675
FXUS65 KCYS 162316
AFDCYS
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
416 PM MST TUE DEC 16 2025
KEY MESSAGES
- WIDESPREAD STRONG TO LOCALLY DAMAGING WINDS WILL RETURN
WEDNESDAY INTO THURSDAY MORNING. ANOTHER SIGNIFICANT WIND
EVENT IS EXPECTED THURSDAY NIGHT INTO FRIDAY.
- I-25 WIND PRONE AREAS CAN EXPECT WIND GUSTS UP TO 90 MPH
WEDNESDAY, PARTICULARLY IN PLATTE COUNTY.
- WIDESPREAD GUSTS OF 60 TO 80 MPH ARE EXPECTED WEDNESDAY IN
SOUTHEAST WYOMING. THIS WILL TRANSITION TO GUSTS OF 55 TO 65
MPH OVER THE HIGH PLAINS WEDNESDAY NIGHT INTO THURSDAY MORNING
BEHIND A COLD FRONT.
- HIGH GRASSLAND WILDFIRE DANGER WILL BE PRESENT THROUGH FRIDAY.
- A COLD FRONT WILL SWEEP THROUGH WEDNESDAY AFTERNOON AND
EVENING BRINGING SCATTERED RAIN AND SNOW SHOWERS. TRAVEL
IMPACTS ARE POSSIBLE ALONG AND WEST OF THE LARAMIE RANGE.
SHORT TERM /THROUGH THURSDAY/
ISSUED AT 400 PM MST TUE DEC 16 2025
WE ARE ON TRACK FOR ANOTHER SIGNIFICANT, LONG-DURATION WIND EVENT
BEGINNING TOMORROW AND LASTING INTO FRIDAY. A POWERFUL UPPER LEVEL
LOW IS RACING INTO THE PACIFIC NORTHWEST THIS EVENING, RIDING ALONG
THE NOSE OF A 180 KNOT JET STREAK ALOFT. THIS SYSTEM WILL QUICKLY
MOVE INLAND TONIGHT, AND DEVELOP A VERY TIGHT LOW LEVEL HEIGHT
GRADIENT. THIS UPPER LEVEL SYSTEM WILL SUPPORT AN IMPRESSIVE SUB-990-
MB LEE CYCLONE OVER THE HIGH PLAINS IN NORTHEAST WYOMING OR WESTERN
SOUTH DAKOTA, WHICH WILL STRENGTHEN THE CROSS-BARRIER MSLP GRADIENT.
GRADIENTS WILL BEGIN TO SPIKE AFTER MIDNIGHT TONIGHT, AND REACH
THEIR MAXIMUM DURING THE EARLY AFTERNOON HOURS WEDNESDAY. INITIALLY,
THE DOMINANT SURFACE LOW WILL BE IN THE LEE OF THE CANADIAN ROCKIES,
ORIENTING THE GRADIENT SOUTHWEST TO NORTHEAST, AND SOUTH TO NORTH
OVER THE HIGH PLAINS. THE SURFACE TROUGH SHOULD BE TO THE WEST OF I-
25 WEDNESDAY MORNING, WITH THE EXCEPTION OF CONVERSE COUNTY. THIS
WILL GET SLOWLY PULLED EASTWARD MID MORNING INTO THE AFTERNOON,
LEADING TO A RAPID INCREASE IN WINDS ALONG AND EAST OF I-25. LREF
MEAN 700-MB WINDS EXCEED 70 KNOTS OVER THE CENTRAL AND NORTHERN
LARAMIE RANGE, WITH VERY IMPRESSIVE MSLP GRADIENTS. THE ARLINGTON TO
BORDEAUX MSLP GRADIENT MAXIMIZED AT NEARLY 8-MB. IN ADDITION,
FORECAST SOUNDINGS SHOW A FAIRLY STRONG TEMPERATURE INVERSION
SETTING UP RIGHT AROUND 700-MB, WHICH IS JUST ABOVE MOUNTAIN TOP
HEIGHT IN THE LARAMIE RANGE , WITH A WELL-MIXED UNSTABLE LAYER
BELOW. A MOUNTAIN-TOP INVERSION SETS THE STAGE FOR SIGNIFICANT
MOUNTAIN WAVE ACTIVITY WITH VERTICAL PROPAGATION WEDNESDAY. HIGH
RESOLUTION MODELS ALL SHOW MAJOR MOUNTAIN WAVE BREAKING
ACTIVITY DURING THE LATE MORNING THROUGH THE AFTERNOON, SLOWLY
PROGRESSING EASTWARD. THE WAVE FRONT WILL LIKELY HAVE A FAIRLY
SHARP CUTOFF ASSOCIATED WITH A HYDRAULIC JUMP. THE WIND
POTENTIAL FROM THE 700-MB FLOW SUGGESTS WIDESPREAD 70 TO 80 MPH
ALONG I-25 (PLUS THE I-80 WIND PRONE AREAS). SOME DOWNSLOPE
ACCELERATION ASSOCIATED WITH MOUNTAIN WAVE BREAKING WILL PROVIDE
POTENTIAL FOR A FEW ISOLATED 90+MPH GUSTS, ESPECIALLY IN PLATTE
COUNTY. OVERALL, THE WINDOW FOR STRONG WINDS WITH THIS EVENT
WILL BE QUITE A BIT SHORTER THAN OUR LAST FEW SIGNIFICANT WIND
EVENTS, BUT THE MAXIMUM GUST POTENTIAL IS SUBSTANTIAL.
