Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 301809 AAA
AFDCYS

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE CHEYENNE WY
1208 PM MDT SAT AUG 30 2014

.SHORT TERM...(TODAY THROUGH MONDAY)
ISSUED AT 335 AM MDT SAT AUG 30 2014

CURRENT IR SATELLITE LOOP SHOWS MOSTLY CLEAR SKIES OVER THE
FORECAST AREA AS THE NEXT BROAD UPPER LEVEL TROUGH IS CURRENTLY
PUSHING ACROSS THE PACIFIC NORTHWEST EARLY THIS MORNING. WITH
EASTERLY WINDS OVER THE HIGH PLAINS AND CLEAR SKIES...HAVE TO
MONITOR THE POTENTIAL OF SOME PATCHY FOG EARLY THIS MORNING.
OTHERWISE...A WARM AND PLEASANT DAY IS EXPECTED FOR THE BEGINNING
OF THE HOLIDAY WEEKEND AS HIGH TEMPERATURES INCREASE INTO THE
UPPER 70S TO UPPER 80S THIS AFTERNOON. WESTERN NEBRASKA LOCATIONS
WILL LIKELY SEE READINGS AROUND 90 DEGREES THIS AFTERNOON. THE
UPPER LEVEL TROUGH AND ASSOCIATED COLD FRONT ARE TRENDING A LITTLE
SLOWER COMPARED TO 24 HOURS AGO...WITH MODELS INDICATING THE FRONT
SLOWLY MOVING ACROSS NORTHWEST WYOMING TODAY. THUNDERSTORMS MAY BE
SLOW TO FORM...BUT EXPECT WIDELY SCATTERED SHOWERS AND TSTORMS
DEVELOPING FROM WEST TO EAST ACROSS THE AREA. MOST OF WESTERN
NEBRASKA WILL NOT SEE ANY CONVECTIVE ACTIVITY UNTIL THIS EVENING
DUE TO A WEAK CAP INVERSION AND DRIER AIR ALOFT. THIS FRONT WILL
EVENTUALLY ACCELERATE EASTWARD LATE TONIGHT RESULTING IN AT LEAST
ISOLATED SHOWERS AND TSTORMS AS A STRONGER THAN NORMAL 105 KT JET
MOVES OVER THE WYOMING/COLORADO BORDER.

EXPECT A COOLER THAN AVERAGE DAY ON SUNDAY BEHIND THE COLD FRONT
AS THE TROUGH AXIS MOVES ACROSS THE AREA AND 700MB TEMPERATURES
LOWER BETWEEN 4C TO 8C...RESULTING IN SURFACE TEMPERATURES IN THE
UPPER 60S TO MID 70S ACROSS MOST OF THE FORECAST AREA. WITH A
STRONG JET OVER THE AREA...BELIEVE MODELS ARE DOWNPLAYING THE
COVERAGE OF SHOWERS AND TSTORMS ON SUNDAY. INCREASED POP BETWEEN
25 TO 40 PERCENT ACROSS MOST OF THE REGION WITH SCATTERED SHOWERS
AND SOME THUNDER. WINDY CONDITIONS ARE EXPECTED THIS
WEEKEND...ESPECIALLY WEST OF THE LARAMIE RANGE WITH GUSTS UP TO 45
MPH POSSIBLE. SHOWER ACTIVITY WILL QUICKLY COME TO AN END SUNDAY
EVENING AS DRIER AIR AND MORE STABLE CONDITIONS MOVE OVER THE
FORECAST AREA.

ANOTHER COOL DAY EXPECTED ON MONDAY WITH HIGHS STRUGGLING TO REACH
THE LOW TO MID 70S ACROSS MOST OF THE AREA. THERE IS SOME MODEL
DISAGREEMENT DURING THE DAY WITH THE ECMWF SHOWING A SECONDARY
SHORTWAVE TROUGH QUICKLY MOVING OVER THE AREA. THE GFS...NAM AND
GEM EITHER SHOW THIS FEATURE FURTHER TO THE NORTH OR MUCH WEAKER
COMPARED TO THE ECMWF. KEPT A SLIGHT CHANCE OF SHOWERS IN THE
FORECAST FOR NOW...WITH POP AROUND 20 PERCENT ACROSS THE MOUNTAINS
AND HIGH PLAINS.

