986  
FXUS65 KCYS 220311  
AFDCYS  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE CHEYENNE WY  
911 PM MDT THU AUG 21 2014  
   
UPDATE
 
 
ISSUED AT 911 PM MDT THU AUG 21 2014  
 
SHOWERS AND THUNDERSTORMS ARE STARTING TO WIND DOWN ACROSS THE  
AREA THIS EVENING. A FEW WILL LINGER THROUGH THE EVENING HOURS  
WITH MOST ACTIVITY ENDING BY MIDNIGHT. ISOLATED ACTIVITY COULD  
OCCUR LATE TONIGHT WITH A BIT OF ELEVATED INSTABILITY AND WARM  
ADVECTION. FORECAST LOOKS IN GOOD SHAPE SO NO MAJOR UPDATE AT THIS  
TIME.  
 

 
   
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.  
 

 
 

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