Area Forecast Discussion
Issued by NWS Cheyenne, WY

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000
FXUS65 KCYS 312145
AFDCYS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
345 PM MDT SUN AUG 31 2014

.SHORT TERM...(THIS EVENING THROUGH TUESDAY NIGHT)
ISSUED AT 345 PM MDT SUN AUG 31 2014

WATER VAPOR IMAGERY THIS AFTERNOON SHOWS THE UPPER LEVEL SHORTWAVE
MOVING OVER THE FORECAST AREA WITHIN THE LEFT EXIT REGION OF A 100
KT JET. AS OF 3 PM...THE SFC COLD FRONT LOOKS TO EXTEND ROUGHLY
FROM SOUTHEAST NIOBRARA COUNTY...THROUGH CONVERSE COUNTY...AND
WESTWARD THROUGH NATRONA COUNTY AND IS STEADILY MOVING SOUTH.
SCATTERED TO NUMEROUS SHOWERS AND T-STORMS HAVE DEVELOPED ACROSS
NORTHERN PORTIONS OF THE FORECAST AREA THIS AFTERNOON WITHIN THE
STRONGEST UPPER LEVEL AND SFC FORCING...WITH A FEW UPDRAFTS
SPIKING ABOVE 20KFT WITH THE HELP OF 500 TO 1000 J/KG OF MLCAPE.
MAINTAINED MENTION IN THE FORECAST FOR GUSTY WINDS AND SMALL HAIL
WITH THIS ACTIVITY THROUGH THE LATE AFTERNOON. 30 TO 40 KTS OF
BULK SHEAR IS ANALYZED OVER THE NEB PANHANDLE COINCIDENT WITH THE
HIGHER VALUES OF INSTABILITY...SO THE POSSIBILITY DOES EXIST FOR A
FEW STORMS TO BECOME STRONGER AS THEY TREK EAST TOWARD THE
SANDHILLS. WEAKER CONVECTION ALSO DEVELOPED OVER THE MOUNTAINS OF
SOUTHEAST WYOMING AND COLORADO EARLIER...WITH SOME OF THIS ACTIVITY
MOVING OFF THE HIGH TERRAIN AND ALONG THE CHEYENNE RIDGE AS WELL.
WATER VAPOR IMAGERY AND SPC MESOANALYSIS DATA INDICATE A BROADER
AREA OF SUBSIDENCE WAS OVER THIS AREA DURING THIS TIME...AND
LIKELY STUNTED THE GROWTH OF THE CONVECTION WHILE FORCING SOME
STRONGER WIND GUSTS AROUND 50 MPH TO THE SFC. A FEW SHOWERS
CONTINUE TO DEVELOP OVER MOUNTAINS AT THIS HOUR...BUT EXPECT A
SIMILAR TREND FOR WEAK BUT GUSTY SHOWERS AS DRIER AIR AND SOME
UPPER LEVEL SUBSIDENCE REMAIN IN PLACE HERE.

THE FRONT WILL CONTINUE TO MOVE SOUTH ACROSS EASTERN COUNTIES
THROUGH THIS EVENING WHILE DRIER AIR MOVES OVERHEAD AND SUBSIDENCE
BECOMES MORE WIDESPREAD. THUS EXPECT ACTIVITY TO COME TO AN END
QUICKLY AROUND SUNSET. ANOTHER SHORTWAVE WILL MOVE OVERHEAD TOMORROW
AFTERNOON...ALTHOUGH A MUCH DRIER AIRMASS WILL BE IN PLACE WHICH
WILL MINIMIZE COVERAGE OF SHOWERS AND STORMS. THE FOCUS FOR ACTIVITY
WILL BE ACROSS THE NORTHERN ZONES ONCE AGAIN ON THE LEADING EDGE OF
ANOTHER BACKDOOR COLD FRONT MOVING WITH THE UPPER WAVE. A FEW STORMS
COULD BECOME STRONG IN THIS AREA AS 30 KTS OF SHEAR IS PROGGED BY
THE NAM HERE. THE ONE LIMITING FACTOR WILL BE AVAILABLE INSTABILITY AS
MODELS DEVELOP ONLY ABOUT 500 J/KG OF CAPE BY THE AFTERNOON.
CANNOT RULE OUT A FEW WEAKER SHOWERS/STORMS DEVELOPING AND MOVING
OFF THE LARAMIE RANGE AS WELL IN THE LATE AFTERNOON BUT THESE WILL
BE WEAK AND VERY ISOLATED.

DRY ZONAL FLOW WILL THEN TAKE AHOLD OF THE FORECAST AREA FOR
TUESDAY...WITH TEMPS WARMING BACK TO MORE NORMAL VALUES FOR THIS
TIME OF YEAR. HUMIDITIES LOOK TO DROP INTO THE TEENS AND 20S FOR
MUCH OF THE AREA...WHILE  WINDS WILL CONTINUE TO BE GUSTY ALONG AND
WEST OF THE LARAMIE RANGE. WILL CONTINUE TO MONITOR TUESDAY FOR
ELEVATED FIRE WEATHER CONCERNS.

