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[Printable]
658
FXUS65 KCYS 212341
AFDCYS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
541 PM MDT THU AUG 21 2014

.SHORT TERM...(THIS EVENING THROUGH SATURDAY NIGHT)
ISSUED AT 300 PM MDT THU AUG 21 2014

CURRENT KCYS RADAR LOOP SHOWS A FEW SHOWERS ACROSS THE AREA AND NO
THUNDERSTORMS AT THIS TIME...WHICH WAS EXPECTED DUE TO INCREASED
SUBSIDENCE ALOFT. IN ADDITION...HIGH CLOUDS ARE MOVING NORTHWARD
NEAR THE COLORADO BORDER WHICH WILL SUPPRESS CONVECTION EVEN MORE.
KEPT POP NEAR OR BELOW 20 PERCENT FOR ISOLATED SHOWERS AND SOME
ISOLATED THUNDER AT TIMES. LOWERED POP TO AROUND 10 PERCENT IN THE
LOWER VALLEYS INTO THIS EVENING. EXPECT MOST OF THE THUNDERSTORM
ACTIVITY TO BE FURTHER NORTH AS A COOL FRONT DRIFTS SOUTHWARD AND
STALLS ACROSS CENTRAL WYOMING.

MODELS CONTINUE TO SHOW A CHANGE IN THE OVERALL PATTERN ACROSS THE
ROCKY MOUNTAIN REGION FOR FRIDAY AND THIS WEEKEND. ALL MODELS
INDICATE A PRETTY STRONG COLD FRONT FOR THIS TIME OF THE YEAR
PUSHING SOUTHWARD INTO SOUTHEAST WYOMING. THIS FRONT WILL STALL
SOMETIME ON FRIDAY AS A WAVE OF LOW PRESSURE DEVELOPS ALONG THE
FRONT...AND WILL BE THE MAIN FOCUS FOR SCATTERED TO NUMEROUS SHOWERS
AND TSTORMS AS AN UPPER LEVEL TROUGH FROM WESTERN CANADA MOVE
SOUTH AND EVENTUALLY EASTWARD INTO IDAHO. THE MAIN FORECAST
CONCERN FOR FRIDAY AND FRIDAY NIGHT IS THE POTENTIAL FOR A STEADY
HEAVY RAINFALL AS AN UPPER LEVEL TROUGH NEAR THE SOUTHERN CALIF
COASTLINE EJECTS NORTHEASTWARD ACROSS THE AREA. THE ECMWF AND NAM
ARE THE MOST AGGRESSIVE WITH THE FEATURE SHOWING WIDESPREAD
SHOWERS AND NUMEROUS TSTORMS DEVELOPING ACROSS COLORADO AND
QUICKLY MOVING NORTHWARD INTO THE FORECAST AREA. THE GFS IS THE
LEAST AGGRESSIVE AND SHOWS THE TROUGH MUCH WEAKER AS IT LIFT
NORTHEAST...AND IS BARELY NOTICEABLE BY LATE FRIDAY ACROSS THE
PLAINS. INCREASED POP UP TO 65 PERCENT ACROSS THE HIGH
PLAINS...MOSTLY OVER FAR EASTERN WYOMING AND WESTERN NEBRASKA.
RAIN SHOWERS AND EVEN ISOLATED TSTORMS MAY CONTINUE WELL INTO THE
OVERNIGHT HOURS INTO EARLY SATURDAY MORNING.

FOR SATURDAY...MODELS SHOW A BRIEF BREAK IN THE ACTION BY MID TO
LATE MORNING AS REMNANT SHOWER ACTIVITY MOVES INTO THE DAKOTAS.
SHOWER AND TSTORMS WILL QUICKLY REDEVELOP FURTHER WEST ACROSS
WYOMING/UTAH AND NORTHWEST COLORADO AS THE MAIN COLD FRONT AND
PRETTY STRONG UPPER LEVEL TROUGH MOVES EASTWARD FROM IDAHO INTO
WYOMING. EXPECT ANOTHER ROUND OF SHOWERS AND TSTORMS AHEAD AND
ALONG THIS FRONT...WHICH SOME DECENT RAINFALL AMOUNTS POSSIBLE.
INCREASED POP BETWEEN 40 TO 60 PERCENT ACROSS MOST AREAS SATURDAY
AFTERNOON AND EVENING. CLEARING SKIES ARE EXPECTED AFTER MIDNIGHT
ACROSS SOUTHEAST WYOMING WITH MUCH COOLER TEMPERATURES. A FEW
SHELTERED VALLEYS MAY LOWER INTO THE 30S SATURDAY NIGHT WITH
NEAR FREEZING TEMPERATURES IN THE MOUNTAINS.

