923  
FXUS65 KCYS 181150  
AFDCYS  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE CHEYENNE WY  
448 AM MST WED DEC 18 2024  
   
KEY MESSAGES  
 
- A FAIRLY WIDESPREAD HIGH WIND EVENT WILL OCCUR TODAY AND  
TONIGHT FOR THE SOUTHEAST WYOMING WIND PRONE LOCATIONS AND  
NEARBY LOWER ELEVATIONS. HIGH WIND WARNINGS WILL CONTINUE FOR  
THE WIND PRONE LOCATIONS AND WILL BEGIN AT 3 PM THIS AFTERNOON  
FOR NEARBY LOWER ELEVATIONS. HIGH WIND WARNINGS WILL CONTINUE  
UNTIL 5 AM THURSDAY.  
 
- IT WILL STILL BE WINDY DURING THE DAYTIME ON THURSDAY, THOUGH  
WINDS WILL REMAIN BELOW HIGH WIND CRITERIA.  
 
- DRY AND MILD WEATHER WILL CONTINUE FOR FRIDAY THROUGH THE WEEKEND.  
 
 
   
SHORT TERM /THROUGH THURSDAY NIGHT/  
 
ISSUED AT 205 AM MST WED DEC 18 2024  
 
TODAY...NORTHWEST FLOW ALOFT STRENGTHENS EVEN FURTHER WITH THE CRAIG-  
CASPER 850/700 MB HEIGHT DIFFERENCES INCREASING TO 88/73 METERS BY  
00Z AND 700 MB WINDS 55 TO 65 KNOTS WITH LOCAL HIGH WIND MODELS  
SUGGESTING WINDS EXCEEDING HIGH WIND CRITERIA FOR OUR WIND PRONE  
LOCATIONS, AND LIKELY NEARBY LOWER ELEVATION LOCATIONS. WITH DECENT  
DOWNWARD MOTION, WE BELIEVE EVEN OUR LOWER ELEVATIONS OF SOUTHEAST  
WYOMING WILL LIKELY EXCEED HIGH WIND CRITERIA, THUS WE HAVE INCLUDED  
RAWLINS, LARAMIE, CHEYENNE, WHEATLAND AND DOUGLAS IN THE HIGH WIND  
WARNING STARTING FOR THESE LOCATIONS AT 3 PM. MAXIMUM TEMPERATURES  
WILL BE WARMER THAN YESTERDAY WITH 700 MB TEMPERATURES NEAR 3  
CELSIUS.  
 
TONIGHT...LOW AND MID LEVEL GRADIENTS REMAIN STRONG ALTHOUGH CRAIG  
TO CASPER 850/700 MB HEIGHT DIFFERENCES SLOWLY DECREASE TO 66/61 METERS  
BY 12Z, THUS THE HIGH WIND WARNING CONTINUES FOR OUR WIND PRONE  
LOCATIONS, AND NEARBY LOWER ELEVATIONS. NOT AS COLD AS THE PREVIOUS  
NIGHT DUE TO EXPECTED WINDS AND A MODERATING AIRMASS.  
 
THURSDAY...NORTHWEST FLOW ALOFT WEAKENS SLIGHTLY, AND WITH LOW AND  
MID LEVEL GRADIENTS WEAKENING, WINDS LOOK TO REMAIN BELOW HIGH WIND  
CRITERIA, THOUGH IT WILL STILL BE WINDY. A FAST MOVING SHORTWAVE  
TROUGH ALOFT WILL SWEEP ACROSS THE CENTRAL PLAINS STATES, SENDING A  
COLD FRONT ACROSS OUR NORTHERN COUNTIES AND PRODUCING A COOLER DAY  
COMPARED TO TODAY, WITH 700 MB TEMPERATURES NEAR -4 CELSIUS.  
 
THURSDAY NIGHT...A COLDER AIRMASS MOVES OVERHEAD IN THE WAKE OF THE  
COLD FRONT, AND WITH MOSTLY CLEAR SKIES AND LESS WIND, MINIMUM  
TEMPERATURES WILL BE COLDER THAN THE PREVIOUS NIGHT. NORTHWEST FLOW  
ALOFT WEAKENS SOMEWHAT.  
 
 
   
