience,talent and initiative, and qaulity focus.

Send comments and suggestions to:craig.sanders@noaa.govsally.pavlow@noaa.govjames.roets@noaa.gov

The Front is published bimonthly andis available on the NWS Central Regionaviation page at:www.crh.noaa.gov/crh/aviation/thefront.html

6

Figure 11. Gravity waves develop as aresult of strong convection. The result ismuch like releasing an air bubble fromthe bottom of a calm container of water.The gravity waves produce turbulence,and they can sometimes be seen well onsatellite imagery. They can even producenew convection where they intersectother existing boundaries. This gravitywave was documented by Roger Edwardsof the Storm Prediction Center.

Coming up next time...

Appendix

Contractions used by the NWS and itsnational prediction centers.

The list contains most of the contractionsused operationally in SPC’s ConvectiveOutlooks, Mesoscale Discussions, and byAWC’s AIRMETs, SIGMETs, ConvectiveSIGMETs, and Area Forecasts.

Contractions most commonly usedby NWS national prediction centers

- A -

ABNDT AbundantABNML AbnormalABT AboutABV AboveAC Convective OutlookACCAS Altocumulus

CastellanusACCUM AccumulateACFT AircraftACLT AccelerateACLTD AcceleratedACLTG AcceleratingACLTS AcceleratesACPY AccompanyACRS AcrossACSL Altocumulus Standing

LenticularusACTV ActiveACTVTY ActivityACYC AnticycloneADJ AdjacentADL AdditionalADQT AdequateADQTLY AdequatelyADRNDCK AdirondackADVCT AdvectADVCTD AdvectedADVCTG AdvectingADVCTN AdvectionADVCTS AdvectsADVN AdvanceADVNG AdvancingADVY AdvisoryADVYS AdvisoriesAFCT AffectAFCTD AffectedAFCTG AffectingAFDK After dark

AFT AfterAFTN AfternoonAGL Above ground levelAGN AgainAGRD AgreedAGRS AgreesAGRMT AgreementAHD AheadAK AlaskaAL AlabamaALF AloftALG AlongALGHNY AlleghenyALQDS All quadrantsALSTG Altimeter settingALTA AlbertaALTHO AlthoughALTM AltimeterALUTN AleutianAMD AmendAMDD AmendedAMDG AmendingAMDT AmendmentAMP AmplifyAMPG AmplifyingAMPLTD AmplitudeAMS Air massAMT AmountANLYS AnalysisANS AnswerAOA At or aboveAOB At or belowAP Anomolous

PropagationAPCH ApproachAPCHG ApproachingAPCHS ApproachesAPLCN AppalachianAPLCNS AppalachiansAPPR AppearAPPRG AppearingAPPRS AppearsAPRNT ApparentAPRNTLY ApparentlyAPRX Approximate

APRXLY ApproximatelyAR ArkansasARND AroundARPT AirportASAP As soon as possibleASL Above Sea LevelASMD As amendedASOS Automated Surface

Observing SystemASSOCD AssociatedASSOCN AssociationATLC AtlanticATTM At this timeATTN AttentionAVBL AvailableAVG AverageAVN Aviation ModelAWIPS Advanced Interactive

Weather ProcessingSystem

AWOS Automated Weather Observing System

AWT AwaitingAZ ArizonaAZM Azimuth

- B -

BACLIN BaroclinicBAJA Baja CaliforniaBATROP BarotropicBC Patches (METAR code)BC British ColumbiaBCH BeachBCKG BackingBCM BecomeBCMG BecomingBCMS BecomesBD Blowing dustBDA BermudaBDRY BoundaryBFDK Before darkBFR BeforeBGN Begin

BGNG BeginningBGNS BeginsBHND BehindBINOVC Breaks in overcastBKN BrokenBL Blowing (METAR code)BLD BuildBLDG BuildingBLDS BuildsBLDUP BuildupBLKHLS Black HillsBLKT BlanketBLKTG BlanketingBLKTS BlanketsBLO BelowBLZD BlizzardBN Blowing sandBND BoundBNDRY BoundaryBNDRYS BoundariesBNTH BeneathBOOTHEEL BootheelBR Mist (>= 5/8 SM)

