654
FXUS65 KCYS 201155
AFDCYS
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
455 AM MST FRI DEC 20 2024
KEY MESSAGES
- ANOTHER HIGH WIND EVENT IS POSSIBLE FOR TODAY AND EARLY THIS EVENING
FOR ARLINGTON, BORDEAUX AND THE INTERSTATE 80 SUMMIT.
TEMPERATURES WILL BE MORE MILD TODAY ACROSS THE AREA.
- THE WEEKEND WILL CONTINUE MILD AND DRY WITH ANOTHER HIGH WIND EVENT
POSSIBLE FOR SUNDAY AND SUNDAY NIGHT ACROSS PORTIONS OF
SOUTHEAST WYOMING.
- SOMEWHAT COOLER TEMPERATURES WILL DEVELOP FOR MONDAY THROUGH CHRISTMAS
DAY WITH A CHANCE OF SNOW FOR THE SNOWY AND SIERRA MADRE
RANGES FOR MONDAY, AND AGAIN FOR THE MOUNTAINS AND NEARBY
LOWER ELEVATIONS FOR CHRISTMAS DAY.
SHORT TERM /THROUGH SATURDAY NIGHT/
ISSUED AT 226 AM MST FRI DEC 20 2024
TODAY...THE INHERITED HIGH WIND WATCH FOR THE WIND PRONE LOCATIONS
OF ARLINGTON, BORDEAUX AND THE I-80 SUMMIT LOOKS ON TRACK AS LOW AND
MID LEVEL GRADIENTS STRENGTHEN THIS MORNING, WITH THE CRAIG-CASPER
850/700 MB HEIGHT DIFFERENCES INCREASING FROM 54/37 METERS AT 06Z,
TO 78/49 METERS BY 15Z AND REMAINING AT 64/40 METERS BY 00Z. IN
ADDITION, THE LOCAL WIND MODELS SUGGEST STRENGTHENING WINDS AS WELL
AS THE GFS 700 MB WIND PROGS OF 45 TO 50 KNOTS. WILL DEFINITELY SEE
WINDS INCREASING THIS MORNING ACROSS THE WIND PRONE LOCATIONS OF
SOUTHEAST WYOMING, BUT CONFIDENCE IS STILL NOT HIGH ENOUGH TO
WARRANT AN UPGRADE TO A HIGH WIND WARNING, THUS WE WILL LEAVE THE
WATCH INTACT FOR NOW AND MONITOR THE WINDS THROUGH THE EARLY MORNING
HOURS.
ANOTHER WARMING TREND IS EXPECTED WITH 700 MB TEMPERATURES
REBOUNDING TO NEAR 3 CELSIUS, AND A SURFACE LEE TROUGH DEVELOPMENT,
PRODUCING DOWNSLOPE WINDS, AND HELPING MAXIMUM TEMPERATURES TO CLIMB
TO THE UPPER 40S TO UPPER 50S. IT WILL ALSO FEEL PARTICULARLY WARMER
DUE TO WEAKER LOW LEVEL GRADIENTS AND LESS WIND OUTSIDE OF THE WIND
PRONE LOCATIONS.
TONIGHT...RIDGING ALOFT MOVES OVER CENTRAL WYOMING AND WITH A
MODERATING AIRMASS, MINIMUM TEMPERATURES WILL BE NOT AS COLD AS
THURSDAY NIGHT. CONTINUED DRY WITH THE LACK OF LOW AND MID LEVEL
MOISTURE.
SATURDAY...RIDGING OVER WYOMING FLATTENS OUT WITH THE FLOW ALOFT
BECOMING ZONAL, OR WEST TO EAST. THE ZONAL FLOW ALOFT AND A
DEVELOPING SURFACE LEE TROUGH WILL HELP TEMPERATURES TO BE EVEN
WARMER, WITH 700 MB TEMPERATURES NEAR 4 CELSIUS YIELDING MAXIMUM
TEMPERATURES FROM THE UPPER 40S TO LOWER 60S. WINDS WILL BE EVEN
LESS THAN TODAY WITH RELATIVELY WEAK LOW AND MID LEVEL GRADIENTS.
SATURDAY NIGHT...A FAST MOVING AND LOW AMPLITUDE SHORTWAVE TROUGH
ALOFT MOVES ACROSS WYOMING, PRODUCING ENOUGH MIXING AND A MODERATING
AIRMASS TO MAKE FOR EVEN MORE MILD OVERNIGHT LOW TEMPERATURES.
LONG TERM /SUNDAY THROUGH THURSDAY/
ISSUED AT 226 AM MST FRI DEC 20 2024
MODELS REMAIN IN GOOD AGREEMENT LATE THIS WEEKEND THROUGH
TUESDAY NIGHT WITH RELATIVELY SMALL ENSEMBLE SPREADS MOST DAYS.
