872
FXUS65 KCYS 222335
AFDCYS
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
435 PM MST SUN DEC 22 2024
KEY MESSAGES
- A HIGH WIND WARNING REMAINS IN EFFECT FOR THE WIND PRONE
AREAS OF SOUTHEAST WYOMING UNTIL EARLY THIS EVENING.
- MOUNTAIN SNOW LIKELY, BEGINNING TONIGHT AND CONTINUING
THROUGH MONDAY.
- ACTIVE PATTERN EXPECTED MID-WEEK ONWARDS WITH DAILY CHANCES
FOR SNOW IN THE MOUNTAINS AND SMALL CHANCES FOR SOME SNOW
ACROSS THE LOWER ELEVATIONS. STRONG WINDS LOOK TO RETURN FOR
THE WEEKEND.
SHORT TERM /THROUGH TUESDAY NIGHT/
ISSUED AT 155 PM MST SUN DEC 22 2024
LATEST WATER VAPOR LOOP WAS STILL SHOWING SOME MOUNTAIN WAVE TURBULENCE
ALONG AND WEST OF THE LARAMIE RANGE. THIS COMBINED WITH THE
STRONG WINDS ALOFT AND TIGHT PRESSURE GRADIENTS IS RESULTING IN
GUSTY WINDS AT SPEEDS 30 TO 40 WITH GUSTS TO 55 TO 60 MPH
BETWEEN CHEYENNE AND ARLINGTON. THE SHORTWAVE THAT HAS INDUCED
THESE STRONGER WINDS ALOFT WILL CONTINUE TO PUSH EAST TO THE
NORTHERN PLAINS TONIGHT. AS THIS OCCURS, WE WILL CONTINUE TO SEE
A SHALLOW FRONTAL BOUNDARY CURRENTLY DEPICTED BETWEEN WHEATLAND
AND TORRINGTON PUSH SOUTHWARD ACROSS THE REMAINDER OF THE
FORECAST AREA THIS EVENING. THIS FRONT SHOULD PASS THROUGH THE
REMAINDER OF PLATTE COUNTY DURING THE NEXT HOUR OR SO. AS A
RESULT, WE WENT AHEAD AND CANCELLED THE HIGH WIND WARNING FOR
BORDEAUX AND PLATTE COUNTY. MEANWHILE, WE HAVE KEPT THE HIGH
WIND WARNING GOING FOR AREAS THE I-80 SUMMIT AND FOOTHILLS UNTIL
5PM AND THE ARLINGTON AREA UNTIL 8PM. THE WIND SPEEDS IN
ARLINGTON MAY HANG ON A BIT LONGER DUE TO THE CAG-CPR PRESSURE
GRADIENT TENDING TO HANG ON A BIT LONGER BEFORE THE NEXT
SHORTWAVE ARRIVES.
LATER THIS EVENING, THE MODELS ARE SHOWING SOME DECENT
SATURATION TAKING PLACE OVER THE SIERRA MADRE/SNOWY MOUNTAIN
RANGES. THIS COMBINED WITH GOOD OROGRAPHICS IS FAVORING DECENT
SNOWFALL OVER THOSE AREAS TONIGHT AND MONDAY. RATES DON'T LOOK
ALL THAT IMPRESSIVE AT THIS POINT, DUE TO LACK OF INSTABILITY.
HOWEVER, IT WILL CERTAINLY BE BENEFICIAL FOR THESE AREAS. WE
ELECTED NOT TO ISSUE ANY HEADLINES AT THIS POINT, DUE TO LIMITED
DYNAMICS AND BETTER FORCING IN THE COLORADO MOUNTAINS. THE REST
OF THE FORECAST AREA WILL BE LOOKS MOSTLY DRY WITH MORE
DOWNSLOPE CONDITIONS FAVORING ABOVE NORMAL TEMPERATURES
EXCEPT WEST OF THE LARAMIE RANGE WHERE THE CLOUD COVER WILL
DOMINATE THE AREA.
