Area Forecast Discussion
Issued by NWS Cheyenne, WY

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000
FXUS65 KCYS 231718
AFDCYS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
1118 AM MDT WED JUL 23 2014

.UPDATE...
ISSUED AT 850 AM MDT WED JUL 23 2014

EAST UPSLOPE FLOW IS CURRENTLY HOLDING THE LOW CLOUDS IN PLACE
ACROSS MUCH OF SOUTHEAST WYOMING EAST OF THE LARAMIE RANGE AND
INTO PARTS OF THE NEBRASKA PANHANDLE. LOW CLOUDS SHOULD MIX OUT BY
LATE THIS MORNING. NOT EXPECTING A BIG IMPACT ON HIGH TEMPERATURES
OR CHANCES FOR THUNDERSTORMS TODAY. ISOLATED CONVECTION
TO DEVELOP OVER THE MOUNTAINS BY EARLY THIS AFTERNOON. LOW CLOUDS
AND STABLE MID LEVEL AIR LEFT BEHIND FORM LAST NIGHTS
THUNDERSTORMS WILL INITIALLY INHIBIT EASTWARD MOVEMENT OF
THUNDERSTORMS INTO THE PLAINS. ONE THING OF NOTE IS THE STABLE
LAYER THAT IS IN PLACE MAY BE STRONGER THAN MODELS SUGGEST...WHICH
COULD HAVE A BROADER IMPACT ON DECREASING THUNDERSTORM CHANCES.

AT THIS TIME IS APPEARS THE MAIN CHANCES FOR THUNDERSTORMS IN THE
PLAINS WILL BE LATE THIS AFTERNOON AND EVENING WITH THE GREATEST
THREAT INTO EAST CENTRAL WYOMING AND THE NORTHERN NEBRASKA
PANHANDLE. THIS IS ALSO WHERE THE MAIN THREAT FOR SEVERE
THUNDERSTORMS WILL BE GIVEN A STRONGER SHEAR PROFILE AND HIGHER
CAPE VALUES. MAIN THREAT WILL BE THE LARGE HAIL BUT STRONG WINDS
AND AN AN ISOLATED TORNADO POSSIBLE. WITH ANY LUCK MOST
THUNDERSTORM ACTIVITY IN THE PLAINS WILL HOLD OFF UNTIL LATE THIS
EVENING AS THE LOW LEVEL JET RAMPS UP AND STRONGER MID LEVEL
THETAE ADVECTION KICKS IN. THIS WILL MAKE FOR THE MAIN THUNDERSTORM
CHANCES TOWARD CHADRON AND POINTS NORTH AND EAST OF THE FORECAST
AREA.

&&

.SHORT TERM...(TODAY THROUGH FRIDAY)
ISSUED AT 300 AM MDT WED JUL 23 2014

LOTS OF FORECAST CHALLENGES WITH THIS FORECAST PACKAGE...RANGING
FROM SEVERE CONVECTIVE WEATHER TODAY TO FIRE WEATHER CONCERNS
THURSDAY AND FRIDAY.

CURRENTLY...THE MUCH ANTICIPATED COLD FRONT DID MOVE INTO THE AREA
LAST EVENING AND IS CURRENTLY LOCATED GENERALLY ALONG A LINE FROM
CASPER...ALONG THE LARAMIE RANGE DOWN TO LARAMIE AND THEN INTO
NORTHEASTERN COLORADO. THIS FRONT IS SEPARATING VERY MOIST AIR
EAST OF THE FRONT...CHEYENNE HAS A 1AM DEWPOINT OF 57F/LARAMIE
55F...FROM VERY DRY AIR OUT OVER CARBON COUNTY WHERE THE DEWPOINT
AT RAWLINS IS 29F. THIS FEATURE IS GOING TO PLAY A MAJOR ROLE IN
TODAYS FORECAST WEATHER.

