311
FXUS65 KCYS 140535
AFDCYS
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
1130 PM MDT TUE OCT 13 2026
KEY MESSAGES
- COOLER TEMPERATURES WILL PREVAIL FOR THE REST OF THE WEEK WITH
WIDESPREAD SHOWERS THIS EVENING THROUGH THURSDAY MORNING.
- ACCUMULATING SNOW WILL DEVELOP IN THE HIGHER PEAKS TONIGHT,
AND THEN SPREAD TO AREAS ABOVE ABOUT 7000 FT IN ELEVATION
WEDNESDAY EVENING INTO THURSDAY MORNING.
- NEAR FREEZING TEMPERATURES ARE POSSIBLE (20 TO 40% CHANCE EAST
OF I-25) WEDNESDAY NIGHT. A GROWING SEASON-ENDING FREEZE IS
EXPECTED THURSDAY NIGHT INTO FRIDAY MORNING ACROSS THE ENTIRE
AREA.
SHORT TERM /THROUGH THURSDAY/
ISSUED AT 300 PM MDT TUE OCT 13 2026
OUR AREA IS IN THE MIDST OF A LULL IN PRECIPITATION CHANCES AS A
REGION OF DRY AIR MOVES OVERHEAD. WHILE CLOUDS ARE HANGING ON IN
PARTS OF THE NEBRASKA PANHANDLE AND INTO CONVERSE AND NIOBRARA
COUNTIES, SUNSHINE IS BREAKING THROUGH ELSEWHERE, ALLOWING FOR A
PLEASANT DAY WITH FALL-LIKE TEMPERATURES. HOWEVER, THE SPRAWLING
UPPER LEVEL LOW CURRENTLY OVER THE LAS VEGAS AREA WILL CONTINUE TO
MEANDER CLOSER TO THE AREA, BRINGING ANOTHER ROUND OF MOISTURE AND
LIFT INTO THE AREA LATER THIS AFTERNOON. ISENTROPIC LIFT KICKS UP
AGGRESSIVELY BY LATE AFTERNOON IN CARBON AND ALBANY COUNTIES, SPREAD
INTO THE I-25 CORRIDOR AND POINTS EAST THIS EVENING, AND FINALLY THE
NEBRASKA PANHANDLE AFTER MIDNIGHT. AS THE STRONG FORCING EXPANDS,
SHOWER ACTIVITY WILL SPREAD WITH IT. LOOK FOR NUMEROUS TO WIDESPREAD
SHOWERS DEVELOPING IN THE WEST AND SPREADING EAST, WITH SOME
ISOLATED EMBEDDED THUNDERSTORMS EXPECTED AS WELL. WITH ABUNDANT
MOISTURE IN THE ATMOSPHERE, RAINFALL SHOULD BE FAIRLY EFFICIENT.
MOST RAINFALL WILL BE LIGHT, BUT EXPECT PERIODS OF MODERATE TO
HEAVY RAINFALL TO OCCUR INTERMITTENTLY THROUGH THE NIGHT. SNOW
LEVELS OVERNIGHT TONIGHT WILL BE FAIRLY HIGH, AROUND 10 KFT TO
START, AND DROPPING TO AROUND 9 KFT BY MORNING.
EASTERLY UPSLOPE FLOW WILL BECOME MORE ORGANIZED OVERNIGHT. WITH A
DECENT REVERSE GRADIENT DEVELOPING, EXPECT TO SEE A WIND GUSTS IN
THE 25 TO 35 MPH RANGE IN CARBON AND ALBANY COUNTIES. WINDS WILL BE
WEAKER TO THE EAST, BUT STEADY. EXCELLENT MOISTURE ADVECTION WILL
BRING IN PLENTIFUL LOW CLOUD COVER AND UPSLOPE FOG ACROSS THE AREA
FOR WEDNESDAY MORNING. HIGH RESOLUTION MODELS ARE IN GOOD AGREEMENT
SHOWING THE AREA REMAINING LARGELY SOCKED IN FOR MOST OF THE DAY
WEDNESDAY, AT LEAST ALONG AND EAST OF THE LARAMIE RANGE. MORE BREAKS
IN THE CLOUD COVER CAN BE EXPECTED IN CARBON AND ALBANY COUNTIES
WHERE EASTERLY FLOW IS LOCALLY DOWNSLOPE. THICK CLOUD COVER WILL
KEEP TEMPERATURES COOL. THE NBM SEEMS UNREALISTICALLY WARM, SO
MAXIMUM TEMPERATURES WERE BLENDED TO THE NBM 10TH PERCENTILE AND THE
HRRR, RESULTING IN HIGHS GENERALLY IN THE 40S FOR THE ENTIRE AREA.