(METAR code)BR BranchBRG BranchingBRS BranchesBRF BriefBRK BreakBRKG BreakingBRKHIC Breaks in higher cloudsBRKS BreaksBRKSHR BerkshireBRKSHRS BerkshiresBRM BarometerBS Blowing snowBTWN BetweenBYD Beyond

- C -

C CelsiusCA CaliforniaCAA Cold Air Advection

CARIB CaribbeanCASCDS CascadesCAVOK Ceiling and visibility OKCAVU Ceiling and visibility

unlimitedCB CumulonimbusCBS CumulonimbiCC CirrocumulusCCLDS Clear of cloudsCCLKWS Counter-clockwiseCCSL Standing lenticular

cirrocumulusCDFNT Cold frontCDFNTL Cold frontalCFP Cold front passageCG Cloud-to-groundCHC ChanceCHCS ChancesCHG ChangeCHG ChangedCHGG ChangingCHGS ChangesCHSPK ChesepeakeCI CirrusCIG CeilingCIGS CeilingsCLD CloudCLDNS CloudinessCLDS CloudsCLKWS ClockwiseCLR ClearCLRG ClearingCLRS ClearsCMPLX ComplexCNCL CancelCNCLD CancelledCNCLG CancellingCNCLS CancelsCNDN CanadianCNTR CenterCNTRD CenteredCNTRLN CenterlineCNTRS CentersCNTRL CentralCNTY County

CNTYS CountiesCNVG ConvergeCNVGG ConvergingCNVGNC ConvergenceCNVTN ConvectionCNVTV ConvectiveCNVTVLY ConvectivelyCNFDC ConfidenceCO ColoradoCOMPAR CompareCOMPARG ComparingCOMPARD ComparedCOMPARS ComparesCOND ConditionsCONT ContinueCONTD ContinuedCONTLY ContinuallyCONTG ContinuingCONTRAILS Condensation TrailsCONTS ContinuesCONTDVD Continental DivideCONUS Continental U.S.COORD CoordinateCOR CorrectionCPBL CapableCPC Climate Prediction

CenterCRC CircleCRCLC CirculateCRCLN CirculationCRNR CornerCRNRS CornersCRS CourseCS CirrostratusCSDR ConsiderCSDRBL ConsiderableCST CoastCSTL CoastalCT ConnecticutCTGY CategoryCTSKLS CatskillsCU CumulusCUFRA Cumulus FractusCVR CoverCVRD Covered

CVRG CoveringCVRS CoversCYC CyclonicCYCLGN Cyclogenesis

- D -

DABRK DaybreakDALGT Day lightDBL DoubleDC District of ColumbiaDCR DecreaseDCRD DecreasedDCRG DecreasingDCRGLY DecreasinglyDCRS DecreasesDE DelawareDEG DegreeDEGS DegreesDELMARVA Delaware-Maryland-

VirginiaDFCLT DifficultDFCLTY DifficultyDFNT DefiniteDFNTLY DefinitelyDFRS DiffersDFUS DiffuseDGNL DiagonalDGNLLY DiagonallyDIGG DiggingDIR DirectionDISC DiscontinueDISCD DiscontinuedDISCG DiscontinuingDISRE DisregardDISRED DisregardedDISREG DisregardingDKTS DakotasDLA DelayDLAD DelayedDLT DeleteDLTD DeletedDLTG DeletingDLY Daily

DMG DamageDMGD DamagedDMGG DamagingDMNT DominantDMSH DiminishDMSHD DiminishedDMSHG DiminishingDMSHS DiminishesDNDFTS DowndraftsDNS DenseDNSLP DownslopeDNSTRM DownstreamDNWND Down windDP DeepDPND DeepenedDPNS DeepensDPR DeeperDPNG DeepeningDPTH DepthDR Drifting (METAR code)DRFT DriftDRFTD DriftedDRFTG DriftingDRFTS DriftsDRZL DrizzleDS Duststorm