.LONG TERM...(SUNDAY THROUGH THURSDAY)
ISSUED AT 330 PM MDT THU AUG 21 2014

MODELS VERY SIMILAR ON MOVEMENT OF UPPER LOW INTO WESTERN MONTANA
EARLY SUNDAY. SUNDAY COULD BE A PRETTY BREEZY DAY AS THE LOW
PLACEMENT IN A FAVORABLE POSITION FOR STRONG WINDS. IN FACT...THE
ECMWF 700MB WINDS ACROSS SOUTHEAST WYOMING ARE APPROACHING
40KTS...GFS A LITTLE LIGHTER WITH 30-35KTS. SHOULD NOT BE MUCH IN
THE WAY OF SHOWER ACTIVITY WITH DOWNSLOPING WINDS OFF THE LARAMIE
RANGE.

NEXT SHORTWAVE TO IMPACT THE AREA COMES IN FROM THE NORTHWEST
AROUND THAT LOW MONDAY AFTERNOON. BOTH THE GFS AND ECMWF SHOWING
MOUNTAIN SHOWERS INITIALLY. THE ECMWF IS FORECASTING A MORE
WIDESPREAD SHOWERY EVENT...THOUGH GFS DOES SHOW AN INCREASE IN
COVERAGE MONDAY NIGHT. PRETTY MUCH KEPT WHAT WE HAD GOING FOR POPS
MONDAY WITH BEST CHANCES IN THE MOUNTAINS.

DISCREPANCIES BEGIN TO INCREASE AFTER THIS SHORTWAVE AS THE ECMWF
SLOWER IN MOVING OUT THIS TROUGH. BY TUESDAY AFTERNOON...THE ECMWF
SHOWS THE UPPER TROUGH AXIS OVER EXTREME EASTERN WYOMING AND THE
GFS HAS IT ALREADY MOVING INTO CENTRAL NEBRASKA. WITH THE SLOWER
ECMWF...WE REALLY BEGIN TO SEE THE DISCREPANCIES ARISE IN 700MB
TEMPERATURES. GFS FORECASTING +4 TO +8C OVER THE CWFA WITH THE
ECMWF SHOWING +10 TO +12C. DID BEGIN TO GO LOWER ON TEMPERATURES
MORE IN LINE WITH THE GFS. UNDERCUT EXTENDED PROCEDURE GUIDANCE BY
3-4 DEGREES TO COME MORE IN LINE WITH THE GFS/MEX GUIDANCE.
LOOKS FAIRY DRY WEDNESDAY AFTERNOON AND INTO THURSDAY WITH THE
TROUGH MOVING OFF TO THE EAST.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z FRIDAY AFTERNOON)
ISSUED AT 535 PM MDT THU AUG 21 2014

VFR CONDITIONS SHOULD BE THE RULE FOR ALL TERMINALS THROUGH MOST
OF THE TAF PERIOD. ISOLATED TO SCATTERED SHOWERS AND TSTMS WILL
PERSIST THROUGH MID EVE ACROSS SOUTHEAST WY AND THE WESTERN NE
PANHANDLE. MAINTAINED VCTS AT KRWL...KCYS AND KBFF AS THESE ARE
THE MOST LIKELY AREAS TO SEE CONVECTION THROUGH 03Z FRI. BRIEF
MVFR VSBYS AND GUSTY WINDS MAY ACCOMPANY SOME STORMS. OTHERWISE
SKIES WILL REMAIN BKN-TO-OVC ABOVE 10K FEET AGL. FRI AFTN WILL
FEATURE LOWERING CLOUD BASES AND ANOTHER ROUND OF SHOWERS AND
TSTMS. SOME STORMS COULD BE STRONG.

&&

.FIRE WEATHER...
ISSUED AT 205 PM MDT THU AUG 21 2014

MINIMAL FIRE WEATHER CONCERNS THROUGH EARLY NEXT WEEK.
SUBTROPICAL MOISTURE WILL REMAIN OVER THE AREA THROUGH THE WEEKEND
WITH SHOWERS AND THUNDERSTORMS POSSIBLE EACH DAY ACROSS SOUTHEAST
WYOMING AND WESTERN NEBRASKA. THERE IS A GOOD CHANCE OF WETTING
RAINS ON FRIDAY THROUGH THIS WEEKEND AS SHOWERS AND THUNDERSTORM
COVERAGE WILL BE HIGHER. TEMPERATURES WILL TREND COOLER INTO THIS
WEEKEND AS A STRONG COLD FRONT FOR THIS TIME OF THE YEAR MOVES
INTO THE REGION LATE ON SATURDAY. THIS UNSETTLED WEATHER IS
EXPECTED TO CONTINUE INTO EARLY NEXT WEEK.

&&

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

$$

SHORT TERM...TJT
LONG TERM...CLAYCOMB
AVIATION...HAMMER
FIRE WEATHER...TJT







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