FOR TODAY...FRONT IS GOING TO REMAIN AT ITS CURRENT LOCATION
THROUGH THE MORNING HOURS BEFORE IT STARTS TO GET FORCED EAST WITH
INCREASING WESTERLY FLOW. LATEST HRRR FORECAST COMPOSITE
REFLECTIVITY HAS CONVECTION INITIATING ACROSS ALBANY COUNTY AND
THE SOUTH LARAMIE RANGE RIGHT AROUND 20Z TODAY DURING PEAK
HEATING. NAM SOUNDING FOR CHEYENNE HAS CAPE AROUND 1300 J/KG AT
THAT TIME WITH NO CONVECTIVE INHIBITION. PANHANDLE STAYS CAPPED A
LITTLE LONGER...NOT BREAKING THE CAP UNTIL AFTER 00Z. MUCH MORE
UNSTABLE OUT THERE WITH CHADRON NAM SOUNDING SHOWING SBCAPE CLOSE
TO 3500 J/KG. THINK DAY 1 SPC SLIGHT RISK AREA IS PRETTY
GOOD...BUT DO THINK THE LARAMIE COUNTY IS GOING TO SEE SOME SEVERE
THUNDERSTORMS AS WELL AND HAVE TAILORED OUR FORECAST WITH LARAMIE
COUNTY EXPERIENCING SEVERE THUNDERSTORMS THIS AFTERNOON. SEVERE
THUNDERSTORMS INITIALLY OVER THE SOUTHEAST WYOMING PLAINS...THEN
SPREADING EAST INTO THE PANHANDLE AFTER 00Z...AS THE FRONT MOVES
EAST AS A DRY LINE.

FOR THURSDAY...UPPER LOW MOVES INTO MONTANA THURSDAY AFTERNOON
WITH 700MB WINDS INCREASING OVER WYOMING. BY 18Z GFS 700MB WINDS
INCREASE TO 25-30KTS OVER CARBON AND ALBANY COUNTIES. BOTH THE GFS
AND ECMWF SHOW A UPPER LEVEL SHORTWAVE TRACKING THROUGH THE UPPER
RIDGE ALONG THE COLORADO/WYOMING LINE THAT WILL INTERACT WITH SOME
RESIDUAL MONSOONAL MOISTURE TO CREATE AFTERNOON THUNDERSTORMS. GFS
HAS PRECIP MAINLY OVER COLORADO...WHILE ECMWF SPREAD THIS MOISTURE
NORTH INTO WYOMING. DID A BLEND OF THE TWO MODELS WITH CHANCE
SHOWERS AND THUNDERSTORMS OVER SOUTHERN WYOMING NEAR THE COLORADO
BORDER, FORECAST SOUNDING SHOW THE POSSIBILITY OF DRY
THUNDERSTORMS OUT WEST OF THE LARAMIE RANGE THAT HAS ME A LITTLE
WORRIED ABOUT FIRE STARTS AS AFTERNOON MIN HUMIDITIES FALL TO 10
PERCENT ACROSS CARBON...NORTH ALBANY AND WEST CONVERSE COUNTIES.
WENT AHEAD WITH A FIRE WEATHER WATCH FOR THURSDAY FOR CONVERSE
COUNTY AS THIS AREA LOOKS TO BE THE BEST FOR A COMBINATION OF LOW
HUMIDITIES...GUSTY WINDS AND DRY THUNDERSTORMS.

GUSTY WEST WINDS CONTINUE INTO FRIDAY WITH VERY DRY DOWNSLOPING
WINDS OFF THE LARAMIE RANGE. COULD BE LOOKING AT WIDESPREAD FIRE
WEATHER CONDITIONS FRIDAY.

.LONG TERM...(FRIDAY NIGHT THROUGH TUESDAY)
ISSUED AT 240 AM MDT WED JUL 23 2014

MODELS GENERALLY IN GOOD AGREEMENT THROUGH THE WEEKEND WITH THE
OVERALL PATTERN...SHOWING A POTENT UPPER LEVEL TROUGH DIGGING
SOUTHWARD OUT OF CANADA AND INTO THE GREAT LAKES REGION BY EARLY
SUNDAY. THIS WILL RESULT IN NORTHWEST FLOW OVER THE FORECAST AREA
AS THE STRONG UPPER LEVEL HIGH NUDGES SOUTHWARD AND THE
ASSOCIATED RIDGE AXIS WILL EXTEND NORTHWEST INTO THE GREAT BASIN
REGION. THERE ARE STILL DISCREPANCIES BETWEEN MODELS REGARDING
AVAILABLE LOW TO MIDLEVEL MOISTURE THROUGH THE WEEKEND AND INTO
EARLY NEXT WEEK. ALTHOUGH A SERIES OF COOL FRONTS ARE EXPECTED TO
PUSH SOUTHWARD ACROSS THE FORECAST AREA BEGINNING FRIDAY
NIGHT...THE LACK OF ANY DEFINED DISTURBANCES IS CREATING QUITE A
BIT OF UNCERTAINTY WITH TSTORM CHANCES INTO MONDAY. CURRENT 00Z
MODELS ARE BEGINNING TO TREND DRIER...AS THE NORTHWEST FLOW
RESULTS IN A BIT MORE STABILITY THAN PREVIOUSLY EXPECTED...NUDGING
THE MONSOON MOISTURE FURTHER SOUTH INTO THE FOUR CORNERS REGION
AND COLORADO. STARTED TO LOWER POP FOR THIS WEEKEND ACROSS MOST OF
THE AREA...ESPECIALLY FURTHER NORTH SINCE THE ECMWF IS NOW
TRENDING DRIER AS WELL. CURRENT SOUNDINGS SHOW TOO MUCH DRY AIR
ALOFT...SUPPRESSING ANY CONVECTION THAT DOES FORM. AFTER ANOTHER
WARM DAY ON SATURDAY...EXPECT TEMPERATURES TO LOWER BELOW NORMAL
ON SUNDAY WITH HIGHS IN THE 70S TO MID 80S UNDER COOL EAST TO
NORTHEAST FLOW.

