778
FXUS65 KCYS 130515
AFDCYS
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
1115 PM MDT MON OCT 12 2026
KEY MESSAGES
- SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS ARE EXPECTED
TONIGHT INTO TUESDAY MORNING AS A COLD FRONT MOVES IN.
- COOLER TEMPERATURES WILL PREVAIL FOR THE REST OF THE WEEK WITH
INCREASING CONFIDENCE IS WIDESPREAD RAINFALL TUESDAY EVENING
THROUGH THURSDAY MORNING.
- ACCUMULATING SNOW IS LIKELY (80% CHANCE) ABOVE 8500 FT IN
ELEVATION TUESDAY EVENING THROUGH THURSDAY MORNING.
- NEAR FREEZING TEMPERATURES ARE POSSIBLE (20 TO 40% CHANCE EAST
OF I-25) WEDNESDAY NIGHT. A GROWING SEASON-ENDING FREEZE IS
INCREASINGLY LIKELY THURSDAY NIGHT INTO FRIDAY MORNING ACROSS
THE ENTIRE AREA.
UPDATE
ISSUED AT 938 PM MDT MON OCT 12 2026
DECIDED TO GO AHEAD AND ISSUE A DENSE FOG ADVISORY UNTIL 7AM FOR
THE I-80 SUMMIT AND THE FOOTHILLS OF LARAMIE COUNTY BASED ON
CURRENT NIGHTTIME MICROPHYSICS SATELLITE IMAGERY ALONG WITH
WYDOT CAMERAS, WHICH ARE CURRENTLY SUGGESTING AREAS OF DENSE
FOG. STARTING TO SEE SIMILAR HINTS OF PATCHY, DENSE FOG ACROSS
PORTIONS OF THE PANHANDLE, HOWEVER CONFIDENCE AT THIS TIME
REMAINS LOWER, SO WILL LEAVE THIS TO THE OVERNIGHT SHIFT TO MAKE
A FINAL DECISION.
SHORT TERM /THROUGH WEDNESDAY NIGHT/
ISSUED AT 345 PM MDT MON OCT 12 2026
OUR WARM AND DRY PATTERN IS COMING TO AN END (OR RATHER, A BREAK) AS
A SPRAWLING UPPER LEVEL LOW APPROACHES THE AREA FROM THE WEST,
BRINGING WITH IT THE FIRST REAL TASTE OF FALL. ALOFT, GOES WATER
VAPOR IMAGERY SHOWS A DRY AIRMASS MOVING OVER THE HIGH PLAINS
THIS AFTERNOON, WHILE DEEPER MOISTURE IS PUSHING BACK INTO
CARBON AND ALBANY COUNTIES KICKING UP SCATTERED SHOWER AND
ISOLATED THUNDERSTORM ACTIVITY. MEANWHILE, A SURFACE COLD FRONT
IS ALREADY WORKING ITS WAY INTO THE AREA. THE BOUNDARY IS MOVING
ACROSS LARAMIE COUNTY AT THIS HOUR, BUT THE COOL AIR APPEARS TO
BE LAGGING SOMEWHAT, CURRENTLY AROUND WHEATLAND TO ALLIANCE.
EXPECT THE FRONT TO SURGE SOUTHWARD OVER THE NEXT FEW HOURS.
