085  
FXUS65 KCYS 280509  
AFDCYS  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE CHEYENNE WY  
1009 PM MST THU NOV 27 2014  
   
SHORT TERM
 
(TONIGHT THROUGH SATURDAY)  
ISSUED AT 322 PM MST THU NOV 27 2014  
 
WARM AND WINDY CONDITIONS CONTINUE ACROSS THE CWA THIS AFTN. A HIGH  
WIND WARNING WILL REMAIN IN EFFECT FOR ARL AND BRX THROUGH 5 PM THIS  
EVE AS RECENT HIGHWAY OBS HAVE SHOWN SUST WINDS AROUND 35-40 MPH AND  
GUSTS NEAR 55 MPH. UNTIL RECENTLY HOWEVER...THE TYPICAL WINDY AREAS  
HAVE STRUGGLED TO GUST MUCH HIGHER THAN 50 MPH. BELIEVE THIS IS THE  
RESULT OF EXTENSIVE MIDLVL CLOUD COVER PREVENTING THE EROSION OF AN  
IMPRESSIVE SFC INVERSION...KEEPING THE STRONGEST FLOW JUST OFF THE  
SURFACE. WOULD NOT TAKE MUCH TO ACHIEVE WARNING CRITERIA AS THE CYS  
VAD WIND PROFILE SHOWED 50-55 KTS OF FLOW ONLY AROUND 2K FEET AGL AT  
18Z TODAY. DECIDED TO CANCEL THE WARNING FOR THE SUMMIT AND ADJACENT  
SOUTH LARAMIE RANGE FOOTHILLS AS VEDAUWOO HAS BEEN BELOW 45 MPH ALL  
DAY. THE SFC PRESSURE GRADIENT WILL REMAIN STRONG OVERNIGHT SO GUSTY  
WINDS SHOULD PERSIST. HOWEVER THE H85 CAG-CPR GRADIENT IS PROGGED TO  
FALL BELOW 55 METERS SHORTLY AFTER 00Z SO EXPECT ANY POTENTIAL FOR  
60 MPH GUSTS TO QUICKLY DIMINISH AFTER SUNSET.  
 
ANOTHER DAY OF STRONG WESTERLY/DOWNSLOPING WINDS FOR FRIDAY AS THE  
LEE SFC TROUGH REMAINS TO THE EAST OF THE CWA. LITTLE CHANGE IN THE  
OVERALL SYNOPTIC PATTERN WITH BOTH THE GFS AND NAM SHOWING A 130 KT  
H25 JET STREAK ENTERING NORTHERN WY AT 12Z FRI. STRONG SUBSIDENCE IS  
EXPECTED IN THE FAVORED RIGHT EXIT REGION AND WINDS ALOFT COULD BE  
MUCH HIGHER THAN TODAY PER RECENT MODEL PROGS. 60 TO 70 METER CAG-  
CPR GRADIENTS DEVELOPING AFTER 12Z FRI ARE CONCERNING...ESPECIALLY  
SEEING GFS/NAM H75 FLOW AS HIGH AS 60 KTS ALONG THE LARAMIE RANGE BY  
EARLY AFTN. MUCH LIKE TODAY...GFS AND NAM VERTICAL XSECTIONS SHOW A  
HEALTHY 50 TO 60 KT BELT OF FLOW JUST OFF THE SFC ON FRI AFTN. GAVE  
STRONG CONSIDERATION TO A HIGH WIND WATCH AFTER 18Z BUT DECIDED  
AGAINST IT. NAM SOUNDINGS CONTINUE TO SHOW A STRONG SFC INVERSION  
WHICH WAS OBVIOUSLY A MAJOR CONTRIBUTING FACTOR IN THE LIMITED WINDS  
TODAY. WAVE CLOUDS WILL ALSO BE AROUND...ALTHOUGH AS A GENERAL RULE  
CLOUD COVER SHOULD BE LESS. CHANCES OF HITTING HIGH WIND CRITERIA  
ARE PROBABLY HIGHER TOMORROW...BUT POOR LAPSE RATES COULD KEEP WINDS  
VERY MARGINAL AT BEST. HIGH WIND POTENTIAL HAS BEEN WELL ADVERTISED  
THROUGH THE END OF THE WEEK...SO THE PREFERRED COURSE OF ACTION IS  
TO LET THE NEXT COUPLE OF SHIFTS MONITOR TRENDS.  
 
