Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 272213
AFDCYS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
413 PM MDT WED AUG 27 2014

.SHORT TERM...(THIS EVENING THROUGH THURSDAY)
ISSUED AT 413 PM MDT WED AUG 27 2014

THE STRONG UPPER LOW IS MOVING INTO WESTERN COLORADO THIS
AFTERNOON AS SEEN ON WATER VAPOR IMAGERY. A POTENT SHORTWAVE
MOVED OUT AHEAD OF THE LOW AND OVER THE FORECAST AREA THIS
MORNING...SPARKING OFF NUMEROUS SHOWERS AND TSTORMS MAINLY ALONG
AND EAST OF THE LARAMIE RANGE. SOME TRAINING OF STORMS WAS OBSERVED
ALONG A SFC BOUNDARY THAT WAS SITUATED NEAR THE WY/NE BORDER
EARLIER...WITH MODERATE TO HEAVY RAIN OBSERVED WITH THE
THUNDERSTORM ACTIVITY. SOME MINOR TO MODERATE FLOODING OCCURRED
ACROSS CENTRAL GOSHEN COUNTY WITHIN THE AREA OF TRAINING STORMS.
THAT BOUNDARY HAS SINCE PUSHED OFF TO THE SOUTH AND EAST...LIKELY
WITH THE HELP OF THUNDERSTORM OUTFLOW AND AS SFC CYCLOGENESIS IS
OCCURRING IN SOUTHEAST COLORADO...ACCELERATING THE SOUTHWARD
MOVEMENT OF THE BOUNDARY. THE BULK OF THE THUNDERSTORM ACTIVITY IS
NOW OVER FAR NORTHERN AND EASTERN PORTIONS OF THE PANHANDLE THIS
AFTERNOON ON THE LEADING EDGE OF THE SHORTWAVE...WITH THE HEAVIEST
RAIN EXPECTED TO PUSH OFF TO THE EAST-NORTHEAST THROUGH THE
EVENING. ANOTHER ROUND OF SHOWERS AND STORMS ARE MOVING UP FROM
THE SOUTHWEST ON THE NOSE OF A JETLET ROUNDING THE BASE OF THE
TROUGH. THIS ACTIVITY IS OCCURRING WITHIN A DRIER AIRMASS PER
WATER VAPOR IMAGERY...SO RAIN RATES SHOULD BE LESS OVERALL.
INCREASING SOLAR INSOLATION OVER THE NEXT FEW HOURS COULD HELP
DESTABILIZE THE ATMOSPHERE SOMEWHAT ACROSS THE WYO PLAINS...SO
CANNOT RULE OUT THE IDEA THAT THESE STORMS MOVING OFF THE MOUNTAINS
COULD BECOME STRONG WITH THE HELP OF THE APPROACHING JET. HOWEVER THE
ATMOSPHERE IS FAIRLY WORKED OVER FROM EARLIER ACTIVITY SO NOT
WHOLLY CONFIDENT STORMS WILL INTENSIFY MUCH.

THE UPPER LOW WILL CONTINUE TO TREK SOUTHEAST INTO THE CENTRAL
PLAINS THROUGH THURSDAY...WITH WRAPAROUND ENERGY AND MOISTURE
MAINTAINING CHANCES FOR SHOWERS AND TSTORMS ACROSS THE CWA TONIGHT.
MIDLEVEL CONVERGENCE WITHIN THE TROUGH AXIS WILL MOVE OVERHEAD ON
THURSDAY...WITH THE ADDITION OF BROADSCALE LIFT WITHIN THE LEFT
ENTRANCE OF THE CURVED JET AIDING IN DEVELOPMENT OF CONVECTION
THROUGH THE DAY. THE MAIN FOCUS WILL BE SOUTH OF A RAWLINS-LUSK-
CHADRON LINE. MUCH DRIER AIR WILL FILTER IN FROM THE NORTHWEST AS
A SHORTWAVE RIDGE MOVES OVERHEAD THURSDAY NIGHT AND EARLY
FRIDAY...WITH A WEAK WAVE APPROACHING FROM THE NORTHWEST FRIDAY
AFTERNOON. A FEW WEAK TSTORMS ARE POSSIBLE IN THE AFTERNOON AS THE
WAVE APPROACHES.

