609
FXUS65 KCYS 162353
AFDCYS
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
553 PM MDT TUE SEP 16 2025
KEY MESSAGES
- A SLOW MOVING STORM SYSTEM WILL KEEP UNSETTLED WEATHER OVER
THE AREA THROUGH THURSDAY MORNING, WITH CHANCES FOR SCATTERED
SHOWERS AND THUNDERSTORMS AND COOLER TEMPERATURES EXPECTED.
- ISOLATED STRONG TO SEVERE THUNDERSTORMS ARE POSSIBLE THROUGH
THE EVENING HOURS.
- TEMPERATURES ARE EXPECTED TO WARM THURSDAY THROUGH THE
WEEKEND WITH SOME MINOR CHANCES FOR PRECIPITATION DURING THIS
TIME.
SHORT TERM /THROUGH WEDNESDAY NIGHT/
ISSUED AT 245 PM MDT TUE SEP 16 2025
THE PERSISTENT UPPER LEVEL LOW HAS BARELY MOVED SINCE YESTERDAY AS
IT BEGINS TO CLOSE OFF FROM THE FLOW ALOFT. GOES SATELLITE IMAGERY
SHOWS THE CIRCULATION CENTER OVER NORTH CENTRAL WYOMING WITH
MOISTURE AND SOUTHWEST FLOW APPARENT OVER MOST OF OUR AREA. THE
INITIAL RIPPLE IS ALREADY EJECTING OUT TO THE EAST OF OUR FORECAST
AREA. MORRILL AND CHEYENNE COUNTIES STILL HAVE A POTENTIAL TO SEE
SOMETHING OUT THE INITIAL ROUND. THE NEXT ROUND IS ALREADY STARTING
TO KICK OFF OVER THE HIGHER TERRAIN OF SOUTHERN WYOMING WEST OF A
POCKET OF CLEAR SKIES BETWEEN THE I-25 CORRIDOR AND THE WY/NE STATE
LINE. HOWEVER, THE CONVECTIVE ENVIRONMENT IN WYOMING IS SOMEWHAT
LESS CONDUCIVE TO STRONG TO SEVERE THUNDERSTORMS. DEWPOINTS ARE
RUNNING A LITTLE LOWER THAN FORECAST, AND INSTABILITY IS
UNIMPRESSIVE. HOWEVER, SHEAR IS FAIRLY STRONG AS THE JET MAXIMUM
ALOFT VERY SLOWLY SHIFTS EASTWARD OVER THE AREA. THE MOST POTENT
ENVIRONMENT IS PRESENT IN CHEYENNE AND MORRILL COUNTIES WHERE A
SEVERE THUNDERSTORM WATCH IS IN EFFECT THROUGH 9PM. THE MOST LIKELY
SCENARIO FOR STORM PROGRESSION THIS AFTERNOON AND EVENING IS THAT
THE CLUSTER OF STORMS MOVING INTO SOUTHERN WYOMING FROM COLORADO
GROWS UPSCALE AND TRANSLATES TO THE NORTH AND EAST. IT MAY STRUGGLE
BETWEEN THE I-25 CORRIDOR, BUT THEN SHOULD RUN INTO A MORE FAVORABLE
ENVIRONMENT IN NEBRASKA AND STRENGTHEN. THERE SHOULD BE SUFFICIENT
TIME FOR THE ATMOSPHERE TO DESTABILIZE ONCE AGAIN IN THE SOUTHERN
PANHANDLE AFTER THE CURRENT ROUND OF SHOWERS MOVES OUT. ELSEWHERE, AN
ISOLATED STRONG TO SEVERE STORM IS CERTAINLY POSSIBLE, BUT
WIDESPREAD SEVERE WEATHER IS NOT EXPECTED.
THIS STORM SYSTEM CONTINUES TO THROW FORECAST CHALLENGES AT US
THROUGH THE OVERNIGHT HOURS. THE UPPER LEVEL LOW WILL JUMP ACROSS
THE FORECAST AREA OVERNIGHT AND SETUP SOMEWHERE BETWEEN NORTHEAST
COLORADO AND SOUTHWEST SOUTH DAKOTA BY MIDDAY WEDNESDAY. ONCE THE
UPPER LEVEL LOW BEGINS TO BECOME ESTABLISHED TO OUR EAST WEDNESDAY
MORNING, IT WILL BEGIN TO DEVELOP A WRAP AROUND FLOW, AND EVENTUALLY
A MORE WELL-DEFINED TROWAL. THE OVERNIGHT PERIOD CONTINUES TO
PRESENT A LOT OF UNCERTAINTY REGARDING PRECIPITATION COVERAGE.