ASIDE FROM THE WINDS...FRIDAY SHOULD BE QUITE WARM ALONG AND EAST OF  
THE LARAMIE RANGE. GFS/ECMWF H7 TEMPERATURES ARE IN THE 3 TO 5 DEG C  
RANGE IN A FAVORABLE SYNOPTIC PATTERN FOR DOWNSLOPE OR COMPRESSIONAL  
WARMING. MOS GUIDANCE SUGGESTS LOW TO MID 60S FOR MOST OF SOUTHEAST  
WY AND THE WESTERN NE PANHANDLE...SO CONTINUED TO TREND WARMER WITH  
THE ANTICIPATION THAT CLOUD COVER WILL NOT BE QUITE AS THICK DURING  
PEAK HEATING GIVEN RH PROGS THROUGH THE COLUMN. THERMAL PROFILES ARE  
EXPECTED TO COOL SLIGHTLY ON SAT AHEAD OF A STRONG COLD FRONT MOVING  
SOUTH ACROSS THE NORTHERN ROCKIES AND HIGH PLAINS. PRESSURE FALLS IN  
ADVANCE OF THIS FEATURE WILL ONCE AGAIN STRENGTHEN LLVL GRADIENTS IN  
THE GAP AREAS. CONTINUED SUBSIDENCE AND IMPROVEMENT IN LAPSE RATES  
WOULD SUGGEST POTENTIAL FOR HIGH WINDS ON SAT AFTN AS WELL.  
   
LONG TERM
 
(SATURDAY NIGHT THROUGH THURSDAY)  
ISSUED AT 322 PM MST THU NOV 27 2014  
 
A SHORTWAVE TROUGH WILL MOVE EAST ACROSS THE PAC NW AND NORTHERN  
ROCKIES SATURDAY NIGHT...AND ACROSS THE NORTHERN PLAINS THROUGH  
SUNDAY. THE COLD FRONT ASSOCIATED WITH THIS TROUGH WILL SLIDE SOUTH  
ACROSS THE HIGH PLAINS AND INTO THE CWA ON SATURDAY NIGHT...AND  
LOOKS TO STALL JUST WEST OF THE LARAMIE RANGE THRU SUNDAY. BEST  
MIDLEVEL FORCING WITH THE WAVE WILL REMAIN NORTH OF THE CWA...WHILE  
JET DYNAMICS WILL BE BEST IN COLORADO AND THE CENTRAL PLAINS.  
THEREFORE...PRECIP CHANCES FOR THE CWA WILL BE TIED TO FRONTAL  
FORCING IN ADDITION TO OROGRAPHICS AS THE FRONT SLIDES WEST OF THE  
LARAMIE RANGE AND SFC WINDS TURN NNE. EXPECT TO SEE RAIN/SNOW MIX AT  
THE ONSET LATE SATURDAY NIGHT IN THE FAR NORTHERN ZONES BUT WILL  
QUICKLY CHANGE TO ALL SNOW AS THE FRONT RUSHES SOUTH AND COLD  
CANADIAN AIR FILTERS IN. SHOULD SEE LIGHT SNOW SPREAD NORTH TO SOUTH  
ACROSS THE CWA THROUGH SUNDAY AFTERNOON...WITH THE FOCUS SHIFTING TO  
THE MOUNTAINS AND IMMEDIATE LEESIDE PLAINS FOR THE EVENING IN  
UPSLOPE FLOW. AGAIN...WITH THE LACK OF UPPER SUPPORT...DO NOT EXPECT  
MUCH MORE THAN AN INCH OR TWO OF ACCUMULATION. WILL ALSO SEE A BRIEF  
RESPITE FROM THE WINDS AS THE FRONT LOOKS TO REMAIN STALLED OVER THE  
MOUNTAINS THROUGH SUNDAY NIGHT. BROADSCALE RIDGING WILL TAKE HOLD  
OVER THE ROCKIES THROUGH THE REMAINDER OF THE PERIOD WITH THE  
LEESIDE SFC TROUGH DEVELOPING ONCE AGAIN LATE MONDAY. THE FRONT  
SHOULD KICK EASTWARD SLOWLY BUT SURELY AS THE LEE TROUGH DEVELOPS.  
WINDS WILL PICK UP ON MONDAY AS THE FRONT SHIFTS EAST AND  
STRENGTHENS THE SW-NE PRESSURE GRADIENT ALONG AND EAST OF THE  
LARAMIE RANGE THROUGH TUESDAY MORNING.  
 
