730  
FXUS65 KCYS 182337  
AFDCYS  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE CHEYENNE WY  
437 PM 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 232 PM MST WED DEC 18 2024  
 
AFTERNOON GOES SATELLITE IMAGERY OVER SOUTHEAST WYOMING REVEALS A  
PATTERN OF MOUNTAIN WAVE CLOUDS AND SUBSIDENCE REGIONS INDICATIVE OF  
THE HIGH-WIND EVENT CURRENTLY UNDERWAY. A STRONG PRESSURE GRADIENT,  
RESULTING FROM A BROAD TROUGH OVER THE MIDWEST AND A FLAT RIDGE OVER  
THE SOUTHWEST UNDERNEATH A SHORTWAVE TROUGH, WILL CONTINUE TO  
PROVIDE THE INGREDIENTS FOR OUR HIGH WINDS TODAY. GUSTS OVER 50  
KNOTS HAVE BEEN REPORTED IN A MAJORITY OF THE FORECAST ZONES  
CURRENTLY UNDER THE WARNING, WITH GUSTS AS HIGH AS 45 KNOTS EASTWARD  
INCLUDING CHEYENNE PROPER. THIS HIGH WIND EVENT WILL CONTINUE  
THROUGHOUT THE AFTERNOON AND EVENING WITH FORECAST GUIDANCE AND  
LOCAL MACHINE LEARNING SUPPORT IN EXCELLENT AGREEMENT ON HIGH  
PROBABILITIES OF EXCEEDING 50 KNOTS. A PROGRESSIVE TROUGH WILL  
RAPIDLY MOVE EASTWARD THROUGH THE NORTHERN ROCKIES OVERNIGHT TONIGHT  
WITH A COLD FRONT DRAGGING SOUTHWARD THROUGH THE HIGH PLAINS TONIGHT  
THROUGH TOMORROW MORNING. THIS FRONTAL BOUNDARY WILL AFFECT MOST  
AREAS EAST OF I-25 IN SOUTHEAST WYOMING AS WELL AS THE NEBRASKA  
PANHANDLE, DROPPING TEMPERATURES OVERNIGHT AND RESULTING IN A COOLER  
DAY ON THURSDAY. THIS SURFACE FRONT WILL LIKELY STALL OUT SOMEWHERE  
ALONG OR JUST NORTH OF CHEYENNE AND THE I-80 CORRIDOR AS MUCH OF THE  
GENERAL MOMENTUM CONTINUES EASTWARD RATHER THAN SOUTHWARD. THUS,  
OVERNIGHT LOWS TONIGHT AND HIGH TEMPERATURES ON THURSDAY WILL REMAIN  
LARGELY UNAFFECTED BY THIS SYSTEM. IN FACT, AFTERNOON HIGHS MAY WARM  
BY A DEGREE OR TWO IN CHEYENNE ON THURSDAY, RUNNING AROUND 15  
DEGREES ABOVE AVERAGE FOR MID DECEMBER. EXPECT A GENERALLY CLEAR  
OVERNIGHT ON THURSDAY NIGHT WITH TEMPERATURES NEAR TO SLIGHTLY ABOVE  
AVERAGE. FORECAST CONFIDENCE IS EXTREMELY HIGH THROUGHOUT THE SHORT  
TERM. MINOR UPWARD ADJUSTMENTS WERE DONE TO WIND AND TEMPERATURE  
GRIDS TO IMPROVE ON MODEL BIASES.  
 