FORCING WILL BE TEMPORARILY WEAKER AS THE OVERRUNNING LIFT AHEAD OF
THE SYSTEM DETERIORATES. HOWEVER, THERE WILL STILL BE SOME LIFT FROM
THE TROUGH AXIS PASSING THROUGH AND EXPECTED CYCLOGENESIS. HI-RES
MODELS ARE ALL OVER THE PLACE, BUT CHANCES FOR SHOWERS (GENERALLY 30
TO 60%) ARE RETAINED IN THE FORECAST DURING THIS TRANSITION PERIOD.
MODELS ARE STARTING TO COME INTO BETTER AGREEMENT ON WHERE THINGS
WILL END UP WEDNESDAY AS THE STORM RE-ORGANIZES EAST OF THE
MOUNTAINS. THE OUTLIER ECMWF AND ITS ASSOCIATED ENSEMBLE HAS COME
INTO AGREEMENT WITH THE OTHER MODELS ON THE MORE NORTHERLY LOCATION
OF THE UPPER LEVEL LOW CENTER WITH THE 12Z MODEL SUITE, WHICH
INCREASES CONFIDENCE SOMEWHAT IN THE STRATIFORM PHASE OF THIS SYSTEM
MAINLY IMPACTING AREAS ALONG AND NORTH OF THE NORTH PLATTE RIVER.
EXPECT STRATIFORM RAINFALL TO FILL IN THROUGH THE MORNING ALONG AND
NORTH OF THE NORTH PLATTE RIVER VALLEY. THE MORE NORTHERLY POSITION
OF THE LOW CENTER WILL PULL DRIER WESTERLY FLOW INTO THE I-80
CORRIDOR. POPS WERE DROPPED CONSIDERABLY FOR THE I-80 CORRIDOR AND
POINTS SOUTHWARD WITH THIS UPDATE. SCATTERED SHOWERS AND A FEW
STORMS WILL STILL BE POSSIBLE FOR THIS AREA, BUT THE WIDESPREAD
RAINFALL IS NOW RELATIVELY UNLIKELY. IN THE MORE FAVORED AREA,
WIDESPREAD RAINFALL AMOUNTS OF NEAR 0.5" ARE THE MOST LIKELY
SCENARIO AT THIS TIME. HIGHER END SCENARIOS SHOW THE CAPABILITY OF
THIS SYSTEM TO DROP 1-2" OF LIQUID PRECIPITATION, BUT DUE TO
UNCERTAINTY IN THE STRENGTH AND POSITION OF THE TROWAL, THE MIDDLE
ROAD SCENARIO IS CURRENTLY REPRESENTED IN THE OFFICIAL FORECAST.
MOUNTAIN SNOW TOTALS WERE REDUCED WITH THIS FORECAST AREA AS THE
CURRENT EXPECTED POSITION OF THE UPPER LEVEL LOW PUTS A DRY SLOT
OVER THE HIGHER PEAKS. A DUSTING TO A FEW INCHES IS STILL POSSIBLE
MAINLY IN THE MEDICINE BOW PEAK AREA, BUT SHOULD BE CONFINED TO
AREAS ABOVE ABOUT 10,500'. LASTLY FOR WEDNESDAY, CLOUDY CONDITIONS
WILL KEEP TEMPERATURES WELL BELOW AVERAGE FOR MOST OF THE AREA.
EXPECT HIGHS IN THE 50S TO MID 60S OUTSIDE OF THE MOUNTAINS.
RAINFALL CHANCES WILL CONTINUE THROUGH WEDNESDAY NIGHT AND INTO
THURSDAY MORNING AS THE UPPER LEVEL LOW SLOWLY SPINS OVER CENTRAL
SOUTH DAKOTA. DRY AIR IS EXPECTED TO ADVECT INTO THE AREA FROM THE
NORTH BY AROUND THURSDAY MORNING, WHICH SHOULD BRING PRECIPITATION
TO AN END DESPITE THE UPPER LEVEL LOW REMAINING NEARLY
STATIONARY.
LONG TERM /THURSDAY THROUGH TUESDAY/
ISSUED AT 325 AM MDT TUE SEP 16 2025
TOWARDS THE END OF THE WORK WEEK, A STAGNANT UPPER-LEVEL LOW WILL
SLOWLY SPIN OVER THE NORTH CENTRAL PART OF THE COUNTRY, IMPACTING
THE CWA WITH MINOR PRECIPITATION CHANCES. BY THURSDAY, THIS LOW WILL
START PUSHING ITS WAY EASTWARD, LEAVING PRECIPITATION FROM THIS
SYSTEM LINGERING OVER THE CWA. INSTABILITY ACROSS THE AREA WILL BE
WEAK, SUGGESTING STRATIFORM-LIKE PRECIPITATION WITH PERHAPS A FEW
EMBEDDED RUMBLES OF THUNDER. WITH THE UPPER-LEVEL LOW SLOWLY
BEGINNING TO MOVE OUT, THURSDAY WILL ALSO MARK THE START OF A WARM
UP AS WARMER 700 MB TEMPERATURES ARE USHERED IN. HIGH TEMPERATURES
ON THURSDAY WILL BE ABOUT 5 DEGREES WARMER THAN WEDNESDAY, WITH
HIGHS IN THE 60S AND LOW 70S. TEMPERATURES WILL CONTINUE WARMING
INTO THE DAY FRIDAY, WITH MOSTLY SUNNY SKIES HELPING FACILITATE
HIGHS IN THE 70S ACROSS MOST OF THE CWA.