THE WIND EVENT WILL BEGIN TO TRANSITION TO A MORE BORA-TYPE EVENT
BEHIND A STRONG COLD FRONT SWEEPING THROUGH WEDNESDAY AFTERNOON AND
EVENING. DEEP MOISTURE WILL RETURN TO THE CLOUD LAYER AROUND MID-
MORNING, WHICH SHOULD ALLOW OROGRAPHIC SNOW SHOWER ACTIVITY TO
RETURN TO OUR MOUNTAINS AHEAD OF THE FRONT. A WINTER WEATHER
ADVISORY HAS BEEN ISSUED FOR THE HIGHER MOUNTAINS TO COVER THIS
POTENTIAL. WHILE SNOW TOTALS ARE MARGINAL, STRONG WINDS OF 60 TO
70 MPH AND THE POTENTIAL FOR HEAVY SNOWFALL RATES PROMPTED THIS
ISSUANCE. BY AROUND 2PM, THE SURFACE FRONT WILL BEGIN TO
ENCROACH ON THE AREA, CLEARING THROUGH SIDNEY BY AROUND 7PM.
FROM ABOUT 2PM THROUGH 7PM, WE WILL NEED TO WATCH FOR RAIN AND
SNOW SHOWERS SPREADING OUT OF THE MOUNTAIN ASSOCIATED WITH
STRONG FRONTOGENESIS. THIS WILL BE OF PARTICULAR CONCERN FOR
CARBON AND ALBANY COUNTIES, WHERE FORECAST SOUNDINGS SHOW STEEP
LAPSE RATES, GOOD LOW-LEVEL MOISTURE, AND MODEST INSTABILITY IN
ADVANCE OF THE FRONT. TEMPERATURES WILL ALSO RAPIDLY DROP BELOW
FREEZING HERE, WHEREAS THOSE FURTHER EAST WILL TAKE A LITTLE
LONGER TO REACH FREEZING. WE WILL NEED TO WATCH FOR LOCALLY
HEAVY SNOW SHOWERS, WITH SOME POTENTIAL TO REACH SNOW SQUALL
CRITERIA ALONG I-80 BETWEEN CHEYENNE AND RAWLINS. OVERALL SNOW
ACCUMULATION TOTALS ARE EXPECTED TO BE MODEST, BUT THOSE UNDER A
HEAVIER SNOW BAND COULD PICK UP A QUICK INCH OR TWO, WHICH MAY
BE MORE HAZARDOUS WHEN COMBINED WITH A FLASH FREEZE.
THE COLD FRONT WILL MARK THE END OF THE 75+ MPH WIND GUST POTENTIAL,
BUT MOST OF THE AREA WILL REMAIN QUITE WINDY ALL THROUGH WEDNESDAY
NIGHT AND THURSDAY MORNING. THE POWERFUL UPPER LEVEL LOW WILL EJECT
INTO THE PLAINS OVERNIGHT. MODELS SHOW VERY STRONG FLOW WRAPPING
AROUND THE BACKSIDE OF THIS LOW, WHICH POSSIBLY COULD BE CONSIDERED
A STING JET. 700-MB WINDS OF 60 TO 80 KNOTS ARE EXPECTED OVER THE
HIGH PLAINS INTO THURSDAY MORNING AS THIS MOVES OVERHEAD. THIS IS
CERTAINLY IMPRESSIVE, BUT UNLIKELY TO BE REALIZED AT THE GROUND
SINCE THE STRONGEST WINDS MOVE OVERHEAD AT SUNRISE. IT CAN BE VERY
DIFFICULT FOR THE HIGH PLAINS TO REACH HIGH WIND CRITERIA OVERNIGHT,
BUT THERE MAY BE A BRIEF WINDOW FOR MIXING RIGHT AROUND SUNRISE
THROUGH THURSDAY MORNING BEFORE FORCING EVAPORATES BY MIDDAY. IN
ADDITION TO UPGRADING ALL EXISTING HIGH WIND WATCHES TO WARNINGS, A
NEW WATCH WAS ISSUED FOR THE CENTRAL AND SOUTHERN NEBRASKA PANHANDLE
TO COVER THE THURSDAY PHASE OF THE WIND EVENT. LOOK FOR MUCH COLDER
TEMPERATURES ACROSS THE AREA ON THURSDAY.
FIRE WEATHER WILL BE A CONCERN THROUGHOUT THIS EXTENDED WIND EVENT.
SNOW COVER IS LONG GONE OUTSIDE OF THE MOUNTAINS, LEAVING DORMANT,
DRY GRASSES. DESPITE RELATIVE HUMIDITY REMAINING ABOVE CRITICAL
THRESHOLDS, WILDFIRE STARTS IN GRASSLANDS COULD SPREAD VERY QUICKLY
IN THE STRONG WINDS ANTICIPATED.