(METAR code)DSCNT DescentDSIPT DissipateDSIPTD DissipatedDSIPTG DissipatingDSIPTN DissipationDSIPTS DissipatesDSND DescendDSNDG DescendingDSNDS DescendsDSNT DistantDSTBLZ DestabilizeDSTBLZD DestabilizedDSTBLZG DestablizingDSTBLZS DestablizesDSTBLZN DestablizationDSTC DistanceDTRT DeteriorateDTRTD Deteriorated

DTRTG DeterioratingDTRTS DeterioratesDU Widespread dust

(METAR code)DURG DuringDURN DurationDVLP DevelopDVLPD DevelopedDVLPG DevelopingDVLPMT DevelopmentDVLPS DevelopsDVRG DivergeDVRGG DivergingDVRGNC DivergenceDVRGS DivergesDVV Downward vertical

velocityDWNDFTS DowndraftsDWPNT DewpointDWPNTS DewpointsDX DuplexDZ Drizzle (METAR code)

- E -

E EastEBND East boundEFCT EffectELNGT ElongateELNGTD ElongatedELSW ElsewhereEMBDD EmbeddedEMERG EmergencyENCTR EncounterENDG EndingENE East-northeastENELY East-northeasterlyENERN East-northeasternENEWD East-northeastwardENHNC EnhanceENHNCD EnhancedENHNCG EnhancingENHNCS EnhancesENHNCMNT Enhancement

ENTR EntireERN EasternERY EarlyERYR EarlierESE East-southeastESELY East-southeasterlyESERN East-southeasternESEWD East-southeastwardESNTL EssentialESTAB EstablishESTS EstimatesETA Eta modelETC Et ceteraETIM Elapsed timeEVE EveningEWD EastwardEXCLV ExclusiveEXCLVLY ExclusivelyEXCP ExceptEXPC ExpectEXPCD ExpectedEXPCG ExpectingEXTD ExtendEXTDD ExtendedEXTDG ExtendingEXTDS ExtendsEXTN ExtensionEXTRAP ExtrapolateEXTRAPD ExtrapolatedEXTRM ExtremeEXTRMLY ExtremelyEXTSV Extensive

- F -

F FarenheitFA Aviation area forecastFAH FarenheitFAM FamiliarFC Funnel cloud

(METAR code)+FC Tornado/waterspout

(METAR code)FCST Forecast

FCSTD ForecastedFCSTG ForecastingFCSTR ForecasterFCSTS ForecastsFG Fog (< 5/8SM)

(METAR code)FIG FigureFILG FillingFIRAV First availableFL FloridaFLG FallingFLRY FlurryFLRYS FlurriesFLT FlightFLW FollowFLWG FollowingFM FromFMT FormatFNCTN FunctionFNT FrontFNTL FrontalFNTS FrontsFNTGNS FrontogenesisFNTLYS FrontolysisFORNN ForenoonFPM Feet per minuteFQT FrequentFQTLY FrequentlyFRM FormFRMG FormingFRMN FormationFROPA Frontal passageFROSFC Frontal surfaceFRST FrostFRWF Forecast wind factorFRZ FreezeFRZN FrozenFRZG FreezingFT FeetFT Terminal forecastFTHR FurtherFU Smoke (METAR code)FVRBL FavorableFWD ForwardFYI For your information

FZ Freezing (METAR code)

- G -

G GustGA GeorgiaGEN GeneralGENLY GenerallyGEO GeographicGEOREF Geographical referenceGF Ground fogGICG Glaze icingGLFALSK Gulf of AlaskaGLFCAL Gulf of CaliforniaGLFMEX Gulf of MexicoGLFSTLAWR Gulf of St. LawrenceGND GroundGNDFG Ground fogGOES Geostationary Opera-

tional Evnironmental Satellite

GR Hail (METAR code)GRAD GradientGRDL GradualGRDLY GraduallyGRT GreatGRTLY GreatlyGRTR GreaterGRTST GreatestGRTLKS Great LakesGS Small hail/snow pellets

(METAR code)GSTS GustsGSTY GustyGV Ground visibility

- H -

HAZ HazardHCVIS High clouds visibleHDFRZ Hard freezeHDSVLY Hudson ValleyHDWND Head wind