CONDITIONS BECOME A LITTLE MORE INTERESTING AFTER MONDAY AS BOTH
THE GFS AND ECMWF SHOW SHORTWAVE ENERGY MOVING CLOCKWISE AROUND
THE MAIN UPPER LEVEL HIGH AND INTO WYOMING. INCREASED POP LATE MONDAY
THROUGH WEDNESDAY...MAINLY IN THE AFTERNOON AND EVENINGS. BOTH THE
GFS AND ECMWF ARE ON THE AGGRESSIVE SIDE WITH A HIGHER COVERAGE OF
SHOWERS AND TSTORMS...AT LEAST SCATTERED DURING THE AFTERNOON...AS
THE SHORTWAVE ENERGY PUSHES ACROSS EASTERN WYOMING BY WEDNESDAY.
KEPT TEMPERATURES A FEW DEGREES BELOW NORMAL DUE TO EASTERLY
UPSLOPE FLOW AND 700MB TEMPERATURES LOWERING TO BELOW 10C.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z THURSDAY AFTERNOON)

VFR EXPECTED OVERALL FOR ALL AERODROMES THROUGH THURSDAY.  ISOLATED
SHOWERS AND TSTRMS OVER THE PLAINS THIS AFTERNOON AND EVENING WITH
ASSOCIATED MVFR VSBYS BUT LOOKING TOO ISOLATED TO MENTION IN
INDIVIDUAL TAFS.

&&

.FIRE WEATHER...
ISSUED AT 300 AM MDT WED JUL 23 2014

DRY CONDITIONS ACROSS WESTERN CARBON COUNTY AGAIN TODAY. A COLD
FRONT GENERALLY ALONG A LINE FROM CASPER TO LARAMIE WILL SEPARATE
RELATIVELY MOIST AIR EAST OF THE FRONT FROM THE REALLY DRY AIR TO
THE WEST. WETTING RAINS ARE LIKELY IN THE EASTERN SECTOR TODAY AND
TONIGHT WITH EXCELLENT OVERNIGHT RH RECOVERIES. CONDITIONS CHANGE
FOR THURSDAY THOUGH AS THE FRONT BEGINS TO MOVE EAST AGAIN AND
WINDS BEGIN TO PICK UP WEST OF THE LARAMIE RANGE. CRITICAL FIRE
WEATHER CONDITIONS FROM GUSTY WINDS AND LOW HUMIDITIES EARLY
THURSDAY AFTERNOON. TO COMPLICATE THE CONDITIONS MORE...WE HAVE
THE POSSIBILITY OF DRY THUNDERSTORMS WEST OF THE LARAMIE RANGE
THAT COULD CREATE SOME FIRE STARTS THURSDAY AFTERNOON. A FIRE
WEATHER WATCH HAS BEEN ISSUED FOR FWZ 301 FOR THURSDAY LATE
MORNING THROUGH THE AFTERNOON. DRY AND WINDY CONDITIONS TO
CONTINUE INTO SATURDAY FOR MORE WIDESPREAD FIRE WEATHER CONDITIONS
ACROSS SOUTHEAST WYOMING.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...FIRE WEATHER WATCH FROM THURSDAY MORNING THROUGH THURSDAY
     AFTERNOON FOR WYZ301.

NE...NONE.

&&

$$

UPDATE...SML
SHORT TERM...CLAYCOMB
LONG TERM...TJT
AVIATION...RE
FIRE WEATHER...CLAYCOMB





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