.LONG TERM...(MONDAY NIGHT THROUGH FRIDAY NIGHT)
ISSUED AT 300 AM MDT SAT AUG 30 2014

WARM...WINDY AND DRY WILL BE THE MAIN WEATHER STORY THROUGH MUCH
OF THE EXTENDED FORECAST PERIOD. MONDAY NIGHT WILL START OFF WITH
A FAST MOVING SHORTWAVE PUSHING EAST OF THE FORECAST AREA. THERE
MAY BE A FEW EVENING SHOWERS DEPENDING ON THE TIMING OF THE
SHORTWAVE... OTHERWISE A VAST MAJORITY OF THE AREA WILL BE DRY TUE
AND WED AS WESTERLY DOWNSLOPE FLOW KICKS IN ALONG WITH RIDGING
OVER THE WESTERN CONUS. WITH WARM AND DRY CONDITIONS IN PLACE
GUSTY WINDS WILL LIKELY PRODUCE CRITICAL FIRE WEATHER CONDITIONS.

QUESTIONS BEGIN TO ARISE THUR AND FRI AND EXTENDED MODELS DIVERGE.
GFS SHOWING A MUCH MORE PRONOUNCE TROUGH ACROSS THE FAR WESTERN
PORTIONS OF THE CONUS WITH A WEAK SHORTWAVE BRINGING MOISTURE INTO
SOUTHEAST WYOMING FOR THURSDAY. THE EC KEEPS WESTERLY FLOW WITH A
WEAK TROUGH DIGGING INTO THE NORTHWEST CONUS WHICH WOULD MEAN DRY
THROUGH THURSDAY.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z SUNDAY MORNING)
ISSUED AT 12 PM MDT SAT AUG 30 2014

SHORT TERM FORECAST TRENDS STILL SUGGEST THAT WE WILL SEE ISOLATED
SHOWERS AND THUNDERSTORMS FORMING IN THE HIGHER TERRAIN WEST OF
CHEYENNE IN THE MID AFTERNOON HOURS. LATEST HIGH RESOLUTION RAPID
REFRESH MODEL RUNS DEVELOP CONVECTION AROUND RAWLINS AND LARAMIE
AROUND 21Z...WORKING IT EASTWARD ACROSS THE CHEYENNE AREA MID TO LATE
AFTERNOON...THEN WEAKENING IT AS IT MOVES INTO THE MORE HIGHLY
CAPPED ATMOSPHERE OVER THE NEBRASKA PANHANDLE 00Z-03Z. HRRR
TIMING CLOSE TO OUR THINKING AS WELL ON TIMING FOR
SHOWERS/THUNDERSTORMS IN VICINITY OF EACH FORECAST LOCATION. DIDNT
MENTION VICINITY THUNDERSTORMS AT ALLIANCE AND SYDNEY DUE TO
GREATER CAP IN THE EAST. CEILINGS AND VISIBILITIES PREVAILING VFR
ALL PERIODS. COVERAGES OF SHOWERS AND STORMS NOT HIGH ENOUGH THIS
AFTERNOON AND EVENING FOR PREVAILING MENTION BELOW VFR CATEGORY.

&&

.FIRE WEATHER...
ISSUED AT 236 AM MDT SAT AUG 30 2014

NO SIGNIFICANT FIRE WEATHER CONCERNS THIS WEEKEND AND INTO EARLY
NEXT WEEK. A STRONG WEATHER DISTURBANCE AND ASSOCIATED COLD FRONT
WILL MOVE ACROSS THE AREA LATE TODAY THROUGH EARLY SUNDAY. SHOWERS
AND TSTORMS WILL DEVELOP FROM WEST TO EAST ACROSS SOUTHEAST WY
AND MOVE THE WESTERN NEBRASKA. GUSTY WEST TO SOUTHWEST WINDS ARE
EXPECTED ALONG AND WEST OF THE LARAMIE RANGE THIS WEEKEND WITH
GUSTS BETWEEN 30 TO 40 MPH. MINIMUM HUMIDITIES WILL REMAIN ABOVE
20 PERCENT HOWEVER INTO MONDAY WITH COOLER THAN NORMAL
TEMPERATURES.

&&

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

$$

SHORT TERM...TJT
LONG TERM...SML
AVIATION...GARMON
FIRE WEATHER...TJT






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