Area Forecast Discussion
Issued by NWS Cheyenne, WY

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000
FXUS65 KCYS 281026
AFDCYS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
426 AM MDT THU AUG 28 2014

.SHORT TERM...(TODAY THROUGH SATURDAY)
ISSUED AT 425 AM MDT THU AUG 28 2014

PREDAWN WATER VAPOR IMAGERY SHOWED THE UPPER LOW OVER SOUTHERN WY/NORTHERN
CO. AT THE SURFACE...A FRONT EXTENDED FROM THE MID-ATLANTIC REGION ACROSS
THE TN VALLEY TO A LOW ALONG THE CENTRAL NE/KS BORDER THEN SOUTHWEST
TO ANOTHER LOW IN SOUTHEAST CO. A LARGE CLUSTER OF STRONG CONVECTION
DEVELOPED ALONG AND JUST NORTH OF THE FRONT OVER SOUTH CENTRAL/SOUTHEAST
NE. LIGHT SHOWERS WERE DEVELOPING AND MOVING SOUTHWEST FROM EAST CENTRAL
TO SOUTH CENTRAL WY.

THE 00Z CONSENSUS MODEL GUIDANCE WEAKENS THE UPPER LOW TO AN OPEN WAVE
THIS MORNING OVER THE HIGH PLAINS...PROGRESSING SLOWLY EAST INTO THE
CENTRAL GREAT PLAINS FRIDAY. CONVECTIVE COVERAGE TODAY WILL BE LESS
THAN THE PAST FEW DAYS WITH THE RISK FOR HEAVY RAINFALL FROM THE CENTRAL
PLAINS TO THE UPPER MS VALLEY. WRAPAROUND MOISTURE OVER NORTHERN AND
WESTERN PORTIONS OF THE CWA THIS MORNING WILL GRADUALLY SLIDE EAST
THIS AFTERNOON AND EARLY EVENING. THERE WILL BE ENOUGH INSTABILITY FROM
DAYTIME HEATING FOR SCATTERED SHOWERS/TSTORMS THIS AFTERNOON...ESPECIALLY
SOUTH OF A RAWLINS WY TO ALLIANCE NE LINE. HIGH TEMPERATURES TODAY WILL
BE SLIGHTLY WARMER WITH 70S FOR LOWER ELEVATIONS.

A FEW LINGERING SHOWERS OR TSTORMS OVER THE EXTREME SOUTHERN NE PANHANDLE
EARLY THIS EVENING. OTHERWISE...SUBSIDENCE AND DRIER MORE STABLE AIRMASS
WILL SPREAD WEST TO EAST WITH THE APPROACH AND PASSAGE OF A SHORTWAVE
RIDGE.

A WEAK SHORTWAVE OVER THE NORTHERN ROCKIES EARLY FRIDAY MORNING MAKES
A BEELINE FOR THE NORTHERN HIGH PLAINS FRIDAY AFTERNOON. MOISTURE WILL
BE LIMITED WITH MARGINAL INSTABILITY FOR ISOLATED AFTERNOON TSTORMS
OVER THE MOUNTAINS AND NEARBY PLAINS OF SOUTHEAST WY. HIGH TEMPERATURES
WILL WARM INTO THE 80S EAST OF THE LARAMIE RANGE...WITH 60S AND 70S
WEST. EXPECT TRANQUIL CONDITIONS FRIDAY NIGHT WITH THE PASSAGE OF
ANOTHER SHORTWAVE RIDGE.

LATEST MODELS CONTINUE TO DEPICT A MORE SIGNIFICANT UPPER TROUGH TAKING
SHAPE OVER THE GREAT BASIN AND PACIFIC NORTHWEST SATURDAY. A RATHER
STRONG PACIFIC COLD FRONT WILL BE MOVING THROUGH NORTHERN AND WESTERN
WY DURING THE AFTERNOON. 700MB WINDS INCREASE TO 35 KT FROM THE WEST
AND SOUTHWEST. PACIFIC MOISTURE WILL ALSO INCREASE BY LATE AFTERNOON
WITH WIDELY SCATTERED SHOWERS/TSTORMS DEVELOPING ALONG AND WEST OF A
CHADRON NE TO CHEYENNE WY LINE. A TIGHTER SURFACE PRESSURE GRADIENT
WILL CREATE RATHER BREEZY WEST TO SOUTHWEST WINDS. IT WILL BE A WARM
AFTERNOON WITH HIGHS IN THE 80S TO LOWER 90S FOR THE PLAINS...WITH 60S
AND 70S WEST.