LONG TERM /FRIDAY THROUGH TUESDAY/  
 
ISSUED AT 205 AM MST WED DEC 18 2024  
 
MEDIUM TO LONG RANGE MODELS IN VERY GOOD AGREEMENT THIS WEEKEND  
THROUGH EARLY NEXT WEEK WITH RELATIVELY SMALL ENSEMBLE SPREADS  
FOR MOST DAYS. MODELS SHOW AN UPPER LEVEL RIDGE AXIS PUSHING  
INTO THE INTERMOUNTAIN WEST AND THE FRONT RANGE THIS WEEKEND,  
RESULTING IN TEMPERATURES WELL ABOVE NORMAL FOR THIS TIME OF THE  
YEAR. THE WEATHER WILL REMAIN DRY FRIDAY THROUGH MOST OF  
SUNDAY, BUT PERIODS OF WINDY CONDITIONS AND THE POTENTIAL FOR  
STRONG WINDS EXPECTED FRIDAY MORNING WITH A BETTER CHANCE ON  
SUNDAY. 700MB WINDS ARE MARGINAL FRIDAY MORNING THROUGH THE  
AFTERNOON HOURS WITH LIMITED LOW LEVEL SUBSIDENCE CENTERED OVER  
A SMALL AREA TO THE LEE OF THE SNOWY RANGE AND SOUTHERN LARAMIE  
RANGE. EXPECT ELEVATED WINDS DURING FRIDAY, BUT NOT EXPECTED  
HIGH WIND CRITERIA AT THIS TIME. SUNDAY LOOKS MORE IMPRESSIVE  
FOR STRONG WINDS, ESPECIALLY ACROSS SOUTHEAST WYOMING. MODELS  
SHOW A FAST MOVING, BUT POTENT, PACIFIC SHORTWAVE EJECTING  
EASTWARD ACROSS IDAHO AND NORTHERN WYOMING SUNDAY. MOST MODELS  
SHOW 700MB WINDS INCREASING TO 50 TO 65 KNOTS AT THE BASE OF  
THIS SHORTWAVE WITH A STRONG 110 KT JET MOVING ACROSS SOUTHEAST  
WYOMING DURING THE DAY. LOW LEVEL 700MB SUBSIDENCE IS PLENTIFUL  
WITH VALUES SIMILAR TO TODAY'S (WEDNESDAY/WEDNESDAY NIGHT)  
EVENT. INCREASED WINDS TO HIGH WIND CRITERIA FOR MOST OF SUNDAY  
AND INTO SUNDAY EVENING. WIND PRONE AREAS LOOK LIKE A GOOD BET  
WITH STRONG WINDS POSSIBLE EVEN IN THE SUB-WIND PRONE AREAS SUCH  
AS CHEYENNE, LARAMIE VALLEY, AND EAST PLATTE COUNTY. HIGH  
TEMPERATURES WILL TREND INTO THE 50S TO LOW 60S BY THIS WEEKEND,  
WHICH IS AROUND 15 TO 20 DEGREES ABOVE NORMAL. SLIGHTLY COOLER  
TEMPERATURES EXPECTED FOR CARBON COUNTY DUE TO PERSISTENT  
TEMPERATURE INVERSIONS JUST OFF THE SURFACE.  
 
FOR EARLY NEXT WEEK AND INTO CHRISTMAS DAY, A SLIGHT PATTERN  
SHIFT IS EXPECTED BEHIND THE FAST MOVING PACIFIC SHORTWAVE. MID  
TO UPPER LEVEL FLOW IS FORECAST TO SHIFT INTO THE NORTHWEST  
WHICH SHOULD ALLOW FOR ADDITIONAL SHORTWAVE DISTURBANCES TO DIG  
SOUTH OUT OF WESTERN CANADA. OVERALL, TEMPERATURES WILL TREND  
COOLER EACH DAY...BUT SHOULD REMAIN ABOVE AVERAGE FOR THIS TIME  
OF THE YEAR. MOUNTAIN SNOWFALL IS FORECAST TO INCREASE ON MONDAY  
WELL AHEAD OF THE NEXT PACIFIC SYSTEM. WILL HAVE TO WATCH THIS  
NEXT PACIFIC STORM SYSTEM, WHICH MODELS SHOW PUSHING ONSHORE  
EARLY TUESDAY MORNING AND THEN THROUGH THE GREAT BASIN REGION  
TUESDAY NIGHT. MODELS AND ENSEMBLES ARE IN PRETTY GOOD AGREEMENT  
FOR 7 TO 8 DAYS OUT, SHOWING AN INCREASING CHANCE FOR SNOW  
ACROSS THE WHOLE AREA AS ALL DETERMINISTIC MODELS SHOW THE  
POTENTIAL FOR A CLOSED LOW DEVELOPING ACROSS THE HIGH PLAINS.  
LEE SIDE CYCLOGENESIS IS POSSIBLE IN THIS PATTERN, BUT IT IS  
UNKNOWN WHERE THIS WILL TAKE PLACE. INCREASED POP ACROSS THE  
AREA LATE TUESDAY AND INTO CHRISTMAS DAY WITH TEMPERATURES  
LOWERING CLOSER TO NEAR-NORMAL. MANY ENSEMBLE MEMBERS AGREE WITH  
THIS OVERALL TREND AS WELL SO LOWERED TEMPERATURES CLOSER TO THE  
NBM 25TH PERCENTILE.  
 
 
   
AVIATION /12Z TAFS THROUGH 12Z THURSDAY/  
 
ISSUED AT 448 AM MST WED DEC 18 2024  
 
THE NEXT PACIFIC UPPER LEVEL TROUGH IS FORECAST TO DIG SOUTH AND  
EAST TODAY AND INTO THIS EVENING. MAINLY A WIND FORECAST EXPECTED  
FOR AVIATION WITH ANY PRECIPITATION REMAINING WELL NORTH OF THE  
AREA.  
 
HAZARDS/WEATHER TRENDS: VFR CONDITIONS WILL PREVAIL THROUGH THE  
DAY AND INTO TONIGHT. ANY LINGERING FOG FROM LATE LAST NIGHT HAS  
LIFTED AND DISSIPATED. SOUTHWEST WINDS WILL INCREASE THIS MORNING  
AND WILL LIKELY BECOME STRONGER THROUGH THE AFTERNOON AND INTO THE  
EVENING HOURS AS WINDS SHIFT INTO THE WEST AND EVENTUALLY NORTHWEST  
TONIGHT. GUSTS OF 40 TO 50 KNOTS ARE POSSIBLE AT KLAR, KRWL, AND KCYS  
AFTER 20Z THIS AFTERNOON.  
 
 
   
CYS WATCHES/WARNINGS/ADVISORIES  
 
WY...HIGH WIND WARNING FROM 3 PM THIS AFTERNOON TO 5 AM MST  
THURSDAY FOR WYZ101-107-109-115-118.  
HIGH WIND WARNING UNTIL 5 AM MST THURSDAY FOR WYZ104-106-110-  
116-117.  
NE...NONE.  
 
 
 
 
 
SHORT TERM...RUBIN  
LONG TERM...TJT  
AVIATION...TJT  
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