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000
FXUS65 KCYS 150142
AFDCYS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
742 PM MDT TUE MAY 14 2013

.UPDATE...
ISSUED AT 738 PM MDT TUE MAY 14 2013

ISOLATED SHOWERS AND THUNDERSTORMS CONTINUE OVER THE NORTHERN
NEBRASKA PANHANDLE EARLY THIS EVENING WHILE MOST OF THE SHOWER AND
THUNDERSTORM ACTIVITY HAS DIED OFF OVER THE REST OF THE FORECAST
AREA. SHOWERS AND THUNDERSTORMS HAVE PRODUCED GUSTY WINDS.
TORRINGTON REPORTED A GUST OF 47 KTS WHILE THE ALLIANCE ASOS HIT
49 KTS. THE WIND GUST THREAT WILL QUICKLY SUBSIDE THIS EVENING AS
SHOWERS AND THUNDERSTORMS DIE OFF AND MOVE EAST OF THE AREA.

&&

.SHORT TERM...(TONIGHT THROUGH WEDNESDAY NIGHT)
ISSUED AT 234 PM MDT TUE MAY 14 2013

WIDESPREAD CUMULUS HAVE DEVELOPED ALONG THE SOUTHERN ZONES THIS
AFTERNOON IN A VERY DEEP BOUNDARY LAYER. RADAR IS SHOWING SOME
WEAK SHOWERS OUT THERE...HOWEVER ITS PROBABLY MOSTLY VIRGA WITH
GUSTY WINDS. THIS ISOLATED SHOWER ACTIVITY WILL LIKELY CONTINUE
INTO THE EVENING AS THE RUC SHOWS AROUND 100-200 J/KG OF CAPE
THROUGH AROUND 03Z.  LAPS ANALYSIS SHOWS A WEAK FRONT LOCATED FROM
DOUGLAS TO SIDNEY WITH HIGHER LLVL MOISTURE (DEWPOINTS IN THE 40S)
BEHIND IT AND THE MUCH DRIER AIR TO THE SOUTH OF IT. THE MODELS
HAVE THIS BOUNDARY PUSHING TO THE SOUTHWEST OVERNIGHT AND STALLING
ALONG THE LARAMIE RANGE IN THE MORNING. BOTH THE GFS AND NAM SHOW
SOME IMPRESSIVE LLVL MOISTURE BEING ADVECTED IN ON EAST-TO-
SOUTHEAST WINDS BY THE MORNING. INCREASED DEWPOINTS INTO THE LOW-
TO-MID 40S OVER THE PLAINS OF SOUTHEAST WY FROM WEDNESDAY MORNING
THROUGH THE AFTERNOON.

THE COMBINATION OF HIGHER LLVL MOISTURE AND SLIGHTLY COOLER
MIDLEVEL TEMPS ON WEDNESDAY AFTERNOON WILL RESULT IN GOOD SFC
INSTABILITY ALONG AND EAST OF THE LARAMIE RANGE. THE GFS AND NAM
BOTH SHOW LIFTED INDICES OF -3C TO -5C WHICH TRANSLATES INTO
1000-1250 J/KG OF CAPE. THE TREND OF THE MODELS HAS BEEN TO
INCREASE CONVECTIVE POTENTIAL AND QPF FOR WEDNESDAY AFTERNOON AND
EVENING. FOR THIS REASON...UP POPS INTO THE CHANCE CATEGORY OVER
THE MTNS AND PLAINS. THE DEEP LAYER SHEAR DOES NOT LOOK IMPRESSIVE
OVER THE SOUTHERN ZONES (AROUND 20 KTS)...HOWEVER FURTHER TO THE
NORTH ACROSS CONVERSE/NIOBRARA COUNTIES THE MIDLEVEL WINDS ARE
STRONGER AND 0-6KM SHEAR APPROACHES 40 KTS. SO IT LOOKS LIKE THAT
WILL BE THE REGION TO MONITOR FOR STRONGER STORMS WITH SOME SMALL
HAIL POTENTIAL. THE STORMS THAT DEVELOP OVER THE LARAMIE RANGE IN
THE EARLY AFTERNOON WILL PROGRESS EASTWARD INTO PORTIONS OF THE
WESTERN NEBRASKA PANHANDLE BY THE EARLY EVENING. TEMPS WILL BE
AROUND 10 DEGREES COOLER ON WEDNESDAY WITH THE MOIST SE SFC WINDS
AND GREATER CLOUD COVER.

.LONG TERM...(THURSDAY THROUGH MONDAY)
ISSUED AT 234 PM MDT TUE MAY 14 2013

THURSDAY...WEAK SHORTWAVE RIDGING ALOFT. WILL SEE ISOLATED AFTERNOON
AND EVENING THUNDERSTORMS...PRIMARILY ORIENTED ALONG THE SURFACE
TROUGH AXIS FROM EASTERN WYOMING SOUTHWARD THROUGH EASTERN COLORADO.

FRIDAY...FLOW ALOFT BACKS TO SOUTHWEST IN ADVANCE OF NEXT SHORTWAVE
TROUGH ALOFT. QUITE WARM WITH A DECENT LOW LEVEL THERMAL RIDGE
ORIENTED NORTH TO SOUTH ALONG A DECENT SURFACE TROUGH OVER OUR
COUNTIES. ISOLATED AFTERNOON AND EVENING THUNDERSTORMS ALONG A LOW
LEVEL CONVERGENCE AXIS FROM CASPER TO CHADRON TO SIDNEY...WITH AREAL
COVERAGE OF THUNDERSTORMS MINIMIZED BY WARM TEMPERATURES ALOFT
PROVIDING SIGNIFICANT CONVECTIVE INHIBITION...CIN.