MODELS CONTINUE TO SHOW AN UPPER LEVEL RIDGE AXIS TRANSLATING
EASTWARD OVER THE AREA AND INTO THE GREAT PLAINS. AS SOUTHWEST
FLOW ALOFT DEVELOPS ACROSS THE AREA WEST OF THE RIDGE AXIS,
DAYTIME TEMPERATURES WILL BE PLEASANT FOR THIS TIME OF THE YEAR
AND GENERALLY IN THE UPPER 40S TO UPPER 50S, WARMEST ALONG AND
EAST OF THE INTERSTATE 25 CORRIDOR INTO WESTERN NEBRASKA. IT
WILL REMAIN DRY ON SUNDAY AS A PROGRESSIVE PACIFIC UPPER LEVEL
TROUGH QUICKLY MOVES ACROSS MONTANA AND INTO THE DAKOTAS. MODELS
HAVE CONTINUED TO TREND NORTHWARD WITH THIS SYSTEM, SO
PRECIPITATION IS NOT EXPECTED. HOWEVER, WINDY CONDITIONS AND
THE POTENTIAL FOR STRONG WINDS ARE EXPECTED SUNDAY THROUGH EARLY
MONDAY. THIS POTENTIAL IS LIMITED HOWEVER WITH THE NORTHWARD
JOG OF THE UPPER LEVEL TROUGH. IN-HOUSE WIND GUIDANCE HAS
TRENDED A LITTLE LOWER WITH PEAK WINDS SPEEDS AND COVERAGE OF
STRONG WINDS ACROSS SOUTHEAST WYOMING. WIND PRONE AREAS STILL
LOOK LIKE A GOOD BET FOR GUSTS OVER 58 MPH, BUT MOST MODELS ARE
NOT SHOWING 700MB WIND SPEEDS OVER 70 KNOTS FOR ALL THAT LONG
SUNDAY MORNING. 300MB JET STREAM IS NOW QUITE A BIT FURTHER
NORTH AS WELL. KEPT SURFACE WINDS CLOSE TO PREVIOUS FORECASTS
FOR NOW, BUT TRENDED WINDS DOWN CLOSER TO MOS GUIDANCE OUTSIDE
OF THE WIND PRONE AREAS. STILL LOOKS LIKE A GOOD EVENT FOR
SOUTHEAST WYOMING, BUT AREAS OUTSIDE OF THE WIND PRONE AREAS
JUST LOOK WINDY (20 TO 35 MPH WINDS) AT THIS TIME INSTEAD OF
WIDESPREAD STRONG WINDS ALONG THE I-25 AND I-80 CORRIDORS.
AS WE HEAD INTO NEXT WEEK, A MINOR PATTERN SHIFT IS EXPECTED
BEHIND SUNDAY'S 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. THE MAIN SHORTWAVE IS FORECAST TO DIG
SOUTH ACROSS THE ROCKY MOUNTAIN REGION MONDAY AND MONDAY NIGHT.
MOUNTAIN SNOWFALL IS FORECAST TO INCREASE ON MONDAY WITH LITTLE
OR NO ACTIVITY IN THE LOWER ELEVATIONS. THE BEST FORCING AND
MOISTURE WITH THIS QUICK MOVING SHORTWAVE REMAINS OVER CENTRAL
WYOMING AND NORTH CENTRAL COLORADO. INCREASED POP CLOSER TO
LIKELY CRITERIA FOR SNOW ACROSS THE MOUNTAINS WITH LOWER VALUES
ACROSS THE LOWER ELEVATIONS INTO TUESDAY MORNING. EXPECT VERY
LITTLE OF THIS SNOWFALL TO MAKE IT ALL THE WAY TO THE I-25
CORRIDOR OR INTO WESTERN NEBRASKA. KEPT POP BELOW 5 PERCENT
ACROSS THE HIGH PLAINS.
FOR CHRISTMAS DAY AND LATER NEXT WEEK, DETERMINISTIC MODELS
HAVE BACKED OFF ON THE POTENTIAL SNOW FOR CHRISTMAS DAY.
HOWEVER, NEARLY HALF OF THE ENSEMBLE MEMBERS STILL SHOW SOME
PRECIPITATION ALONG THE I-80 CORRIDOR. MODELS HAVE TRENDED
SOUTHWARD WITH THE PACIFIC UPPER LEVEL TROUGH AND NOTABLY
WEAKER AS IT EJECTS TO THE EAST RELATIVELY FAST BY EARLY
THURSDAY. KEPT POP AROUND 20 TO 40 PERCENT FOR MOST OF THE
AREA...ESPECIALLY FURTHER SOUTH NEAR THE COLORADO BORDER WITH
HIGHER POP ACROSS THE MOUNTAINS. THANKFULLY, IT DOESN'T LOOK
LIKE A WINDY PATTERN FOR SOUTHEAST WYOMING MID TO LATE NEXT
WEEK.
AVIATION /12Z TAFS THROUGH 12Z SATURDAY/
ISSUED AT 455 AM MST FRI DEC 20 2024
A WEAK DISTURBANCE ALOFT WILL REMAIN NORTHEAST OF THE AREA TODAY
AS UPPER LEVEL RIDGING BUILDS OVER THE INTERMOUNTAIN WEST AND
ROCKY MOUNTAIN REGION.
HAZARDS/WEATHER TRENDS: VFR CONDITIONS WILL CONTINUE TODAY AND
TONIGHT. LOW CONFIDENCE WITH WIND SPEEDS LATE THIS MORNING AND THIS
AFTERNOON WITH 35 TO 45 KNOT WINDS AROUND 2K TO 4K FEET AGL. EXPECT
SOME HIGH CLOUD COVER TO LIMIT GOOD LOW LEVEL MIXING, SO KEPT GUSTS
AROUND 25 TO 30 KNOT RANGE FOR NOW FOR MOST TERMINALS.
CYS WATCHES/WARNINGS/ADVISORIES
WY...HIGH WIND WATCH THROUGH THIS EVENING FOR WYZ106-110-116.
NE...NONE.
SHORT TERM...RUBIN
LONG TERM...TJT
AVIATION...TJT
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