.LONG TERM...(WEDNESDAY THROUGH SATURDAY)
ISSUED AT 345 PM MDT SUN AUG 31 2014

WEDNESDAY WILL BE THE WARMEST DAY OF THE EXTENDED PERIOD WITH
SOUTHWESTERLY FLOW ALOFT AND A LEE TROUGH AT THE SFC.  700MB TEMPS
WILL RISE TO 16C WITH AROUND 30C AT 850MB.  HIGHS OVER THE PLAINS
WILL BE IN THE UPPER 80S TO LOW 90S...WHICH IS 5-10 DEGREES ABOVE
NORMAL FOR EARLY SEPTEMBER.  MAY HAVE TO DEAL WITH SOME FIRE WEATHER
CONCERNS OVER SOUTHEAST WY AS MIN RH VALUES DROP TO AROUND 15
PERCENT AND WINDS WILL BE BREEZY...ESPECIALLY TO THE WEST OF THE
LARAMIE RANGE.  UPPER LEVEL WAVE PUSHES FROM THE NORTHERN ROCKIES ON
WED TOWARD NORTH DAKOTA ON THURS.  THIS WILL PUSH A COLD FRONT
THROUGH THE CWA ON THURS MORNING WITH 10-15 DEGREES OF COOLING.  IT
IS GENERALLY A DRY FRONTAL PASSAGE...AT LEAST INITIALLY.  BY THURS
NIGHT INTO FRI THIS COULD CHANGE AS ISENTROPIC LIFT COMBINES WITH
IMPROVING JET DYNAMICS SUCH THAT SCATTERED SHOWERS DEVELOP OVER
PORTIONS OF THE CWA.  THE ECMWF HAS WIDESPREAD SHOWERS ON THURS
NIGHT WHEREAS THE GFS HAS THIS AREA FURTHER SOUTH OVER NORTHERN
COLORADO.  LLVL SOUTHEASTERLY UPSLOPE WILL CONTINUE THROUGH SATURDAY
WITH WEAK SHORTWAVES MOVING ACROSS THE REGION FROM THE SOUTHWEST.
SEEMS LIKE A FAVORABLE PATTERN FOR AT LEAST ISOLATED TO SCATTERED
SHOWERS AT TIMES ALONG WITH INCREASED CLOUD COVER AND GENERALLY HAVE
SLIGHT CHANCE POPS ON FRI AND SAT.  INSTABILITY IS QUITE LIMITED
THROUGH FRI...THEN IMPROVES SOME BY SAT (CAPE VALUES INCREASE TO
500-750 J/KG).

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z MONDAY MORNING)
ISSUED AT 1146 AM MDT SUN AUG 31 2014

SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS WILL BE POSSIBLE
THROUGH THE AFTERNOON. MUCH OF THE ACTIVITY WILL SHIFT EASTWARD
OUT OF SOUTHEAST WY BY LATE AFTERNOON. MODERATE RAIN WILL
ACCOMPANY SOME OF THE STRONGER SHOWERS...WITH BRIEF MVFR VIS
POSSIBLE. WEST TO NORTHWEST WINDS WILL BE BREEZY THROUGH 00Z OVER
MUCH OF SOUTHEAST WY WITH GUSTS TO 30 KTS.

&&

.FIRE WEATHER...
ISSUED AT 345 PM MDT SUN AUG 31 2014

SCATTERED SHOWERS AND T-STORMS WILL CONTINUE OVER THE DISTRICT
THROUGH EARLY THIS EVENING BEFORE COMING TO AN END TONIGHT. LIGHT
TO MODERATE RAIN...GUSTY DOWNDRAFT WINDS...AND OCCASIONAL
LIGHTNING WILL ACCOMPANY THE STORMS. A WEAK DISTURBANCE MOVING
OVERHEAD ON MONDAY WILL BRING A CHANCE FOR MORE ISOLATED SHOWERS
AND STORMS MAINLY OVER NORTHERN AND EASTERN PORTIONS OF THE
DISTRICT IN THE AFTERNOON. LIGHT RAINFALL AND GUSTY WINDS WILL
REMAIN A POSSIBILITY WITH THIS ACTIVITY. A MUCH DRIER AIRMASS WILL
MOVE OVERHEAD TUESDAY AND WILL REMAIN IN PLACE THROUGH WEDNESDAY.
TEMPERATURES WILL WARM BACK TO ABOVE NORMAL READINGS BY
WEDNESDAY AS WELL...WHILE WEST TO SOUTHWEST WINDS WILL REMAIN
GUSTY IN AREAS ALONG AND WEST OF THE LARAMIE RANGE.

&&

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

$$

SHORT TERM...RJM
LONG TERM...FINCH
AVIATION...FINCH
FIRE WEATHER...RJM






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