WITH BREEZY NORTHEAST WINDS IN PLACE, TEMPERATURES WILL DROP
QUICKLY THIS EVENING BEHIND THE FRONT. DEWPOINTS IN THE UPPER
30S TO LOWER 40S BEHIND THE FRONT WILL PROVIDE THE FLOOR FOR
TONIGHT'S LOW TEMPERATURES, BUT EXPECT PLENTY OF LOW CLOUDS AND
PATCHY FOG TO DEVELOP ALONG AND EAST OF THE LARAMIE RANGE BY
TUESDAY MORNING. THE UPPER LEVEL LOW DIGGING SOUTHWARD THIS
EVENING WILL HELP TO AMPLIFY THE DOWNSTREAM RIDGE TO OUR EAST,
ENHANCING ISENTROPIC LIFT. SHOWER ACTIVITY WILL INCREASE IN
COVERAGE OVER THE NEXT SEVERAL HOURS AS A RESULT, WITH SCATTERED
TO NUMEROUS SHOWERS CONTINUING THROUGH THE NIGHT. THE MID-LEVEL
FRONT WILL STALL AROUND CHEYENNE TO CHADRON OVERNIGHT. WARMER
AND DRIER AIR TO THE SOUTHEAST OF THIS FEATURE WILL LIMIT SHOWER
ACTIVITY THERE, BUT EXPECT HIGHER CHANCES FOR RAINFALL
OVERNIGHT ALONG AND TO THE NORTHWEST. PRECIPITABLE WATER REMAINS
VERY HIGH, AROUND THE 90TH TO EVEN 99TH PERCENTILE OF
CLIMATOLOGY, SO SHOWERS WILL BE CAPABLE OF PRODUCING LOCALLY
HEAVY RAINFALL. 700-MB TEMPERATURES LOOK TO REMAIN ABOVE 0C EVEN
ON THE COLD SIDE OF THE MID-LEVEL FRONT, SO SNOW LEVELS WILL BE
PRETTY HIGH TONIGHT (11 KFT EARLY, DROPPING TO 10 KFT BY
TUESDAY AM), CONFINING SNOW TO THE HIGHER ELEVATIONS OF THE
SNOWY AND SIERRA MADRE RANGES. BUT DO NOT BE SURPRISED TO SEE
SOME LIGHT SNOW ACCUMULATIONS ALONG BATTLE AND SNOWY RANGE
PASSES TUESDAY MORNING.
THE AXIS OF A SUBTLE MID-LEVEL SHORTWAVE WILL PASS THROUGH AROUND
DAYBREAK TUESDAY, TURNING 700-MB WINDS MORE WESTERLY AND THUS
SHUTTING OFF THE ISENTROPIC LIFT AND OVERRUNNING FORCING FOR ASCENT.
SHOWER COVERAGE SHOULD DROP OFF QUICKLY AFTER THIS OCCURS, WITH JUST
A FEW ISOLATED TO WIDELY SCATTERED SHOWERS CONTINUING THROUGH THE
DAY ON TUESDAY. TEMPERATURES WILL BE NOTICEABLY COOLER THAN TODAY
THANKS TO PLENTIFUL LOW CLOUD COVER. LOOK FOR HIGHS STUCK IN THE MID
50S TO LOWER 60S FOR MOST OF THE AREA (ALTHOUGH THIS IS ACTUALLY
VERY CLOSE TO SEASONAL AVERAGE TEMPERATURES). EXPECT A LITTLE BIT OF
MIDDAY SUNSHINE IN BETWEEN WHEN THE MORNING LOW CLOUDS BREAK AND
WHEN THE AFTERNOON MID TO UPPER LEVEL CLOUDS INCREASE. MODELS REMAIN
CONSISTENT SHOWING A STRONGER SURGE IN POSITIVE THETA-E ADVECTION
AND ISENTROPIC LIFT DEVELOPING MID AFTERNOON TUESDAY. WHILE
INSTABILITY IS PALTRY, THERE WILL BE SOME PRESENT ALONG WITH VERY
STRONG VERTICAL WIND SHEAR. THUS, A FEW ISOLATED THUNDERSTORMS ARE
EXPECTED TUESDAY AFTERNOON AND EVENING TOO. OVERNIGHT TUESDAY INTO
EARLY WEDNESDAY, THE POWERFUL UPPER LEVEL LOW WILL GRADUALLY
PROGRESS EAST AND BREAK ITSELF AWAY FROM THE NORTHERN BRANCH FLOW.