HGT HeightHI HighHIER HigherHIFOR High level forecastHLF HalfHLTP HilltopHLSTO HailstonesHLYR Haze layer aloftHND HundredHPC Hydrometeorological

Prediction CenterHR HourHRS HoursHRZN HorizonHTG HeatingHURCN HurricaneHUREP Hurricane reportHV HaveHVY HeavyHVYR HeavierHVYST HeaviestHWVR HoweverHWY HighwayHZ Haze (METAR code)

- I -

IA IowaIC Ice crystals

(METAR code)IC IceICG IcingICGIC Icing in cloudsICGIP Icing in precipitationID IdahoIL IllinoisIMDT ImmediateIMDTLY ImmediatelyIMPL ImpulseIMPLS ImpulsesIMPT ImportantINCL IncludeINCLD IncludedINCLG Including

INCLS IncludesINCR IncreaseINCRD IncreasedINCRG IncreasingINCRGLY IncreasinglyINCRS IncreasesINDC IndicateINDCD IndicatedINDCG IndicatingINDCS IndicatesINDEF IndefiniteINFO InformationINLD InlandINSTBY InstabilityINTCNTL IntercontinentalINTL InternationalINTMD IntermediateINTMT IntermittentINTMTLY IntermittentlyINTR InteriorINTRMTRGN Intermountain regionINTS IntenseINTSFCN IntensificationINTSFY IntensifyINTSFYD IntensifiedINTSFY IntensifyingINTSFYS IntensifiesINTSTY IntensityINTVL IntervalINVRN InversionIOVC In overcastINVOF In vicinity ofIP Ice pelletsIPV ImproveIPVG ImprovingIR InfraredISOL IsolateISOLD Isolated

- J -

JCTN JunctionJTSTR Jet stream

- K -

KFRST Killing frostKLYR Smoke layer aloftKOCTY Smoke over cityKS KansasKT KnotsKY Kentucky

- L -

LA LouisianaLABRDR LabradorLAPS Local Analysis and

Prediction SystemLAMP Local AWIPS MOS

ProgramLAT LatitudeLCL LocalLCLY LocallyLCTD LocatedLCTN LocationLCTMP Little change in

temperatureLEVEL LevelLFTG LiftingLGRNG Long rangeLGT LightLGTR LighterLGWV Long waveLI Lifted IndexLIS Lifted indicesLK LakeLKS LakesLKLY LikelyLLJ Low Level JetLLWS Low Level Wind ShearLLWAS Low level wind shear

alert systemLMTD LimitedLMTG Limiti6ngLMTS LimitsLN LineLNS Lines

LO LowLONG LongitudeLONGL LongitudnalLRG LargeLRGLY LargelyLRGR LargerLRGST LargestLST Local standard timeLTD LimitedLTG LightningLTGCC Lightning cloud-to-

cloudLTGCG Lightning cloud-to-

groundLTGCCCG Lightning cloud-to-

cloud cloud-to-ground

LTGCW Lightning cloud-to-water

LTGIC Lightning in cloudLTL LittleLTLCG Little changeLTR LaterLTST LatestLV LeavingLVL LevelLVLS LevelsLWR LowerLWRD LoweredLWRG LoweringLYR LayerLYRD LayeredLYRS Layers

- M -

MA MassachusettsMAN ManitobaMAX MaximumMB MillibarsMCD Mesoscale discussionMD MarylandMDFY ModifyMDFYD Modified

MDFYG ModifyingMDL ModelMDLS ModelsMDT ModerateMDTLY ModeratelyME MaineMED MediumMEGG MergingMESO MesoscaleMET MeteorologicalMETRO MetropolitanMEX MexicoMHKVLY Mohawk ValleyMI Shallow (METAR code)MI MichiganMID MiddleMIDN MidnightMIL MilitaryMIN MinimumMISG MissingMLTLVL Melting levelMN MinnesotaMNLND MainlandMNLY MainlyMO MissouriMOGR Moderate or greaterMOS Model Output StatisticsMOV MoveMOVD MovedMOVG MovingMOVMT MovementMOVS MovesMPH Miles per hourMRGL MarginalMRGLLY MarginallyMRNG MorningMRTM MaritimeMS MississippiMSG MessageMSL Mean sea levelMST MostMSTLY MostlyMSTR MoistureMT MontanaMTN Mountain