HEADING INTO THE WEEKEND, WARMING CONTINUES WITH HIGH TEMPERATURES
ON BOTH SATURDAY AND SUNDAY MAKING IT INTO THE 70S AND 80S. A WEAK
SHORTWAVE WILL MAKE ITS WAY ACROSS THE NORTHERN TIER OF THE COUNTRY
OVER THE WEEKEND, POTENTIALLY PROVIDING ENOUGH LIFT AND A BIT OF
MOISTURE FOR SHOWERS AND THUNDERSTORMS TO DEVELOP. ANY STORMS THAT
DO DEVELOP LOOK TO BE MAINLY CONFINED TO THE HIGH TERRAIN WITH
MINIMAL IMPACTS. ASIDE FROM PRECIPITATION CHANCES OVER THE WEEKEND,
ANOTHER WEAK DISTURBANCE MOVING DIRECTLY ACROSS THE CWA COULD
POTENTIALLY SPARK SOME STRONG TO MARGINALLY HIGH WINDS SUNDAY
AFTERNOON. 700 MB WINDS OVER THE USUAL SOUTHEAST WYOMING WIND PRONES
WILL REACH 50 KTS WITH DECENT SUBSIDENCE. GRADIENTS ARE ELEVATED
WHICH WILL LEAD TO THE INCREASE IN WIND SPEEDS, BUT CONTINUED MODEL
RUNS WILL BE NEEDED TO ASSESS WHETHER OR NOT HIGH WINDS WILL BE
POSSIBLE. DESPITE THIS, A WINDY DAY IS STILL EXPECTED ON SUNDAY.
HEADED INTO THE BEGINNING OF THE WORK WEEK, WEAK RIDGING/ZONAL FLOW
WILL LEAD TO A MILD AND DRY PATTERN. MOSTLY SUNNY SKIES AND ABOVE
AVERAGE TEMPERATURES CAN BE EXPECTED FOR MONDAY AND TUESDAY.
AVIATION /00Z TAFS THROUGH 00Z THURSDAY/
ISSUED AT 541 PM MDT TUE SEP 16 2025
THE COMPLEX STORM SYSTEM CONTINUES TO CAUSE AVIATION
DIFFICULTIES AS IT INCHES ITS WAY ACROSS THE AREA. THE FIRST
ROUND HAS MOSTLY DEPARTED, BUT SOME BACK-BUILDING NEAR KAIA OR
KSNY IS POSSIBLE FOR THE NEXT FEW HOURS. THE SECOND ROUND IS
SEEING LIGHTNING INTENSITY DECREASE, BUT WY TERMINALS WILL
CONTINUE A RISK FOR LIGHTNING, IFR VIS IN MODERATE TO HEAVY
RAINFALL, AND GUSTY WINDS THROUGH ABOUT 03 TO 05Z. CONFIDENCE IS
LOWER IN THIS REACHING NEBRASKA TERMINALS, BUT IMPACTS CANNOT BE
RULED OUT. A PROB30 GROUP WAS MAINTAINED FOR KSNY, WHICH HAS THE
BEST CHANCE TO SEE STORMS THIS EVENING.
IN THE LATE EVENING HOURS TOWARDS WEDNESDAY MORNING, THE STRONG
STORM SYSTEM WILL BEGIN TO RE-ORGANIZE TO OUR EAST. THE SPOTTY
DISORGANIZED SHOWERS OVERNIGHT WILL LIKELY CONSOLIDATE TO AN
AREA OF STRATIFORM RAINFALL IMPACTING KBFF, KAIA, AND KCDR
AROUND 09Z TO 11Z, WITH SCATTERED SHOWERS AND SOME ISOLATED
THUNDER NEAR OTHER TERMINALS. MOIST NORTHERLY FLOW WILL ALSO
LEAD TO LOWER CIGS AT MOST TERMINALS. THE BEST CHANCE FOR IFR IS
AT KSNY, BUT CAN'T BE RULED OUT AT ANY TERMINAL. ON AND OFF
RAINFALL WILL LEAD TO MVFR VIS (AND POSSIBLY BRIEF IFR) FOR MUCH
OF THE DAY WEDNESDAY, MAINLY IN THE CENTRAL/NORTHERN NE
PANHANDLE.
CYS WATCHES/WARNINGS/ADVISORIES
WY...NONE.
NE...NONE.
SHORT TERM...MN
LONG TERM...SF
AVIATION...MN
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