A SHARP UPPER LEVEL RIDGE IS EXPECTED BUILD OVER THE AREA ON
TUESDAY AND BRING ANOTHER RATHER MILD DAY TO THE AREA WITH LIGHT
WIND SPEEDS. HOWEVER, WE WILL SEE AN INCREASE IN CLOUD COVER
THAT MAY LIMIT HIGH TEMPERATURES A BIT AS OUR NEXT UPPER LEVEL
TROF APPROACHES. SNOWFALL WILL ALSO BE ON THE INCREASE ACROSS
AREAS WEST OF I-25 ON CHRISTMAS EVE NIGHT MAINLY IN THE
MOUNTAINS AND PERHAPS HIGHER PLAINS WHERE THEY COULD WAKE UP TO
SOME LIGHT SNOW ON CHRISTMAS MORNING.
LONG TERM /WEDNESDAY THROUGH SUNDAY/
ISSUED AT 155 PM MST SUN DEC 22 2024
A PROGRESSIVE AND ACTIVE SYNOPTIC PATTERN REMAINS THE MAIN FOCUS OF
THE LONG TERM FORECAST FROM WEDNESDAY MORNING THROUGH THE WEEKEND.
BY WEDNESDAY, THE UPPER-LEVEL TROUGH WILL HAVE BEEN PUSHED OFF TO
THE EAST AND SITS OVER THE CENTRAL PLAINS WEDNESDAY MORNING. AN
INCOMING UPPER-LEVEL TROUGH SITS JUST TO THE WEST OF THE CWA, WITH
THE TROUGH AXIS RUNNING THROUGH IDAHO AND UTAH. A STRONG, 150KT JET
SITS ON THE WESTERN FLANK OF THE TROUGH, WITH A BUILDING RIDGE JUST
OFF THE COAST. SOUTHWESTERLY FLOW ALOFT TURNS MORE SOUTHERLY AS THE
TROUGH MOVES EASTWARD, DEVELOPING A CLOSED LOW BY WEDNESDAY NIGHT.
THIS 250MB, CLOSED LOW SITS JUST SOUTH OF THE CWA IN THE GFS, WITH
THE ECMWF SUGGESTING AN OPEN WAVE THROUGH THURSDAY MORNING. THE OPEN
WAVE APPEARS TO BE MORE FAVORED ACROSS THE LONG RANGE MODELS, WITH
THE ECMWF AND THE GEFS/GEPS BOTH SUGGESTING AN OPEN WAVE, RATHER
THAN A DEVELOPING CLOSED LOW. DESPITE THIS, PRECIPITATION DOES LOOK
TO BE FAVORED ACROSS PORTIONS OF THE CWA, ESPECIALLY IN THE SIERRA
MADRE AND SNOWY RANGES. FURTHER DOWN AT 700MB, A CLOSED LOW IS
PROGGED TO DEVELOP IN THE GFS, ECMWF, LREF, AND OTHER MEDIUM TO LONG
RANGE MODELS. THE EXACT PLACEMENT OF THIS LOW REMAINS UNCERTAIN AT
THIS TIME, WITH THE GFS AND ECMWF SHOWING THE LOW OVER
SOUTHEASTERN COLORADO AND THE LREF SUGGESTING A LARGER LOW
SPANNING MUCH OF EASTERN COLORADO. THE SURFACE LOW IS CURRENTLY
PROGGED TO BE STACKED WITH THE 700MB IN MOST MEDIUM TO LONG
RANGE MODELS, SUGGESTING DECENT AGREEMENT OF A STACKED LOW
SOMEWHERE OVER EASTERN/SOUTHEASTERN COLORADO. PRIMARILY
NORTHERLY SURFACE FLOW IS EXPECTED LEADING TO THE POTENTIAL FOR
UPSLOPE FLOW ALONG THE CHEYENNE RIDGE AND THE HIGHER ELEVATIONS
OF CARBON AND ALBANY COUNTIES. BOTH THE GFS AND ECMWF SHOW
ISENTROPIC UPGLIDE ACROSS WESTERN PORTIONS OF THE REGION ON
WEDNESDAY. COMBINED WITH UPSLOPE FLOW ALONG THE SIERRA MADRES
AND SNOWY RANGE, MOUNTAIN SNOWFALL IS EXPECTED, POTENTIALLY
REACHING ADVISORY CRITERIA FOR WEDNESDAY. ISENTROPIC DOWNGLIDE
CONTINUES TO BE FAVORED EAST OF THE LARAMIE RANGE IN THE GFS
WITH WEAK UPGLIDE FAVORED IN THE ECMWF. THE NAEFS CONTINUES TO
SUGGEST PWATS IN THE 90TH PERCENTILE DURING THIS TIME,
INCREASING CONCERNS FOR SNOW ACROSS THE REGION. IF THE SURFACE
LOW TRENDS SLIGHTLY FURTHER NORTH, SIGNIFICANTLY MORE SNOW MAY
BE EXPECTED ALONG THE I-80 CORRIDOR AS WINDS TURN EASTERLY AND
WRAP- AROUND MOISTURE SURGES INTO THE REGION. HOWEVER, IF THE
SOUTHERLY TRACK REMAINS, LESS SNOW FALL WILL BE EXPECTED.