MTNS MountainsMULT MultipleMULTILVL Multi-levelMXD Mixed

- N -

N NorthNAB Not aboveNAT North AtlanticNATL NationalNAV NavigationNB New BrunswickNBND NorthboundNBRHD NeighborhoodNC North CarolinaNCEP National Center for En-

vironmental PredictionNCWX No change in weatherND North DakotaNE NortheastNEB NebraskaNEC NecessaryNEG NegativeNEGLY NegativelyNELY NortheasterlyNERN NortheasternNEWD NortheastwardNEW ENG New EnglandNFLD NewfoundlandNGM Nested Grid ModelNGT NightNH New HampshireNHC National Hurricane

CenterNIL NoneNJ New JerseyNL No layersNLT Not later thanNLY NortherlyNM New MexicoNMBR NumberNMBRS NumbersNML Normal

NMRS NumerousNNE North-northeastNNELY North-northeasterlyNNERN North-northeasternNNEWD North-northeastwardNNW North-northwestNNWLY North-northwesterlyNNWRN North-northwesternNNWWD North-northwestwardNNNN End of messageNOAA National Oceanic and

Atmospheric Administration

NOPAC Northern PacificNPRS NonpersistentNR NearNRLY NearlyNRN NorthernNRW NarrowNS Nova ScotiaNTFY NotifyNTFYD NotifiedNV NevadaNVA Negative vorticity

advectionNW NorthwestNWD NorthwardNWLY NorthwesterlyNWRN NorthwesternNWS National Weather

ServiceNY New YorkNXT Next

- O -

OAT Outside Air Temperature

OBND OutboundOBS ObservationOBSC ObscureOBSCD ObscuredOBSCG ObscuringOCFNT Occluded front

OCLD OccludeOCLDS OccludesOCLDD OccludedOCLDG OccludingOCLN OcclusionOCNL OccasionalOCNLY OccasionallyOCR OccurOCRD OccurredOCRG OccurringOCRS OccursOFC OfficeOFP Occluded frontal

passageOFSHR OffshoreOH OhioOK OklahomaOMTNS Over mountainsONSHR On shoreOR OregonORGPHC OrographicORIG OriginalOSV Ocean station vesselOTLK OutlookOTP On topOTR OtherOTRW OtherwiseOUTFLO OutflowOVC OvercastOVNGT OvernightOVR OverOVRN OverrunOVRNG OverrunningOVTK OvertakeOVTKG OvertakingOVTKS Overtakes

- P -

PA PennsylvaniaPAC PacificPBL Planetary boundary

layerPCPN Precipitation

PD PeriodPDS PeriodsPDMT PredominantPEN PeninsulaPERM PermanentPGTSND Puget SoundPHYS PhysicalPIBAL Pilot balloon

observationPIBALS Pilot balloon reportsPIREP Pilot weather reportPIREPS Pilot weather reportsPL Ice pellets

(METAR code)PLNS PlainsPLS PleasePLTO PlateauPM Post meridianPNHDL PanhandlePO Well developed

dust/sand whirls(METAR code)

POS PositivePOSLY PositivelyPPINE PPI no echoesPPSN Present positionPR Partial (METAR code)PRBL ProbablePRBLY ProbablyPRBLTY ProbabilityPRECD PrecedePRECDD PrecededPRECDG PrecedingPRECDS PrecedesPRES PressurePRESFR Pressure falling rapidlyPRESRR Pressure rising rapidlyPRIM PrimaryPRIN PrincipalPRIND Present indications arePRJMP Pressure jumpPROC ProcedurePROD ProducePRODG ProducingPROG Forecast