THIS WILL ALLOW SOUTHERLY MID-LEVEL WINDS TO CONTINUE IF NOT
POSSIBLY GAIN AN EASTERLY COMPONENT, CONTINUING STRONG ISENTROPIC
LIFT FOR AN EXTENDED DURATION. EXPECT NUMEROUS SHOWERS TUESDAY
EVENING TO TRANSITION MORE TO STRATIFORM RAINFALL LATE IN THE NIGHT
AND INTO WEDNESDAY MORNING. SNOW LEVELS WILL CONTINUE THEIR GRADUAL
DROP DURING THIS PERIOD, STARTING OFF AROUND 10 KFT TUESDAY EVENING,
AND DROPPING TO 9 KFT BY WEDNESDAY MORNING. WHILE THAT IS THE MOST
LIKELY LEVEL, SNOW MIXING IN AS LOW AS LARAMIE CANNOT BE RULED OUT
BY WEDNESDAY MORNING.
ABUNDANT MOISTURE, UPSLOPE FLOW, AND CONTINUED ISENTROPIC LIFT WILL
PRODUCE A CHILLY DAY ACROSS THE AREA WEDNESDAY. MOST AREAS WILL STAY
STUCK IN THE MID 40S TO LOWER 50S WITH WIDESPREAD FOG ALONG AND WELL
TO THE EAST OF THE CREST OF AREA MOUNTAIN RANGES. LOW ELEVATION RAIN
AND HIGH ELEVATION SNOW WILL CONTINUE THROUGH THE DAY WEDNESDAY, BUT
RATES MAY BE INTERMITTENT. SINCE UPSLOPE LIFT WILL BE A
CONTRIBUTING FACTOR, RATES WILL LIKELY DECREASE THE FURTHER EAST
OF THE LARAMIE RANGE ONE GOES. THE BIGGEST REMAINING QUESTION
WITH THIS EVENT IS WEDNESDAY NIGHT INTO THURSDAY MORNING.
ENSEMBLES REMAIN SPLIT CONCERNING HOW EFFECTIVELY THE PRIMARY
UPPER LEVEL LOW WILL MANAGE TO CLOSE OFF FROM THE FLOW TO THE
NORTH. IF THE SYSTEM CLOSES OFF FULLY (E.G. THE VAST MAJORITY OF
ECMWF ENSEMBLE MEMBERS), THE STORM WOULD BE ABLE TO WRAP
PLENTIFUL MOISTURE AND ISENTROPIC ASCENT AROUND TO ITS NORTHWEST
FLANK, ALLOWING GOOD PRECIPITATION RATES TO CONTINUE THROUGH
THE NIGHT WEDNESDAY NIGHT AND INTO THURSDAY. ANOTHER CLUSTER OF
ENSEMBLE MEMBERS, MADE UP OF A MAJORITY OF GEFS MEMBERS SHOWS
THE UPPER LEVEL LOW STRUGGLING TO FULLY CLOSE OFF. AS A RESULT,
MID-LEVEL WINDS NEVER GO EASTERLY, AND THE WRAP- AROUND MOISTURE
AND LIFT IS SIGNIFICANTLY LESS IMPRESSIVE. IN THIS SCENARIO,
PRECIPITATION AMOUNTS WOULD BE GREATLY REDUCED. DUE TO THIS
UNCERTAINTY, POPS WERE HELD AT AROUND 60 TO 75% WEDNESDAY NIGHT
INTO THURSDAY AND QPF WAS ADJUSTED SLIGHTLY DOWNWARD. SNOW
LEVELS WILL CONTINUE TO DROP WEDNESDAY NIGHT INTO THURSDAY
MORNING. MOST LIKELY SNOW LEVELS END UP AROUND 7500 TO 8000 FT,
BUT NUMEROUS ENSEMBLE MEMBERS (MAINLY FROM THE CLUSTER THAT
FULLY CLOSES OFF THE STORM SYSTEM) HAVE SNOW LEVELS DROPPING AS
LOW AS 6000 FT. DUE TO THIS POTENTIAL, A SLIGHT CHANCE FOR SNOW
WAS INTRODUCED WEDNESDAY NIGHT AND THURSDAY MORNING TO CHEYENNE
AND LARAMIE.