DISAGREEMENT IN THE EVOLUTION OF THE UPPER-LEVEL TROUGH CONTINUES
BETWEEN THE ECMWF AND GFS, WITH THE GFS SUGGESTING THE CLOSED, UPPER-
LEVEL LOW WILL ACCELERATE TO THE NORTH, WHILE THE ECMWF KEEPS THE
LOW PROGRESSING OFF TO THE EAST. DESPITE THIS DISAGREEMENT, BOTH
MODELS BRING ANOTHER UPPER-LEVEL TROUGH TOWARDS THE REGION
THROUGHOUT THE DAY THURSDAY. AT 700MB, THE CLOSED LOW EJECTS OFF TO
THE NORTH IN THE GFS AND MORE EASTERLY TO NORTHEASTERLY IN THE
ECMWF. THE GFS SOLUTION TIGHTENS HEIGHT GRADIENTS ACROSS THE REGION
AS THE 700MB LOW SLIDES ACROSS CENTRAL NEBRASKA, LEADING TO THE
POTENTIAL FOR STRONG WINDS ON THURSDAY. THE ECMWF ALSO SUGGESTS
STRONGER WINDS FOR THURSDAY, BUT INSTEAD IS DUE TO THE INCOMING
700MB TROUGH TIGHTENING HEIGHT GRADIENTS. EITHER SOLUTION STILL
BRINGS STRONG WINDS BACK INTO SOUTHEAST WYOMING THURSDAY INTO
FRIDAY. CRAIG TO CASPER GRADIENTS ARE FAIRLY GOOD THURSDAY MORNING,
WITH 60M AT 850MB AND 55M AT 700MB. IN HOUSE RANDOM FOREST GUIDANCE
IS NOT EXCITED ABOUT THIS SET UP, LIKELY DUE TO THE UNCERTAINTY IN
THE MODELS. THEREFORE, INCREASED WINDS TO BE ELEVATED, BUT REMAINED
WELL BELOW HIGH WIND CRITERIA. IN ADDITION TO THE WINDS ON THURSDAY,
MOUNTAIN SNOW WILL CONTINUE THROUGH THURSDAY AS UPSLOPE FLOW
CONTINUES ACROSS THE RANGES. WITH SEASONAL PWAT VALUES ACROSS THE
RANGES, BENEFICIAL SNOW WILL CONTINUE TO FALL THROUGHOUT THE LONG
TERM PERIOD, BUT NO MAJOR RATES OR SNOWFALL TOTALS ARE EXPECTED AT
THIS TIME.