LONG TERM /THURSDAY NIGHT THROUGH MONDAY/
ISSUED AT 400 PM MST TUE DEC 16 2025
A BROAD RIDGE STARTS TO DEVELOP OVER THE WESTERN
UNITED STATES GIVING US A WARM UP AFTER THE COLD FRONT PASSES
THROUGH ON THURSDAY. THE WINDS WILL GRADUALLY WEAKEN FRIDAY INTO
SATURDAY AS THE WEAK CLIPPER SYSTEM PUSHES EAST AND THE RIDGE AXIS
MOVES OVER THE INTERMOUNTAIN WEST. ANOTHER QUICK SHORTWAVE PASSES
THROUGH THE REGION SATURDAY MORNING AND INTO THE AFTERNOON. HOWEVER,
WITH THE CONTINUED WESTERLY FLOW THE STOUT DRY LAYER NEAR THE
SURFACE WILL LIKELY KEEP ANY PRECIPITATION CHANCES CONFINED TO THE
MOUNTAINOUS REGIONS. 700MB TEMPERATURES LOOK TO BE IN THE POSITIVES
MEANING THAT ANY PRECIPITATION THAT FALLS MAY COME DOWN AS RAIN OR A
RAIN/SNOW MIX, WHILE ONLY THE MOUNTAIN PEAKS WILL LIKELY SEE SNOW.
THESE WARMER 700MB TEMPERATURES LOOK TO REMAIN THROUGH THE WEEKEND
AND INTO THE BEGINNING OF THE WORK WEEK. THIS WARM AIRMASS COUPLED
WITH OUR WESTERLY FLOW WILL KEEP TEMPERATURES IN THE 50'S AND 60'S
FOR THE LOWER ELEVATIONS AND 40'S AND 50'S IN THE HIGHER ELEVATIONS
WEST OF I-25. THE WINDS LOOK TO TAKE A QUICK BREAK SATURDAY, BUT
WILL MAKE A RETURN SUNDAY INTO MONDAY AS A SHORTWAVE REVIVES OUR
700MB JET FOR POSSIBLE GUSTY WINDS BEFORE DIEING OFF AGAIN ON
TUESDAY.
AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/
ISSUED AT 1045 AM MST TUE DEC 16 2025
VFR CONDITIONS WILL PREVAIL THROUGH THE TAF PERIOD. A BRIEF LULL
IN WINDS LOOK LIKELY IN THE EVENING AND OVERNIGHT PERIOD.
STARTING AROUND 15Z THE WIND GUSTS SHOULD RETURN FOR MOST OF THE
SITES. LOW LEVEL WIND SHEAR WILL BE THE MAIN CONCERN FOR
MAJORITY OF THE SITES STARTING AROUND 12Z. THE WIND SHEAR LOOKS
TO FLOAT BETWEEN 45-50KTS OVER THE SOUTHEAST WYOMING TERMINALS
AND BETWEEN 35 TO 45 KNOTS OVER THE NEBRASKA TERMINALS.
CYS WATCHES/WARNINGS/ADVISORIES
WY...HIGH WIND WARNING FROM 11 AM WEDNESDAY TO 11 AM MST THURSDAY
FOR WYZ102-108.
HIGH WIND WARNING FROM 3 AM WEDNESDAY TO MIDNIGHT MST
WEDNESDAY NIGHT FOR WYZ101.
HIGH WIND WARNING FROM 5 AM WEDNESDAY TO MIDNIGHT MST
WEDNESDAY NIGHT FOR WYZ103>105-109.
HIGH WIND WARNING FROM 8 AM WEDNESDAY TO MIDNIGHT MST
WEDNESDAY NIGHT FOR WYZ106-107-113-115.
HIGH WIND WARNING FROM 3 AM WEDNESDAY TO 5 AM MST THURSDAY FOR
WYZ110.
WINTER WEATHER ADVISORY FROM 9 AM TO 6 PM MST WEDNESDAY FOR
WYZ112-114.
HIGH WIND WARNING UNTIL 5 PM MST THIS AFTERNOON FOR WYZ116-117.
HIGH WIND WARNING FROM 5 AM WEDNESDAY TO 5 AM MST THURSDAY FOR
WYZ116.
HIGH WIND WARNING FROM 8 AM WEDNESDAY TO 5 AM MST THURSDAY FOR
WYZ117.
HIGH WIND WARNING FROM 11 AM WEDNESDAY TO MIDNIGHT MST
WEDNESDAY NIGHT FOR WYZ118-119.
NE...HIGH WIND WARNING FROM 11 AM WEDNESDAY TO 11 AM MST THURSDAY
FOR NEZ002-095.
HIGH WIND WATCH FROM WEDNESDAY AFTERNOON THROUGH THURSDAY
MORNING FOR NEZ003-019>021-054-055-096.
SHORT TERM...MN
LONG TERM...MM
AVIATION...MM
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