LASTLY, WE'LL TAKE A LOOK AT TOTAL QPF EXPECTATIONS FOR THE ENTIRE
EVENT COMBINED. ENSEMBLE SYSTEMS ARE GENERALLY CLOSELY CLUSTERED TO
OTHER MEMBERS OF THE SAME SYSTEM, BUT ARE STILL DIVERGENT BETWEEN
DIFFERENT ENSEMBLE SYSTEMS. THE OFFICIAL FORECAST IS GENERALLY CLOSE
TO THE GEFS MEDIAN, WHICH IS THE SYSTEM IN ROUGHLY THE MIDDLE OF THE
GRAND ENSEMBLE. THE GEFS AI SYSTEM MEDIAN IS A BIT LOWER, AND THE
ECMWF ENSEMBLE IS A BIT HIGHER. NBM GUIDANCE STILL APPEARS TO BE
SHOWING UP ON THE HIGHER END OF THE ENSEMBLE ENVELOPE, SO QPF WAS
BLENDED TO A SMALL CONTRIBUTION OF THE 10TH PERCENTILE TO BRING
AMOUNTS MORE IN LINE WITH THE LREF MEDIAN. THIS RESULTS IN STORM
TOTAL QPF AROUND 0.3 TO 0.6" EAST OF A DOUGLAS TO KIMBALL LINE, AND
0.5" AND 1.0" ALONG AND WEST OF I-25. ACCUMULATING SNOW IS
INCREASINGLY LIKELY ABOVE 8500 FT IN ELEVATION. THE MOST LIKELY
SCENARIO AT THIS TIME WOULD PRODUCE WINTER WEATHER ADVISORY AMOUNTS
IN THE SNOWY RANGE (80% PROBABILITY OF 6" OR MORE), BUT WE ARE A
LITTLE TOO FAR OUT TO ISSUE ANY PRODUCTS AT THIS TIME.
LONG TERM /THURSDAY THROUGH MONDAY/
ISSUED AT 345 PM MDT MON OCT 12 2026
THE LONG TERM WILL BE STARTING OFF QUITE INTERESTING ON THE BACK
SIDE OF OF THE CUTOFF LOW THAT WILL BRING WIDESPREAD
PRECIPITATION TO THE REGION AND COOLER AIR AS WELL. THURSDAY
MORNING WE'LL SEE WIDESPREAD PRECIPITATION STILL ONGOING, WITH
MOSTLY RAIN FOR OUR LOWER ELEVATION ZONES, RAIN/SNOW TO PURE
SNOW FOR OUR HIGHER ELEVATIONS, AND LIKELY SNOW IN THE
MOUNTAINS. OF NOTE THOUGH WILL BE MORNING TEMPERATURES AND THEIR
EFFECT ON OUR MID TO LOWER ELEVATION LOCATIONS. WHILE WE'RE NOT
EXPECTING THE FIRST WIDESPREAD WINTER STORM OF THE SEASON QUITE
THIS EARLY, SOME ENSEMBLES AND DETERMINISTIC GUIDANCE ARE
STARTING TO HINT THAT WE MAY GET TEMPERATURES COLD ENOUGH
SPILLING JUST OFF OF THE HIGH TERRAIN THAT WE COULD SEE SOME
NEAR SURFACE WINTRY MIX, POSSIBLY OFF THE LARAMIE SUMMIT AND
EVEN COMING DOWN INTO THE CHEYENNE AREA. EVEN IF THIS DOES OCCUR
THOUGH, BEING THE FIRST COLD SPELL OF THE YEAR COMBINED WITH
WARM GROUND TEMPERATURES, ACCUMULATIONS ARE NOT LIKELY OR WILL
MELT VERY QUICKLY, BUT THE CHANCE IS THERE. NONETHELESS, MORNING
SNOW WILL LIKELY BE ONGOING AT THE LARAMIE SUMMIT AND FOR BOTH
THE SIERRA-MADRES AND SNOWIES, BUT QPF WILL BE QUICKLY DWINDLING
AND ACCUMULATIONS WILL BE LESSENING BY THE EARLY AFTERNOON.
OTHERWISE EXPECT A BREEZY DAY, PARTICULARLY EAST OF THE I-25
CORRIDOR THIS TIME, WITH TEMPERATURES STRUGGLING TO MAKE IT OUT
OF THE 40'S TO MID 50'S THANKS TO THE LINGERING COLD AIR AND
CLOUD COVER.