THE STORM SYSTEM WILL BEGIN A TRANSITION PHASE BEGINNING AROUND THE
LATE MORNING HOURS TOMORROW, BUT THERE IS SOME TIMING UNCERTAINTIES.
AS THE AXIS OF THE UPPER LEVEL LOW GETS CLOSER TO THE AREA,
ISENTROPIC LIFT ON THE LEADING EDGE OF THE SYSTEM WILL WEAKEN
SLIGHTLY. IN ADDITION, AN AREA OF DRIER AIR ABOVE 500-MB WILL MOVE
OVER THE AREA. EXPECT PRECIPITATION RATES TO DECREASE CONSIDERABLY
AS THIS OCCURS, WHICH WILL BE ROUGHLY MID MORNING WEDNESDAY TO THE
EARLY EVENING.
ONCE THE AXIS PASSES OUR AREA, WHICH LOOKS TO OCCUR SOMETIME BETWEEN
SUNSET AND MIDNIGHT WEDNESDAY EVENING, THE STORM SYSTEM WILL DEVELOP
A MORE PRONOUNCED TROWAL, WRAPPING MOISTURE BACK INTO THE AREA WITH
STRONG ISENTROPIC LIFT. ONCE THIS OCCURS, EXPECT PRECIPITATION
COVERAGE AND RATES TO INCREASE AGAIN, FILLING IN OVER MUCH OF THE
AREA. WHILE THE NEBRASKA PANHANDLE WILL PROBABLY STRUGGLE WITH
PRECIPITATION AMOUNTS DURING THE FIRST PHASE OF THE EVENT, THE AREA
SHOULD DO BETTER IN THIS PHASE, THOUGH THERE IS SOME UNCERTAINTY IN
THE EXACT LOCATION AND SPATIAL EXTENT OF THE TROWAL AND ASSOCIATED
FORCING. COLDER AIR WILL ALSO MOVE INTO THE AREA BEHIND THE TROUGH
AXIS, LEADING TO CRASHING SNOW LEVELS THROUGH THE NIGHT AND INTO
THURSDAY MORNING. CONFIDENCE IS NOW HIGH IN ACCUMULATING SNOW ABOVE
8000 FT, AND THE PROBABILITY FOR ACCUMULATING SNOW IS INCREASING AS
LOW AS 6000 FT IN ELEVATION. THUS, THE PRIMARY UNCERTAINTY ELEVATION
BAND INCLUDES BOTH LARAMIE AND CHEYENNE. PRECIPITATION WILL END
THURSDAY MORNING OR EARLY AFTERNOON AS DRY AIR MOVES INTO THE AREA
BEHIND THE STORM SYSTEM. WITH CLEARING SKIES, WINDS BECOMING LIGHT,
AND A COOL AIRMASS IN PLACE, EXPECT A WIDESPREAD FREEZE THURSDAY
NIGHT INTO FRIDAY MORNING.
MOUNTAINS: WITH ACCUMULATING SNOW LIKELY TO BEGIN TONIGHT IN THE
SNOWY RANGE, CONFIDENCE WAS HIGH ENOUGH TO ISSUE A WINTER WEATHER
ADVISORY BEGINNING AND MIDNIGHT AND CONTINUING THROUGH THURSDAY
MIDDAY. THE FIRST PHASE OF THE EVENT WILL BE MORE SHOWERY AND
INTERMITTENT THROUGH WEDNESDAY EARLY EVENING, WITH MORE
CONSISTENT SNOWFALL EXPECTED OVERNIGHT AND INTO THURSDAY
MORNING. THAT BEING SAID, HIGH END PROBABILITIES ARE ALSO
INCREASING, SUCH THAT THERE IS ABOUT A 40% CHANCE TO EXCEED 12"
IN THE HIGHER PEAKS OF THE SNOWY RANGE. THIS WILL NEED TO BE
MONITORED GOING FORWARD. DUE TO A LESS FAVORABLE UPSLOPE WIND
DIRECTION, THE SIERRA MADRE RANGE WAS NOT INCLUDED, BUT
PROBABILITIES FOR 6" OR MORE (SPREAD OVER A 36 HOUR PERIOD) ARE
AROUND 50% AT THIS TIME.
