134
FXUS65 KCYS 211700
AFDCYS
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
1000 AM MST SAT DEC 21 2024
KEY MESSAGES
- MILD AND DRY WEATHER WILL CONTINUE THIS WEEKEND. WINDY
CONDITIONS EXPECTED ON SUNDAY.
- A HIGH WIND WATCH IS IN EFFECT FOR THE WIND PRONE AREAS OF
SOUTHEAST WYOMING BEGINNING LATE SATURDAY EVENING AND
CONTINUING THROUGH SUNDAY AFTERNOON.
- 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 SUNDAY NIGHT/
ISSUED AT 230 AM MST SAT DEC 21 2024
A PRETTY QUIET WEATHER PATTERN EXPECTED THIS WEEKEND FOR MOST
AREAS WITH LOCALLY STRONG WINDS A POSSIBILITY FOR THE WIND PRONE
AREAS OF SOUTHEAST WYOMING. FOR TODAY, UPPER LEVEL RIDGE AXIS
WILL MOVE INTO WYOMING AND COLORADO WITH INTERVALS OF MID TO
HIGH CLOUDS MOVING NORTHWEST TO SOUTHEAST AT TIMES. RELATIVELY
LIGHT WINDS ARE FORECAST TODAY WITH LOCALLY BREEZY CONDITIONS
EXPECTED THIS AFTERNOON FOR MOST OF SOUTHEAST WYOMING. IT WILL
BE PRETTY MILD TODAY WITH HIGH TEMPERATURES SIMILAR TO YESTERDAY
AND GENERALLY IN THE 50S TO LOW 60S FOR MOST LOCATIONS. EXPECT
UPPER 40S TO MID 50S FOR THE HIGH VALLEYS OF CARBON COUNTY THIS
AFTERNOON.
FOR TONIGHT AND SUNDAY, MODELS CONTINUE TO SHOW A FAST MOVING
PACIFIC UPPER LEVEL TROUGH EJECTING EASTWARD ACROSS MONTANA. A
DRY COOL FRONT IS EXPECTED TO PUSH SOUTHEAST ACROSS THE AREA
WITH SLIGHTLY COOLER TEMPERATURES FOR SUNDAY, BUT STILL
REMAINING WELL ABOVE NORMAL. THE ONLY CONCERN WITH THIS EVENT IS
WINDY CONDITIONS AND THE POTENTIAL FOR STRONG GUSTY WINDS
STARTING AS EARLY AS 9 PM SATURDAY MAINLY FOR THE WIND PRONE
AREAS. EARLIER ENSEMBLE AND DETERMINISTIC MODEL DATA SUGGESTED A
MORE WIDESPREAD WIND EVENT ASSOCIATED WITH THIS PACIFIC TROUGH,
BUT MODELS HAVE BACKED OFF ON THE AREAL EXTENT OF THE STRONGEST
WINDS. THE WIND PRONE AREAS, SUCH AS ARLINGTON, BORDEAUX, AND
PORTIONS OF THE SOUTHERN LARAMIE RANGE, STILL LOOK GOOD WITH
700MB WINDS 50 TO 65 KNOTS AND A SOLID NEAR-SURFACE PRESSURE
GRADIENT ALONG THE SPINE OF THE LARAMIE RANGE AND THE SNOWY
RANGE. DID WANT TO NOTE, THESE WINDS ARE NOT QUITE AS STRONG AS
24 TO 48 HOURS AGO, BUT SHOULD BE ENOUGH TO REACH CRITERIA WITH
GOOD LOW LEVEL SUBSIDENCE. THE MOST FAVORABLE LOCATIONS BASED
ON GUIDANCE AND IN-HOUSE WIND MODELING IS BORDEAUX...WHICH MAY
SEE GUSTS OVER 70 MPH FOR A TIME EARLY SUNDAY MORNING. THE OTHER
WIND PRONE AREAS SHOULD SEE GUSTS AROUND 65 MPH THROUGH EARLY
SUNDAY AFTERNOON. THEREFORE, ISSUED A HIGH WIND WATCH STARTING
AT 8 PM THIS EVENING. THIS IS A LITTLE EARLY, BUT THESE WIND
EVENTS TEND TO ARRIVE A FEW HOURS EARLIER THAN EXPECTED. THE
BAND OF STRONGEST WINDS IS A LITTLE NARROWER COMPARED TO A FEW
DAYS AGO, BUT IT SHOULD BE ENOUGH TO INCLUDE THE INTERSTATE 80
SUMMIT IN THE WATCH. THE BIG QUESTION IS THE SUB- WIND PRONE
AREAS INCLUDING THE LARAMIE VALLEY, CHEYENNE, RAWLINS, AND THE
I-25 CORRIDOR EAST OF CASPER TO EASTERN PLATTE COUNTY. MODELS
AND IN- HOUSE GUIDANCE HAS TRENDED CONSIDERABLY LOWER WITH
PROBABILITIES COMPARED TO A FEW DAYS AGO, SO LEFT THESE OUT OF
THE HIGH WIND WATCH FOR NOW. THE REASONING FOR THIS APPEARS TO
BE SURFACE PRESSURE TENDENCIES BECOME MORE POSITIVE EARLIER ON
SUNDAY ACROSS THE HIGH PLAINS, WHICH ISN'T FAVORABLE FOR A MORE
WIDESPREAD WIND EVENT...IN ADDITION TO LOWER THAN AVERAGE
SUBSIDENCE. WITH ALL THAT SAID, WILL CONTINUE TO MONITOR THE
SUB-WIND PRONE AREAS THROUGH SUNDAY SINCE STRONG WINDS CAN'T BE
TOTALLY RULED OUT. FOR NOW, KEPT SUSTAINED WINDS BETWEEN 25 TO
35 MPH WITH OCCASIONAL GUSTS OF 45 MPH. OTHERWISE, EXPECT SOME
MOUNTAIN SNOW TO DEVELOP SUNDAY NIGHT AS THE MIDLEVEL FLOW
BECOMES MORE WESTERLY AHEAD OF THE NEXT PACIFIC SYSTEM.