THE UPPER-LEVEL TROUGH SLOWLY PUSHES ACROSS THE REGION ON FRIDAY,
WITH MORE ZONAL FLOW DEVELOPING ALONG THE WEST COAST IN THE UPPER-
LEVEL AND FURTHER DOWN AROUND 700MB. FRIDAY LOOKS TO BE FAIRLY NICE
WEATHER WISE AS STRONG WINDS DECREASE INTO FRIDAY MORNING AND
ELEVATED WINDS CONTINUE THROUGH MOST OF THE DAY. WITH ZONAL FLOW
DEVELOPING AT 700MB, PRECIPITATION CHANCES OUTSIDE OF THE MOUNTAINS
DROP TO NEAR-ZERO AND THE POTENTIAL FOR STRONG WINDS INCREASES
TOWARDS FRIDAY EVENING. A 700MB SHORTWAVE IS MODELED TO TRAVERSE
ACROSS THE REGION, LEADING TO STRENGTHENING 700MB HEIGHT GRADIENTS
AND A JET AROUND 45 TO 50KTS DEVELOPING ACROSS THE LARAMIE RANGE. BY
SATURDAY MORNING, STRONG DOWNWARD OMEGAS DEVELOP ACROSS THE LARAMIE
RANGE WITH CRAIG TO CASPER GRADIENTS INCREASING INTO THE 70S AND 80S
AT THIS TIME. IN HOUSE RANDOM FOREST GUIDANCE ALSO BEGINS TO FAVOR
HIGH WINDS SATURDAY WITH PROBABILITY INCREASING TO AROUND 80%.
HOWEVER, THIS EVENT IS STILL ABOUT A WEEK OUT, SO SOME OF THESE
VARIABLES MAY CHANGE OVER THE NEXT SEVERAL DAYS. IT STILL LOOKS TO
BE A FAIRLY WINDY WEEKEND ONCE AGAIN FOR SOUTHEAST WYOMING.
TEMPERATURES FROM MID-WEEK ONWARDS WILL BEGIN TO APPROACH NEAR-
NORMAL, WITH HIGHS IN THE 40S EAST OF THE LARAMIE RANGE AND HIGHS IN
THE 30S WEST OF THE LARAMIE RANGE. THESE ARE STILL ABOVE AVERAGE FOR
THIS TIME OF YEAR, BUT IT MAY FEEL A LITTLE COOLER AS TEMPERATURES
STRUGGLING TO GET OUT OF THE 40S. WITH THE POTENTIAL FOR STRONG
WINDS SATURDAY AND SUNDAY, TEMPERATURES EAST OF THE LARAMIE RANGE
INCREASE TO WELL ABOVE AVERAGE IN THE MID-50S DUE TO THE POTENTIAL
FOR DOWNSLOPE WARMING WITH THE STRONG WINDS THESE DAYS. OVERALL,
ABOVE AVERAGE TEMPERATURES CONTINUE, BUT THE END OF THE WEEK MAY
FEEL SLIGHTLY COOLER THAN PREVIOUS DAYS AS HIGHS REMAIN IN THE
40S.
AVIATION /00Z TAFS THROUGH 00Z TUESDAY/
ISSUED AT 433 PM MST SUN DEC 22 2024
A WEAK STORM SYSTEM PASSING THROUGH THE AREA TONIGHT MAY BRING
A PERIOD OF VIS/CIG REDUCTIONS TO KRWL, AND POSSIBLY KLAR. LOOK
FOR A FEW SNOW SHOWERS MAINLY BETWEEN 05Z AND 09Z AROUND KRWL,
TRANSITIONING TO MVFR TO IFR CIGS THROUGH MID MORNING MONDAY.
ELSEWHERE, EXPECT VFR CONDITIONS. WIND GUSTS OF AROUND 25 KNOTS
WILL RETURN TO WYOMING MONDAY MID-MORNING, BUT EXPECT FAIRLY
LIGHT WINDS AT NEBRASKA TERMINALS THROUGH THE FORECAST PERIOD.
CYS WATCHES/WARNINGS/ADVISORIES
WY...HIGH WIND WARNING UNTIL 8 PM MST THIS EVENING FOR WYZ110.
HIGH WIND WARNING UNTIL 5 PM MST THIS AFTERNOON FOR WYZ116-117.
NE...NONE.
SHORT TERM...REC
LONG TERM...AM
AVIATION...MN
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