513
FXUS65 KCYS 181729
AFDCYS
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
1029 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.
UPDATE
ISSUED AT 1029 AM MST WED DEC 18 2024
MOSTLY HIGH BASED CLOUDS MOVING THROUGH OUR AREA. STILL
EXPECTING THE WINDS TO START TO GUST IN OUR WIND PRONE AREAS
THIS EVENING INTO TOMORROW MORNING. AS WE PROGRESS THROUGH THE
DAY OUR WARMER TEMPERATURES SHOULD MELT OFF WHAT LITTLE SNOW WE
HAD INTO OUR VALLEY AND LOWER ELEVATION AREAS, THE MOUNTAINS
WILL STILL KEEP THEIR SNOW.
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 /18Z TAFS THROUGH 18Z THURSDAY/
ISSUED AT 1029 AM MST WED DEC 18 2024
VFR CONDITIONS ARE EXPECTED THROUGH THE TAF PERIOD. WINDS ARE
STILL EXPECTED TO GUST AS HIGH AS 50KTS STARTING IN THE LATE
AFTERNOON TO EARLY EVENING. AROUND 03Z LOW-LEVEL WIND SHEAR WILL
REALLY START TO RAMP UP BETWEEN 50 TO 60 KNOTS AT TIMES AT
AROUND 2,000 FT AGL. NOT EXPECTING TO HAVE ANY VISIBILITY OR
CLOUD ISSUES DURING THIS PERIOD.
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.
UPDATE...
SHORT TERM...RUBIN
LONG TERM...TJT
AVIATION...MM
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