PROGD ForecastedPROGS ForecastsPRSNT PresentPRSNTLY PresentlyPRST PersistPRSTS PersistsPRSTNC PersistencePRSTNT PersistentPRVD ProvidePRVDD ProvidedPRVDG ProvidingPRVDS ProvidesPS PlusPSBL PossiblePSBLY PossiblyPSBLTY PossiblityPSG PassagePSN PositionPSND PositionedPTCHY PatchyPTLY PartlyPTNL PotentialPTNLY PotentiallyPTNS PortionsPUGET Puget SoundPVA Positive vorticity

advectionPVL PrevailPVLD PrevailedPVLG PrevailingPVLS PrevailsPVLT PrevalentPWR PowerPY Spray (METAR code)

- Q -

QN QuestionQPFERD NCEP excessive

rainfall discussionQPFHSD NCEP heavy snow

discussionQPFSPD NCEP special precip-

itation discussion

QSTNRY QuasistationaryQUAD QuadrantQUE Quebec

- R -

R RainRA Rain (METAR code)RADAT Radiosonde

observation dataRAOB Radiosonde

observationRAOBS Radiosonde

observationsRCH ReachRCHD ReachedRCHG ReachingRCHS ReachesRCKY RockyRCKYS RockiesRCMD RecommendRCMDD RecommendedRCMDG RecommendingRCMDS RecommendsRCRD RecordRCRDS RecordsRCV ReceiveRCV ReceivedRCVG ReceivingRCVS ReceivesRDC ReduceRDGG RidgingRDR RadarRDVLP RedevelopRDVLPG RedevelopingRDVLPMT RedevelopmentRE RegardRECON ReconnaissanceREF ReferenceRES ReserveRGN Region RGT RightRI Rhode IslandRLBL Reliable

REPL ReplaceREPLD ReplacedREPLG ReplacingREPLS ReplacesREQ RequestREQS RequestsREQSTD RequestedRESP ResponseRESTR RestrictRGD RaggedRGLR RegularRGN RegionRGNS RegionsRH Relative HumidityRIOGD Rio GrandeRLTV RelativeRLTVLY RelativilyRMN RemainRMND RemainedRMNDR RemainderRMNG RemainingRMNS RemainsRNFL RainfallROT RotateROTD RotatedROTG RotatingROTS RotatesRPD RapidRPDLY RapidlyRPLC ReplaceRPLCD ReplacedRPLCG ReplacingRPLCS ReplacesRPRT ReportRPRTD ReportedRPRTG ReportingRPRTS ReportsRPT RepeatRPTG RepeatingRPTS RepeatsRQR RequireRQRD RequiredRQRG RequiringRQRS RequiresRS Receiver station

RSG RisingRSN ReasonRSNG ReasoningRSNS ReasonsRSTR RestrictRSTRD RestrictedRSTRG RestrictingRSTRS RestrictsRTRN ReturnRTRND ReturnedRTRNG ReturningRTRNS ReturnsRUC Rapid Update CycleRUF RoughRUFLY RoughlyRVS ReviseRVSD RevisedRVSG RevisingRVSS RevisesRW Rain shower

- S -

S SouthSA Sand (METAR code)SA Surface observationSAO Surface observationSAOS Surface observationsSASK SaskatchewanSATFY SatisfactorySBND South boundSBSD SubsideSBSDD SubsidedSBSDNC SubsidenceSBSDS SubsidesSC South CarolinaSCND SecondSCNDRY SecondarySCSL Standing lenticular

stratocumulusSCT ScatterSCTD ScatteredSCTR SectorSD South Dakota

SE SoutheastSEC SecondSELY SoutheasterlySEPN SeparationSEQ SequenceSERN SoutheasternSEWD SoutheastwardSFC SurfaceSFERICS AtmosphericsSG Snow grainsSGFNT SignificantSGFNTLY SignificantlySH Showers

(METAR code)SHFT ShiftSHFTD ShiftedSHFTG ShiftingSHFTS ShiftsSHLD ShieldSHLW ShallowSHRT ShortSHRTLY ShortlySHRTWV ShortwaveSHRTWVS ShortwavesSHUD ShouldSHWR ShowerSHWRS ShowersSIERNEV Sierra NevadaSIG SignatureSIGMET Significant meteorologi

cal informationSIMUL SimultaneousSKC Sky clearSKED ScheduleSLD SolidSLGT SlightSLGTLY SlightlySLO SlowSLOLY SlowlySLOR SlowerSLP SlopeSLPG SlopingSLT SleetSLY SoutherlySM Statute mile