LONG TERM /MONDAY THROUGH FRIDAY/
ISSUED AT 213 AM MST SAT DEC 21 2024
MONDAY...SCATTERED TO NUMEROUS SNOW SHOWERS WILL OCCUR ACROSS THE
SNOWY AND SIERRA MADRE RANGES, MOST NUMEROUS FOR THE SIERRA MADRES,
AS THE NEXT SHORTWAVE TROUGH ALOFT MOVES INTO WESTERN WYOMING,
SPREADING OROGRAPHIC AND DYNAMIC SNOWS INTO THE REGION. TEMPERATURES
WILL BE COOLER THAN SUNDAY AREAWIDE DUE TO CLOUD COVER AND 700 MB
TEMPERATURES ONLY NEAR -3 CELSIUS.
TUESDAY...A DRIER AND COOLER DAY IS ON TAP IN THE WAKE OF THE
SHORTWAVE TROUGH ALOFT AND WITH 700 MB TEMPERATURES NEAR -6 CELSIUS.
CHRISTMAS...A TRANSITORY RIDGE ALOFT MOVES OVERHEAD EARLY IN THE
DAY, IN ADVANCE OF THE NEXT PROGRESSIVE SHORTWAVE TROUGH ALOFT
MOVING OVER COLORADO. THE TRAJECTORY OF THIS TROUGH SUGGESTS THAT
MOST OF THE SNOW ASSOCIATED WITH THE SYSTEM WILL REMAIN TO OUR SOUTH
ACROSS COLORADO, THOUGH WE WILL STILL SEE CHANCES FOR SNOW OVER AND
NEAR OUR SNOWY AND SIERRA MADRE RANGES. 700 MB TEMPERATURES NEAR
-4 CELSIUS WILL YIELD HIGH TEMPERATURES MAINLY IN THE 40S.
THURSDAY...A PRIMARILY DRY DAY IS EXPECTED WITH A SHORTWAVE RIDGE
MOVING OVERHEAD, ALTHOUGH THERE WILL BE A CHANCE OF AFTERNOON
OROGRAPHIC SNOW SHOWERS FOR THE SIERRA MADRE RANGE IN ADVANCE OF THE
NEXT SHORTWAVE TROUGH ALOFT.
FRIDAY...ANOTHER SHORTWAVE TROUGH ALOFT MOVES OVERHEAD, SPREADING
OROGRAPHIC SNOW SHOWERS OVER OUR SNOWY AND SIERRA MADRE RANGES,
THOUGH WITH MINIMAL PRECIPITATION ELSEWHERE AS THE SYSTEM IS
MOISTURE LACKING. 700 MB TEMPERATURES NEAR -6 CELSIUS WILL YIELD
MAXIMUM TEMPERATURES IN THE UPPER 30S WEST OF I-25, WITH MID 40S TO
LOWER 50S EAST OF I-25.
AVIATION /18Z TAFS THROUGH 18Z SUNDAY/
ISSUED AT 1000 AM MST SAT DEC 21 2024
SIGNIFICANT UPDATES TO THE 24 HOUR TAFS, PRIMARILY ACROSS
WESTERN NEBRASKA, WHERE LLWS WILL BE THE MAIN CONCERN THROUGHOUT
THE OVERNIGHT HOURS FOR SOUTHEAST WYOMING AND THE NEBRASKA
PANHANDLE. TONIGHT THROUGH SUNDAY, THE NEXT PROGRESSIVE UPPER
LEVEL TROUGH WILL CONTINUE TO DIG ACROSS MONTANA AND INTO THE
DAKOTAS. MOSTLY A WIND FORECAST EXPECTED ACROSS THE TERMINALS,
WITH THE PRIMARY PACIFIC SYSTEM TIGHTENING FOR WYOMING AND
LATER INTO NEBRASKA AS A LOW LEVEL JET BEGINS TO DEVELOP ON THE
SOUTHERN EDGE OF THE SYSTEM. MAIN TAF EDITS INCLUDE LLWS ACROSS
THE MAJORITY OF TERMINAL INTO THE OVERNIGHT HOURS WHEN THE
ATMOSPHERE IS EFFECTIVELY DECOUPLED. ONCE PROPER MIXING IS ABLE
TO BE ACHIEVED IN THE MORNING HOURS, WILL SEE THOSE WINDS MIX
DOWN TOWARDS THE SURFACE, WITH GUSTY TO STRONGER WINDS POSSIBLE
TOMORROW MORNING.
CYS WATCHES/WARNINGS/ADVISORIES
WY...HIGH WIND WATCH FROM 8 PM MST THIS EVENING THROUGH SUNDAY
AFTERNOON FOR WYZ106-110-116-117.
NE...NONE.
SHORT TERM...TJT
LONG TERM...RUBIN
AVIATION...MRD
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