SATURDAY...DECENT NEGATIVELY TILTED SHORTWAVE TROUGH ALOFT ROTATES
EASTWARD ACROSS OUR COUNTIES AND ALONG WITH ITS ASSOCIATED PACIFIC
ORIGIN COLD FRONT...EXPECT ISOLATED TO SCATTERED AFTERNOON AND
EVENING THUNDERSTORMS...MOST NUMEROUS NEAR THE MOUNTAINS DUE TO
DIFFERENTIAL HEATING AND OROGRAPHIC EFFECTS.

SUNDAY...A DEFINITE BRITISH ISLES COASTAL FEEL TYPE DAY. BRISK
WINDS...COOLER TEMPERATURES AND ISOLATED TO SCATTERED AFTERNOON AND
EVENING SHOWERS AND THUNDERSTORMS ON TAP WITH NORTHWEST FLOW ALOFT
AND ENOUGH LOW AND MID LEVEL MOISTURE TO BE LIFTED BY DAYTIME
HEATING EFFECTS AND CYCLONIC FLOW ALOFT. LOW LEVEL DOWNSLOPE WINDS
WILL PRODUCE A RAIN SHADOW EFFECT FROM WHEATLAND TO CHEYENNE AND
MINIMIZE PRECIPITATION COVERAGE.

MONDAY...REFRESHINGLY COOL START TO THE TRADITIONAL WORKWEEK IN THE
WAKE OF THE RELATIVELY STRONG SHORTWAVE TROUGH PASSAGE AND WITH COOL
NORTH WINDS IN USHERING IN RELATIVELY COOL CANADIAN AIR. ISOLATED
AFTERNOON SHOWERS AND THUNDERSTORMS. TEMPERATURES WILL STILL BE NEAR
NORMAL THOUGH.

TUESDAY...TRANSITORY SHORTWAVE RIDGE ALOFT MOVES ACROSS OUR COUNTIES
AND ALONG WITH MUCH LESS LOW AND MID LEVEL MOISTURE...ONLY ISOLATED
AFTERNOON AND EVENING THUNDERSTORMS EXPECTED.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z WEDNESDAY AFTERNOON)
ISSUED AT 402 PM MDT TUE MAY 14 2013

VFR PREVAILS.

THROUGH 02Z TONIGHT...ISOLATED HIGH BASED SHOWERS AND THUNDERSTORMS
WILL AFFECT THE LARAMIE AND CHEYENNE TAFS WITH GUSTY AND ERRATIC
WINDS AS ISOLATED SHOWERS AND THUNDERSTORMS DEVELOP OVER AND NEAR
THE SNOWY...SIERRA MADRE AND SOUTHERN LARAMIE RANGES. SHOWERS AND
THUNDERSTORMS WILL PRODUCE LOCALIZED TURBULENCE.

PERIODS OF SCATTERED TO BROKEN LOW AND MIDDLE CLOUDS AT OR ABOVE
6000 FEET AGL.

A WEAK COLD FRONT WILL MOVE SOUTHWESTWARD TO THE LEE OF THE LARAMIE
RANGE THIS EVENING. SURFACE HIGH PRESSURE WILL MOVE INTO SOUTH
DAKOTA TONIGHT PRODUCING WEAK LOW LEVEL UPSLOPE SOUTH AND
SOUTHEAST WINDS ACROSS TAF SITES. LOW LEVEL SOUTH AND SOUTHEAST
WINDS WILL STRENGTHEN WEDNESDAY MORNING...WITH SCATTERED CUMULUS
AND TOWERING CUMULUS DEVELOPMENT ALONG AND WEST OF INTERSTATE 25
BY LATE MORNING...ALONG WITH ISOLATED THUNDERSTORMS IN THIS AREA
TOWARDS NOON. SCATTERED SHOWERS AND THUNDERSTORMS WILL DEVELOP
OVER SOUTHEAST WYOMING AFTER NOON WEDNESDAY PRODUCING LOCALIZED
MVFR AND ERRATIC AND GUSTY WINDS TO 50 MPH.


&&

.FIRE WEATHER...
ISSUED AT 234 PM MDT TUE MAY 14 2013

RELATIVE HUMIDITY VALUES HAVE DROPPED BELOW 15 PERCENT THIS
AFTERNOON ACROSS MUCH OF THE LOWER ELEVATIONS IN A VERY WARM
AIRMASS. WINDS HAVE BECOME WEAK NORTHERLY OVER THE PANHANDLE
BEHIND A WEAK FRONT...WITH GUSTS GENERALLY BELOW 20 MPH.
TEMPERATURES ON WEDNESDAY ARE EXPECTED TO BE AROUND 10 DEGREES
COOLER WITH SOUTHEAST WINDS ALONG AND EAST OF THE LARAMIE RANGE.
THE INCREASING LOW LEVEL MOISTURE WILL PROMOTE SCATTERED SHOWERS
AND THUNDERSTORMS ON WEDNESDAY AFTERNOON AND EVENING.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...NONE.
NE...NONE.
&&

$$

UPDATE...LIEBL
SHORT TERM...FINCH
LONG TERM...RUBIN
AVIATION...RUBIN
FIRE WEATHER...FINCH