.LONG TERM...(THURSDAY NIGHT THROUGH WEDNESDAY)
ISSUED AT 413 PM MDT WED AUG 27 2014

MEDIUM RANGE MODELS ARE IN EXCELLENT AGREEMENT WITH A BROAD MIDLVL
SHORTWAVE MOVING ACROSS THE PACIFIC NW EARLY IN THE PERIOD. SEASONAL
WARMTH WILL OCCUR IN ADVANCE OF THIS FEATURE WITH H7 TEMPS AROUND 10
TO 14 C PER THE GFS ON SAT. CONSIDERABLE 700-300 MILLIBAR MOISTURE
AND INCREASING QG ASCENT WITH THE APPROACHING WAVE WOULD SUGGEST AN
INCREASE IN SHOWER AND TSTM ACTIVITY...EVEN AT NON DIURNALLY FAVORED
TIMES OF DAY. DO NOT EXPECT A WASHOUT BY ANY MEANS...BUT THERE WILL
PROBABLY BE CONVECTION AROUND. LOOKING A BIT BREEZY EACH AFTN OVER
THE HOLIDAY WEEKEND...ESPECIALLY WEST OF THE LARAMIE RANGE WITH AN
INCREASE IN HEIGHT GRADIENTS ALOFT AND THE SFC LOW PASSING ACROSS
NORTHERN WY. COOLER ON SUN/MON AS THE UPPER-LEVEL SYSTEM MOVES
OVERHEAD. THE ECMWF SHOWS 1000-500 MILLIBAR THICKNESSES FALLING TO
AROUND 570 DM...AND MOS GUIDANCE SUGGESTS SFC TEMPS WILL BE A GOOD
10 TO 15 DEGREES COOLER WHEN COMPARED TO SAT. AN UNSETTLED WEATHER
PATTERN WILL PERSIST THRU EARLY NEXT WEEK WITH DISTURBANCES EMBEDDED
WITHIN QUASI-ZONAL FLOW. WEAK UPPER-LEVEL RIDGING SHOULD GIVE WAY TO
A GRADUAL WARMING TREND THROUGH MIDWEEK WITH LESSER CHANCES FOR PCPN
FROM TUE ONWARD.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z THURSDAY MORNING)
ISSUED AT 1130 AM MDT WED AUG 27 2014

SCATTERED TO NUMEROUS SHOWERS AND STORMS CAN BE EXPECTED ACROSS
SOUTHEAST WY AND THE WESTERN NE PANHANDLE TODAY. MOST TERMINALS
WILL SEE LOWER CIGS BETWEEN 5K AND 8K FEET AGL THROUGH THE TAF
PERIOD...WITH OCCASIONAL MVFR CONDITIONS WITH BKN-TO-OVC SKIES
AROUND 2K FEET. LOWEST CIGS/VSBYS WILL OCCUR BENEATH SHOWERS AND
STORMS. A FEW STRONGER STORMS ARE POSSIBLE THIS AFTN FOR THE NE
PANHANDLE SITES...WITH TORRENTIAL DOWNPOURS AND STRONG/VARIABLE
WINDS POSSIBLE ALONG WITH SMALL HAIL. SHOWER ACTIVITY IS LIKELY
TO PERSIST ACROSS MUCH OF THE REGION OVERNIGHT. WE CANNOT RULE
OUT MVFR CIGS LATE TONIGHT OR EARLY THU...ESPECIALLY IN AREAS
WHICH RECEIVE HEAVIER RAINFALL THIS AFTN.

&&

.FIRE WEATHER...
ISSUED AT 413 PM MDT WED AUG 27 2014

NUMEROUS SHOWERS AND SCATTERED THUNDERSTORMS WILL
CONTINUE OVER THE DISTRICT THIS AFTERNOON AND TONIGHT. THIS
ACTIVITY WILL PRODUCE MODERATE TO HEAVY RAIN AND PERHAPS SOME
SMALL HAIL AS WELL. A MORE ISOLATED COVERAGE FOR SHOWERS AND
T-STORMS IS EXPECTED FOR THURSDAY...WITH THE MAIN FOCUS FOR THIS
ACTIVITY IN THE MOUNTAINS AND NEAR THE COLORADO BORDER. DRIER AND
WARMER WEATHER WILL RETURN FRIDAY AND CONTINUE THIS
WEEKEND...ALONG WITH GUSTY WEST TO SOUTHWEST WINDS. THERE WILL BE
A SLIGHT CHANCE FOR SHOWERS AND THUNDERSTORMS LATE SUNDAY AND LABOR
DAY WITH THE PASSAGE OF A UPPER LEVEL TROUGH AND PACIFIC COLD
FRONT.

&&

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

$$

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






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