I-80 CORRIDOR: THE NEXT HIGHEST CONFIDENCE IN SNOW IMPACTS IS ALONG
THE HIGHER ELEVATIONS OF THE I-80 CORRIDOR, INCLUDING THE SUMMIT
BETWEEN LARAMIE AND CHEYENNE, AND THE ARLINGTON/ELK MOUNTAIN AREA.
HOWEVER, SNOW LEVELS WILL ONLY DROP TO THESE ELEVATIONS TOMORROW
AFTERNOON OR SO, SO WE HAVE TIME TO WAIT AND EVALUATE TRENDS FOR
ANOTHER MODEL CYCLE. PROBABILITIES FOR ADVISORY CRITERIA SNOWFALL
ARE AROUND 70% FOR BOTH ZONES, AND THERE IS A 30% CHANCE TO REACH
WARNING CRITERIA AMOUNTS. ARLINGTON AND ELK MOUNTAIN OFTEN
OVER-PERFORM DURING NORTHEASTERLY UPSLOPE FLOW EVENTS, SO
HEADLINES MAY BE NEEDED WITH LATER FORECAST UPDATES.
LARAMIE & CHEYENNE: ONCE THE TROUGH AXIS PASSES, WINDS WILL TURN
FROM NORTHEAST TO NORTH OR NORTHWEST. MODELS ARE IN GOOD AGREEMENT
SHOWING NNW WINDS IN THE LARAMIE VALLEY AS COLDER AIR IS PULLED INTO
THE SYSTEM. LREF MEDIAN 700-MB TEMPERATURES ARE AROUND -3 TO -5C
BETWEEN LARAMIE AND CHEYENNE. AT THIS TIME, LARAMIE IS LIKELY TO
FLIP OVER TO SNOW AND SEE ACCUMULATION WEDNESDAY NIGHT INTO THURSDAY
MORNING, AND CHEYENNE IS RIGHT ON THE EDGE DUE TO THE EXTREMELY
MARGINAL TEMPERATURES. LARAMIE HAS A 80% CHANCE FOR AN INCH OF SNOW,
AND APPROXIMATELY A 10% CHANCE TO EXCEED 4" PER THE LATEST NBM
PROBABILITIES. HOWEVER, THE TIMING OF THE EVENT (EARLY MORNING),
COMBINED WITH A VERY FAVORABLE SURFACE WIND DIRECTION SUGGESTS
POTENTIAL FOR A BOOM SCENARIO IN AND AROUND LARAMIE. THE HRRR SHOWS
AN EXCELLENT EXAMPLE OF THIS BOOM SCENARIO WHICH IS ALSO AROUND THE
75TH PERCENTILE OF THE ECMWF ENSEMBLE. FOR NOW, THE OFFICIAL
FORECAST IS FAIRLY CONSERVATIVE, BUT THIS SCENARIO IS PROBABLE
ENOUGH TO DISCUSS AND WATCH CLOSELY OVER THE NEXT 24 TO 36 HOURS.
ELSEWHERE: ACCUMULATING SNOW IS UNLIKELY BELOW ABOUT 5000 FT IN
ELEVATION, WITH PRECIPITATION EXPECTED TO REMAIN ALL RAIN. THIS
STORM SHOULD BRING WIDESPREAD WETTING RAINFALL TO THE ENTIRE AREA.
MOST LIKELY QPF AMOUNTS REMAIN GENERALLY BETWEEN 0.5" AND 1.0" FOR
THE MAJORITY OF THE FORECAST AREA. CONFIDENCE IN REACHING 0.5" IS
LOWEST NORTH OF A DOUGLAS TO CHADRON LINE, AND IN WESTERN CARBON
COUNTY OUTSIDE OF THE MOUNTAINS. EXPECT TO SEE SNOW MIXING IN OTHER
AREAS OF CARBON AND ALBANY COUNTIES, BUT THE PROBABILITIES FOR
IMPACTS ARE FAIRLY LOW.
LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/
ISSUED AT 300 PM MDT TUE OCT 13 2026
AFTER A POTENT, MULTI-DAY STORM EVENT, THE END OF THE WEEK AND INTO
THE START OF NEXT WEEK, WILL BE QUIET WITH A RETURN TO WARMER AND
DRIER WEATHER. ONCE THE LOW PRESSURE SYSTEM RESPONSIBLE FOR THE
AMPLE MID-WEEK MOISTURE MOVES EAST OUT OF THE AREA, UPPER-LEVEL
RIDGING WILL TAKE ITS PLACE. THE RIDGE WILL USHER IN WARMER AIR
ALOFT, ALLOWING SURFACE TEMPERATURES TO RISE. SUBSIDENCE UNDER THE
RIDGE WILL KEEP CLOUD COVER AWAY, HELPING TO AMPLIFY HIGH
TEMPERATURES DURING THE DAY. ON FRIDAY, TEMPERATURES WILL REBOUND
BACK TO SEASONABLE, WITH HIGHS REACHING THE 50S AND 60S. BY
SATURDAY, TEMPERATURES WILL BE BACK ABOVE AVERAGE AS 700 MB
TEMPERATURES REACH THE 90TH PERCENTILE OF NAEFS CLIMATOLOGY. HIGHS
EAST OF THE LARAMIE RANGE WILL REACH THE 70S, LEADING TO A WARM FALL
DAY.
THE RIDGE WILL FLATTEN OUT BRIEFLY ON SUNDAY AS A SHORTWAVE PASSES
SOUTH THROUGH THE FOUR CORNERS REGION. IMPACTS FROM THIS SHORTWAVE
WILL BE MINIMAL, WITH HIGH TEMPERATURES ONLY FALLING A FEW DEGREES
COMPARED TO SATURDAY. EXPECT A BREEZIER DAY ON SUNDAY AS WELL WITH
STRONG WEST WINDS IN THE TYPICAL SOUTHEAST WYOMING WIND PRONES. WARM
AND DRY CONDITIONS CONTINUE ONCE AGAIN INTO THE START OF THE WORK
WEEK. TEMPERATURES WILL REMAIN ABOVE AVERAGE FOR MONDAY AND TUESDAY
WITH DRY CONDITIONS EXPECTED BOTH DAYS. PRECIPITATION CHANCES BEGIN
TO INCREASE TUESDAY NIGHT AS A DEEP TROUGH PUSHES INTO WESTERN
CONUS.
AVIATION /06Z TAFS THROUGH 06Z THURSDAY/
ISSUED AT 1130 PM MDT TUE OCT 13 2026
PRIMARILY MVFR AND IFR WILL PREVAIL THROUGH THE TAF PERIOD AS
NUMEROUS SHOWERS AND PERHAPS A FEW THUNDERSTORMS ARE EXPECTED TO
OCCUR OVERNIGHT INTO TOMORROW. EXPECT MVFR CIGS OVERNIGHT FOR MOST
TERMINALS BASED ON LATEST METARS UNDER THE ENE UPSLOPE FLOW. NOT
EXPECTING MUCH IN THE WAY OF ANY VIS REDUCTIONS ASIDE FROM
UNDERNEATH ANY OF THE HEAVIER SHOWERS. HIGH-RESOLUTION ENSEMBLE
GUIDANCE CONTINUES TO SHOW IFR CIGS FOR KCYS AFTER 09Z UNDER A COLD
AIR DAMMING REGIME BANKED UP AGAINST THE LARAMIE RANGE. KLAR AND
KSNY MAY SEE SOME OF THESE IFR CIGS AS WELL BASED ON CURRENT HIGH
RES DATA. CAN EXPECT BRIEF PERIODS OF IFR TOMORROW EVENING AFTER 00Z
AS ANOTHER ROUND OF SHOWERS IS EXPECTED TO IMPACT SE WYOMING AND THE
NEBRASKA PANHANDLE.
CYS WATCHES/WARNINGS/ADVISORIES
WY...WINTER WEATHER ADVISORY FROM MIDNIGHT TONIGHT TO NOON MDT
THURSDAY FOR WYZ114.
NE...NONE.
SHORT TERM...MN
LONG TERM...SF
AVIATION...NB/TT
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