.LONG TERM...(SATURDAY NIGHT THROUGH WEDNESDAY)
ISSUED AT 350 AM MDT THU AUG 28 2014

MEDIUM AND LONG RANGE MODELS IN GOOD AGREEMENT INTO EARLY NEXT WEEK.
THE MAIN FORECAST CONCERN WILL BE A BROAD UPPER LEVEL TROUGH AND
ASSOCIATED COLD FRONT FOR LATER THIS WEEKEND. THE COLD FRONT APPEARS
TO BE RATHER STRONG FOR THIS TIME OF THE YEAR...WITH GUSTY WINDS
POSSIBLE ALONG WITH RAIN SHOWERS/TSTORMS OVER MOST OF THE AREA.
CANNOT RULE OUT SOME SNOWFALL ACROSS THE HIGH MOUNTAINS AS THIS FRONT
MOVES ACROSS THE AREA SATURDAY NIGHT AND INTO EARLY SUNDAY. MODELS
IN GOOD AGREEMENT WITH THE TIMING...ALTHOUGH THE GFS IS NOTICEABLY
MORE PROGRESSIVE AND DRIER. PREFER THE ECMWF AND GEM AT THIS TIME
SINCE BOTH THESE MODELS DID BETTER WITH THIS LAST STORM SYSTEM 3
DAYS OUT IN TERMS OF TIMING AND EVOLUTION. INCREASED POP ABOVE 30
PERCENT ACROSS MOST OF THE FORECAST AREA FOR SCATTERED SHOWERS AND
ISOLATED TSTORMS. INCREASED WINDS AS WELL...ALTHOUGH MODEL
SOUNDINGS ARE SUGGESTING SUSTAINED WESTERLY WINDS BETWEEN 20 TO 30
MPH AND GUSTS AROUND 40 MPH. DID NOT INCREASE WINDS QUITE THAT
HIGH SINCE THE ECMWF SHOWS MUCH LOWER WIND SPEEDS SUNDAY AFTERNOON.
TEMPERATURES WILL REMAIN ON THE COOL SIDE AND GENERALLY IN THE
UPPER 60S TO UPPER 70S...WARMEST ACROSS THE NEBRASKA PANHANDLE.

MODELS THEN INDICATE A DRYING TREND FOR NEXT WEEK AS THE SOUTHWESTERN
MONSOON MAY BE ENDING...WHICH IS TYPICAL IN THE LATE SUMMER. MODELS
AND ENSEMBLES ALSO SHOW WHAT APPEARS TO BE A TRANSITIONAL PERIOD IN
THE PATTERN...AS THE POLAR JET STREAM BECOMES MORE DEFINED BY DAY
6 AND 7 NEAR THE CANADIAN BORDER. THIS WILL RESULT IN QUASI-ZONAL
FLOW OVER THE WESTERN TWO THIRDS OF THE UNITED STATES. HOWEVER...THE
ECMWF AND GEM DO SHOW AN UPPER LEVEL DISTURBANCE MOVING SOUTHEAST
ACROSS THE HIGH PLAINS LATE ON MONDAY...SO KEPT LOW POP OVER EAST
CENTRAL WYOMING AND NORTHWEST NEBRASKA. OTHERWISE...TEMPERATURES
WILL GRADUALLY INCREASE TO AROUND NORMAL FOR THIS TIME OF THE YEAR
WITH HIGHS AROUND 80 ALONG AND WEST OF THE LARAMIE RANGE AND RANGING
FROM THE LOW 80S TO THE LOW 90S ACROSS THE HIGH PLAINS EAST OF THE
LARAMIE RANGE BY WEDNESDAY AFTERNOON.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH LATE TONIGHT)
ISSUED AT 350 AM MDT THU AUG 28 2014

LOW CIGS WILL PERSIST EARLY THIS MORNING ACROSS MAINLY THE WESTERN
NEBRASKA PANHANDLE TERMINALS. FOG IS UNLIKELY AT THIS TIME DUE TO
CLOUD COVER. FOG AND LOW CIGS WILL LIFT BY MID MORNING WITH VFR
PREVAILING THROUGH NOON. THE NEXT BAND OF SHOWERS WILL DEVELOP AND
GROW IN COVERAGE EARLY THIS MORNING FROM RAWLINS TO LARAMIE. THIS
BAND WILL INTENSIFY AS THE UPPER LEVEL LOW GRADUALLY DRIFTS ACROSS
NORTHEAST COLORADO. THIS BAND OF RAINFALL AND EMBEDDED TSTORMS
WILL RESULT IN LOCALIZED MVFR CONDITIONS SOUTHEAST OF A KLAR TO
KCDR LINE BY LATE THIS MORNING AND INTO THIS AFTERNOON.

&&

.FIRE WEATHER...
ISSUED AT 255 AM MDT THU AUG 28 2014

THE UPPER LOW PRESSURE SYSTEM RESPONSIBLE FOR THE INCLEMENT WEATHER
THE PAST FEW DAYS WILL MOVE EAST FROM THE CENTRAL ROCKIES TODAY TO
THE CENTRAL GREAT PLAINS FRIDAY. A MORE SCATTERED COVERAGE OF SHOWERS
AND THUNDERSTORMS IS EXPECTED TODAY. MAINLY DRIER AND WARMER CONDITIONS
ARE FORECAST FOR FRIDAY WITH JUST A SLIGHT CHANCE OF AFTERNOON
THUNDERSTORMS OVER THE MOUNTAINS AND PORTIONS OF EAST CENTRAL WYOMING
WITH THE PASSAGE OF A WEAK UPPER LEVEL DISTURBANCE. ISOLATED TO
SCATTERED MAINLY AFTERNOON AND EVENING SHOWERS AND THUNDERSTORMS ARE
FORECAST SATURDAY AND SUNDAY AS A MORE SIGNIFICANT UPPER TROUGH AND
COLD FRONT AFFECT THE DISTRICTS. WARM TEMPERATURES SATURDAY WILL TURN
COOLER SUNDAY FOLLOWING THE COLD FRONTAL PASSAGE. THE TIGHT PRESSURE
GRADIENT WILL RESULT IN GUSTY WESTERLY WINDS THIS WEEKEND.

&&

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

$$

SHORT TERM...JAMSKI
LONG TERM...TJT
AVIATION...TJT
FIRE WEATHER...JAMSKI






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