TUESDAY WILL BE MILD AND BREEZY WITH DRY CONDITIONS. MODELS THEN  
DIFFER WITH THE SYNOPTIC PATTERN WEDNESDAY WITH THE GFS BRINGING A  
SHORTWAVE TROUGH ACROSS THE ROCKIES WHILE THE ECMWF/CANADIAN MODELS  
MAINTAIN RIDGING ALOFT. TRENDED THE FORECAST TOWARD THE LATTER TWO  
MODELS...ALTHOUGH DID NOT COMPLETELY DISCOUNT THE GFS AS THE  
ENSEMBLE MEAN HINTS AT THE TROUGH MOVING OVERHEAD AS WELL. KEPT  
SLIGHT CHANCE POPS MAINLY IN THE WEST...WITH HIGHER POPS IN THE  
MOUNTAINS THROUGH WEDNESDAY NIGHT TO ACCOUNT FOR THIS UNCERTAINTY.  
TEMPS WILL REMAIN MILD FOR WEDNESDAY WITH BREEZY WINDS OUT WEST.  
 

 
   
AVIATION
 
(FOR THE 06Z TAFS THROUGH 06Z FRIDAY NIGHT)  
ISSUED AT 1006 PM MST THU NOV 27 2014  
 
VFR THROUGH NEXT 24 HOURS...BUT HAVE STRONG WINDS TO DEAL WITH FOR  
OUR SOUTHEAST WYOMING AIRPORTS. MODERATE OR GREATER TURBULENCE ON  
LANDINGS AND TAKEOFFS AS WIND SPEEDS OFF THE SURFACE CLOSE TO  
60KTS FRIDAY. SHOULD SEE LOTS OF MOUNTAIN WAVE TURBULENCE OFF THE  
LARAMIE RANGE...ESPECIALLY DURING THE DAYLIGHT HOURS.  
 

 
   
FIRE WEATHER
 
 
ISSUED AT 250 AM MST THU NOV 27 2014  
 
MINIMAL FIRE WEATHER CONCERNS THROUGH THE HOLIDAY WEEKEND. TEMPERATURES  
WILL BE QUITE MILD OVER THE NEXT FEW DAYS. MINIMUM AFTERNOON HUMIDITY  
VALUES WILL BE LOWEST ON FRIDAY AND SATURDAY WITH A FEW LOCATIONS TO  
THE EAST OF THE LARAMIE RANGE IN THE 15-20 PERCENT RANGE. IT WILL BE  
WINDY ACROSS SOUTHEAST WYOMING THROUGH SATURDAY WITH GUSTS TO 35-40  
MPH COMMON...ESPECIALLY DURING THE AFTERNOONS.  
 

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

 
 

 
 
SHORT TERM...CLH  
LONG TERM...RJM  
AVIATION...GCC  
FIRE WEATHER...CLH/ZF  
 
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