Area Forecast Discussion
Issued by NWS Cheyenne, WY

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000
FXUS65 KCYS 281829
AFDCYS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
1229 PM MDT THU AUG 28 2014

.UPDATE...
ISSUED AT 1039 AM MDT THU AUG 28 2014

A VIGOROUS MIDLVL SHORTWAVE CONTINUES TO ROTATE ACROSS THE WESTERN
NE PANHANDLE THIS MORNING. WRAP-AROUND MOISTURE ON THE BACK SIDE
OF THIS SYSTEM IS CONTRIBUTING TO WIDESPREAD SHOWERS OR STRATIFORM
RAIN ALONG A LINE FROM CENTENNIAL TO WHEATLAND. HAVE RECENTLY SEEN
SOME HIGHER ECHOS IN CENTRAL PLATTE COUNTY...AS WELL AS SOME AREAS
ALONG THE WEST EDGE OF THE LARAMIE RANGE. 1-2 INCHES OF RAIN ON
WED MORNING AND AFTN LENDS SOME CONCERN TO FLOODING POTENTIAL IF
RATES ARE HIGH ENOUGH AND/OR WE SEE MORE TRAINING. FFMP DATA ALSO
SHOWS AREAS NORTHEAST OF BOSLER HAVE ALREADY RECEIVED CLOSE TO 2
INCHES OF RAIN TODAY. WILL CONTINUE TO MONITOR CLOSELY THROUGH
THE DAY FOR POSSIBLE STATEMENTS...BUT CURRENT WEBCAMS SUGGEST THE
GROUND IS ABSORBING THINGS WELL. ONGOING CLOUDS AND RAIN WILL MAKE
IT TOUGH TO REACH FCST HIGHS...SO IN A RECENT UPDATE HAVE CUT BACK
ON TEMPS BY 5-10 DEGREES WHERE MOST OF THE PRECIP IS OCCURRING PER
THE LATEST KCYS RADAR LOOP. ALSO BUMPED UP POPS INTO THE LIKELY
CATEGORY FOR FAR SOUTHEAST WY AND WESTERN NE...EXPANDING EASTWARD
WITH TIME.

&&

.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 18Z TAFS THROUGH 18Z FRIDAY MORNING)
ISSUED AT 1228 AM MDT THU AUG 28 2014

MAIN AVIATION CONCERNS TODAY WILL BE THE TIMING AND STRENGTH AS
BAND OF WRAP-AROUND RAIN SHOWERS AND EMBEDDED THUNDERSTORMS IMPACT
AREA TERMINALS. AT NOON...THIS BAND EXTENDED FROM NR KCDR/KAIA
SOUTHWEST TO KLAR. MVFR/IFR CIGS AND VSBS HAVE BEEN COMMON BENEATH
THIS AREA OF RAIN. IT WILL SLIDE EAST ACROSS THE KCYS...KBFF AND
KSNY THROUGH THE REST OF THE AFTERNOON. ALTHOUGH THE AREA HAS BEEN
FAIRLY COOL BENEATH THICK CLOUD-COVER...MAY SEE A FEW WEAK
EMBEDDED THUNDERSTORMS THIS AFTERNOON AS WELL. THIS BAND OF PRECIP
WILL SHIFT EAST OF ALL SITES BY 00Z...LEAVING CLEARING SKIES AND
VFR CONDITONS THRU THE REMAINDER OF THE PERIOD.

&&

.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.
&&

$$

UPDATE...HAMMER
SHORT TERM...JAMSKI
LONG TERM...TJT
AVIATION...HAHN
FIRE WEATHER...JAMSKI






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