SMK SmokeSML SmallSMLR SmallerSMRY Summary

SMS Synchronus meteorological satellite

SMTH SmoothSMTHR SmootherSMTHST SmoothestSMTM SometimeSMWHT SomewhatSN Snow (METAR code)SNBNK Snow bankSND SandSNFLK Snow flakeSNGL SingleSNOINC Snow increaseSNOINCRG Snow increasingSNST SunsetSNW SnowSNWFL SnowfallSOP Standard operating

procedureSP Snow pelletsSPC Storm Prediction Cent.SPCLY EspeciallySPD SpeedSPDS SpeedsSPENES Satellite precipitation

estimate statementSPKL SprinkleSPKLS SprinklesSPLNS Southern PlainsSPRD SpreadSPRDG SpreadingSPRDS SpreadsSPRL SpiralSQ Squall (METAR code)SQAL SquallSQLN Squall lineSR SunriseSRN SouthernSRND SurroundSRNDD Surrounded

SRNDG SurroundingSRNDS SurroundsSS Sandstorm

(METAR code)SS SunsetSSE South-southeastSSELY South-southeasterlySSERN South-southeasternSSEWD South-southeastwardSSW South-southwestSSWLY South-southwesterlySSWRN South-southwesternSSWWD South-southwestwardST StratusSTAGN StagnationSTBL StableSTBLTY StabilitySTD StandardSTDY SteadySTFR Stratus fractusSTFRM StratiformSTG StrongSTGLY StronglySTGR StrongerSTGST StrongestSTLT SatelliteSTM StormSTMS StormsSTN StationSTNS StationsSTNRY StationarySUB SubstituteSUBTRPCL SubtropicalSUF SufficientSUFLY SufficientlySUG SuggestSUGG SuggestingSUGS SuggestsSUP SupplySUPG SupplyingSUPR SuperiorSUPS SuppliesSUPSD SupersedeSUPSDG SupersedingSUPSDS Supersedes

SVG ServingSVR SevereSVRL SeveralSW SouthwestSWD SouthwardSWWD SouthwestwardSW- Light snow showerSW+ Heavy snow showerSWLG SwellingSWLY SouthwesterlySWODY1 SPC Severe Weather

Outlook for Day 1SWOMCD SPC Mesoscale

DiscussionSWRN SouthwesternSX Stability indexSXN SectionSXNS SectionsSYNOP SynopticSYNS SynopsisSYS System

- T -

T ThunderTCNTL TranscontinentalTCU Towering cumulusTDA TodayTEMP TemperatureTHD ThunderheadTHDR ThunderTHK ThickTHKNG ThickeningTHKNS ThicknessTHKR ThickerTHKST ThickestTHN ThinTHNG ThinningTHNR ThinnerTHNST ThinnestTHR ThresholdTHRFTR ThereafterTHRU ThroughTHRUT Throughout

THSD ThousandTHTN ThreatenTHTND ThreatenedTHTNG ThreateningTHTNS ThreatensTIL UntilTMPRY TemporaryTMPRYLY TemporarillyTMW TomorrowTN TennesseeTNDCY TendencyTNDCYS TendenciesTNGT TonightTNTV TentativeTNTVLY TentativelyTOPS TopsTOVC Top of overcastTPG ToppingTRBL TroubleTRIB TributaryTRKG TrackingTRML TerminalTRMT TerminateTRMTD TerminatedTRMTG TerminatingTRMTS TerminatesTRNSP TransportTRNSPG TransportingTROF TroughTROFS TroughsTROP TropopauseTRPCD Tropical continentalTRPCL TropicalTRRN TerrainTRSN TransitionTRW ThunderstormTRW+ Thunderstorm with

heavy rain showerTS Thunderstorm

(METAR code)TS Thunderstorm

with snowTS+ Thunderstorm

with heavy snowTSFR Transfer

TSFRD TransferedTSFRG TransferingTSFRS TransfersTSHWR ThundershowerTSHWRS ThundershowersTSNT TransientTSQLS ThundersquallsTSTM ThunderstormTSTMS ThunderstormsTSW Thunderstorm

with snow showersTSW+ Thunderstorm with

heavy snow showersTURBC TurbulenceTURBT TurbulentTWD TowardTWDS TowardsTWI TwilightTWRG ToweringTX Texas