 
   
LONG TERM /FRIDAY THROUGH WEDNESDAY/
 
 
ISSUED AT 232 PM MST WED DEC 18 2024  
 
THE OVERALL WEATHER PATTERN DEPICTED BY THE MODELS  
HAVE REMAINED CONSISTENT OVER THE PAST FEW MODEL RUNS LEADING TO  
HIGH CONFIDENCE IN THE SYNOPTIC SETUP. A RIDGE WILL BEGIN TO PUSH  
INTO OUR REGION KEEPING OUR DAYTIME TEMPERATURES ABOVE AVERAGE AND  
OUR OVERNIGHT TEMPERATURES WILL BE EITHER SLIGHTLY ABOVE AVERAGE TO  
AVERAGE DEPENDING ON HOW CLOUDY THE SKIES GET TO AFFECT RADIATIONAL  
COOLING IN THE OVERNIGHT HOURS. LOOKING AT GFS OMEGA FIELDS THIS  
WEEKEND, THERE IS A SIGNAL FOR A MOUNTAIN WAVE SETUP ON SUNDAY.  
DEPENDING ON HOW STRONG (DEEP) THIS MOUNTAIN WAVE WILL BECOME WILL  
CORRELATE TO HOW STRONG THE WINDS WILL BE ESPECIALLY IN OUR WIND  
PRONE AREAS. THE UNCERTAINTY WITH THIS MOUNTAIN WAVE IS WITH THE  
MAGNITUDE. BEING A FEW DAYS OUT THE MODELS CANNOT RESOLVE THE  
COMPLETE DETAILS OF THE MOUNTAIN WAVE. WINDS LOOK TO MEET THE HIGH  
WIND CRITERIA FOR THE WIND PRONE AREAS. SUB-WIND PRONE AREAS SUCH AS  
CHEYENNE, LARAMIE VALLEY, AND EAST PLATTE COUNTY MAY ALSO REACH  
CRITERIA BUT NOT QUITE CERTAIN FOR THOSE.  
 
FOR THE HOLIDAYS, THERE IS A LOW PRESSURE SYSTEM THAT DIVES OUT OF  
BRITISH COLUMBIA AND THE PACIFIC NORTHWEST THAT MAY GIVE US SOME  
SNOW FOR THE CHRISTMAS TIME PERIOD. THE CURRENT PATH IS PROJECTED TO  
SCATHE THE NORTHEAST PORTION OF WYOMING BUT IF THE SYSTEM DIVES  
FURTHER SOUTH, THE SYSTEM COULD GIVE US SOME SNOW FOR THE HOLIDAYS.  
BEING THE HOLIDAY SEASON WITH MANY TRAVELING THIS SYSTEM WILL BE  
MONITORED CLOSELY TO SEE HOW THE MODELS FURTHER RESOLVE THE SYSTEM.  
 

 
   
AVIATION /00Z TAFS THROUGH 00Z FRIDAY/
 
 
ISSUED AT 432 PM MST WED DEC 18 2024  
 
VFR CONDITIONS EXPECTED FOR THE FORECAST PERIOD, BUT STRONG  
WINDS AND LOW LEVEL WIND SHEAR WILL STILL MAKE FOR CHALLENGING  
AVIATION CONDITIONS. OVERALL, STRONG WINDS WILL CONTINUE THROUGH  
THE NIGHT AND THURSDAY, BUT THERE MAY BE PERIODS ESPECIALLY THIS  
EVENING BETWEEN ABOUT NOW AND 05Z AND THURSDAY MORNING BETWEEN  
ABOUT 13Z AND 17Z WHEN THE WINDS DECOUPLE FROM THE SURFACE.  
WHILE SURFACE WINDS MAY BE TEMPORARILY LIGHT DURING THESE  
PERIODS, LLWS WILL STILL BE PRESENT. WINDS WILL FINALLY WEAKEN  
THURSDAY AFTERNOON.  
 

 
   
CYS WATCHES/WARNINGS/ADVISORIES
 
 
WY...HIGH WIND WARNING UNTIL 5 AM MST THURSDAY FOR WYZ101-104-106-  
107-109-110-115>118.  
NE...NONE.  
 

 
 

 
 
SHORT TERM...MAC  
LONG TERM...MM  
AVIATION...MN  
 
CLICK HERE TO GO TO PREVIOUS BULLETINS.

The Nexlab WY Page
The Nexlab NE Page Main Text Page