THAT SHOULD BEGIN TO CHANGE INTO FRIDAY MORNING AS CLOUDS WILL
BEGIN MOVING OUT OF THE REGION AND HIGH PRESSURE RIDGING STARTS
TO OVERTAKE AS WE MOVE INTO THE WEEKEND. AT FIRST THOUGH THIS
WILL HAVE A COOLING EFFECT OVERNIGHT, AND THE CURRENT FORECAST
CALLS FOR ALL ZONES TO REACH FREEZING OR BELOW. MANY ZONES
COULD SEE HARD FREEZE CONDITIONS AS WELL, AND IT'S BECOMING
MORE AND MORE LIKELY THAT FREEZE PRODUCTS WILL BE NECESSARY. THE
NBM INDICATES A 30-100% PROBABILITY OF MORNING LOWS BELOW
FREEZING, WITH THE "WARMEST" LOCATIONS AND LOWEST PROBABILITIES
AROUND WHEATLAND AND THE NORTHERN NEBRASKA PANHANDLE.
TEMPERATURES BEGIN TO REBOUND INTO THE AFTERNOON, WITH HIGHS IN
THE 50'S TO NEAR 60 FOR THE DAY. FOLLOWING THIS WE'LL CONTINUE
TO SEE A WARMING TREND WITH TEMPERATURES BACK AROUND 10 DEGREES
ABOVE NORMAL AS THE 60'S AND 70'S RETURN UNDER STAGNANT HIGH
PRESSURE RIDGING. A CUTOFF UPPER LEVEL LOW ALONG THE BAJA
PENINSULA IN MEXICO SHOULD HELP TO STAVE OFF EVEN STRONGER
RIDGING FROM BUILDING IN, BUT IT WILL CONTINUE TO PROMOTE THE
RETURN OF ABOVE NORMAL TEMPERATURES NONETHELESS. PRESSURE
GRADIENTS MAY STRENGTHEN ENOUGH ON SATURDAY TO BRING A HIGH WIND
EVENT FOR OUR WESTERN ZONES, WITH IN HOUSE GUIDANCE ALREADY
STARTING TO SPARK A 40% PROBABILITY FOR THE BORDEAUX AREA, AND
AROUND A 20-30% PROBABILITY FOR OUR OTHER WIND PRONE LOCATIONS.
THIS MAY BE THE MOST NOTEWORTHY FORECAST ELEMENT AS WE MOVE INTO
NEXT WEEKEND, WITH AN OTHERWISE QUIET AND PLEASANT FORECAST ON
TAP.
AVIATION /06Z TAFS THROUGH 06Z WEDNESDAY/
ISSUED AT 1114 PM MDT MON OCT 12 2026
LOW CEILINGS HAVE MOVED IN TO NEARLY ALL TERMINALS ALONG AND
EAST OF THE LARAMIE RANGE, INCLUDING KCYS, KBFF, KCDR, AND KSNY
WITH KAIA EXPECTED TO FOLLOW SOON. LOW CEILINGS SHOULD REMAIN IN
PLACE THROUGHOUT THE OVERNIGHT HOURS WITH MINIMAL IMPROVEMENTS.
WITH ADDITIONAL MOISTURE IN THE REGION, PATCHY FOG CANNOT BE
RULED OUT AT THESE SAME TERMINALS, THOUGH CONFIDENCE IS QUITE
LOW. CLOUD START TO LIFT BY MID-MORNING HOURS. KLAR AND KRWL MAY
SEE LOWER CEILINGS, BUT LOOK TO REMAIN JUST ABOVE MVFR CATEGORY.
GUSTY WINDS WILL PERSIST AT KRWL OVERNIGHT WITH KLAR SEEING
LIGHTER, VARIABLE WINDS.
CYS WATCHES/WARNINGS/ADVISORIES
WY...DENSE FOG ADVISORY UNTIL 7 AM MDT TUESDAY FOR WYZ116-117.
NE...NONE.
UPDATE...NB
SHORT TERM...MN
LONG TERM...CG
AVIATION...AM
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