- U -

UDDF Up and down draftsUN UnableUNAVBL UnavailableUNEC UnnecessaryUNKN UnknownUNL UnlimitedUNRELBL UnreliableUNRSTD UnrestrictedUNSATFY UnsatisfactoryUNSBL UnseasonableUNSTBL UnstableUNSTDY UnsteadyUNSTL UnsettleUNSTLD UnsettledUNUSBL UnusableUP Unknown precipitation

in automated observations (METAR code)

UPDFTS UpdraftsUPR Upper

UPSLP UpslopeUPSTRM UpstreamURG UrgentUSBL UsableUT UtahUVV Upward vertical velocityUVVS Upward vertical

velocitiesUWNDS Upper winds

- V -

VA Volcanic ash (METAR code)

VA VirginiaVAD Verlocity Azimuth

DisplayVARN VariationVC Vicinity (METAR code)VCNTY VicinityVCOT VFR conditions on topVCTR VectorVCTS Thunderstorms in the

VicinityVDUC VAS Data Utilization

Center (NSSFC)VFY VerifyVFYD VerifiedVFYG VerifyingVFYS VerifiesVLCTY VelocityVLCTYS VelocitiesVLNT ViolentVLNTLY ViolentlyVLY ValleyVLYS ValleysVMC Visual meteorological

conditionsVOL VolumeVORT VorticityVR VeerVRG VeeringVRBL VariableVRISL Vancouver Island, BC

VRS VeersVRT MOTN Vertical MotionVRY VeryVSB VisibleVSBY VisibilityVSBYDR Visibility decreasing

rapidlyVSBYIR Visibility increasing

rapidlyVT VermontVWP VAD Wind ProfilerVV Vertical velocity

- W -

W WestWA WashingtonWAA Warm Air AdvectionWBND West boundWDLY WidelyWDSPRD WidespreadWEA WeatherWFO Weather Forecast

OfficeWFOS Weather Forecast

OfficesWFP Warm front passageWI WisconsinWIBIS Will be issuedWINT WinterWK WeakWKDAY WeekdayWKEND WeekendWKNG WeakeningWKNS WeakensWKR WeakerWKST WeakestWKN WeakenWL WillWLY WesterlyWND WindWNDS WindsWNW West-northwestWNWLY West-northwesterly

WNWRN West-northwesternWNWWD West-northwestwardWO WithoutWPLTO Western PlateauWRM WarmWRMG WarmingWRN WesternWRMR WarmerWRMST WarmestWRMFNT Warm frontWRMFNTL Warm FrontalWRNG WarningWRNGS WarningsWRS WorseWSHFT Wind shiftWSHFTS Wind ShiftsWSR-88D NWS Dopplar RadarWSTCH Wasatch RangeWSW West-southwestWSWLY West-southwesterlyWSWRN West-southwesternWSWWD West-southwestwardWTR WaterWTRS WatersWTSPT WaterspoutWTSPTS WaterspoutsWUD WouldWV West VirginiaWVS WavesWW Severe Weather WatchWWAMKC SPC Status ReportWWD WestwardWWS Severe Weather

WatchesWX WeatherWY Wyoming

- X -

XCP ExceptXPC ExpectXPCD ExpectedXPCG ExpectingXPCS Expects

XPLOS ExplosiveXTND ExtendXTNDD ExtendedXTNDG ExtendingXTRM ExtremeXTRMLY Extremely

- Y -

YDA YesterdayYKN YukonYLSTN Yellowstone

- Z -

ZL Freezing drizzleZN ZoneZNS ZonesZR Freezing rain