019
FXUS65 KCYS 130929
AFDCYS
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
329 AM MDT SAT SEP 13 2025
KEY MESSAGES
- A COLD FRONT WILL IMPACT THE AREA SATURDAY, BRINGING COOLER
TEMPERATURES THROUGH THE WEEKEND.
- WIDESPREAD RAINFALL AND SCATTERED THUNDERSTORMS FOR MOST OF
SOUTHEAST WYOMING AND WESTERN NEBRASKA SATURDAY AFTERNOON
THROUGH SUNDAY. A FEW STRONG THUNDERSTORMS POSSIBLE ACROSS
WESTERN NEBRASKA.
- RAINFALL CHANGING TO SNOW ABOVE 10000 FEET SATURDAY NIGHT.
SNOW ACCUMULATIONS UP TO 3 INCHES FOR THE HIGHER MOUNTAINS OF
SOUTHEAST WYOMING.
SHORT TERM /THROUGH MONDAY/
ISSUED AT 325 AM MDT SAT SEP 13 2025
CURRENT IR WATERVAPOR LOOP SHOWS A DISTINCT UPPER LEVEL TROUGH
ACROSS NORTHWEST WYOMING AT THIS HOUR. THE FIRST DISTURBANCE
AHEAD OF THIS TROUGH HAS MOVED NORTHEAST INTO THE DAKOTAS LATE
LAST NIGHT/EARLY THIS MORNING WITH THUNDERSTORM ACTIVITY ACROSS
THE NORTHERN PLAINS. THE NEXT DISTURBANCE, WHICH IS FORECAST TO
BECOME THE PRIMARY STORM SYSTEM, IS CURRENTLY PUSHING NORTHEAST
ACROSS THE FOUR CORNERS REGION WITH 00Z MODELS SHOWING THIS
DISTURBANCE MOVING INTO NORTHERN COLORADO AND SOUTHERN WYOMING
TODAY. THIS SYSTEM IS EXPECTED TO INTENSIFY AS IT MOVES INTO THE
HIGH PLAINS LATE SATURDAY, BRINGING THE POTENTIAL FOR
WIDESPREAD RAIN SHOWERS AND THUNDERSTORMS. A PERIOD OF UNSETTLED
WEATHER IS EXPECTED FOR MOST OF THE AREA, WITH COOLER
TEMPERATURES AND DECENT RAINFALL AMOUNTS LOOKING MORE LIKELY
THROUGH SUNDAY AFTERNOON. INCREASED POP UP TO 90 PERCENT FOR
PORTIONS OF THE AREA. HIGH RES MODELS IN PRETTY GOOD AGREEMENT,
SHOWING A BRIEF LULL IN THE PRECIPITATION THIS MORNING, BUT AS
THE SECONDARY DISTURBANCE LIFTS NORTHEAST...EXPECT SHOWERS AND
THUNDERSTORMS TO QUICKLY DEVELOP LATE SATURDAY MORNING AND
EARLY SATURDAY AFTERNOON ACROSS CARBON AND ALBANY COUNTIES. THIS
ACTIVITY IS THEN EXPECTED TO DEVELOP FURTHER EAST INTO THE I-25
CORRIDOR AND WYOMING/NEBRASKA BORDER BY LATE SATURDAY
AFTERNOON. OVERALL, EXPECT COOLER TEMPERATURES THIS AFTERNOON
AHEAD OF THE SHOWERS AND THUNDERSTORMS WITH HIGHS IN THE MID 70S
TO LOW 80S ALONG AND EAST OF THE I-25 CORRIDOR. FURTHER WEST,
TEMPERATURES WILL LIKELY REMAIN IN THE 60S WITH THE EARLIER
ONSET OF PRECIPITATION. WITH DEWPOINTS IN THE 50S EAST OF
INTERSTATE 25, CAN'T RULE OUT A FEW STRONG TO MARGINALLY SEVERE
THUNDERSTORMS. THE MOST FAVORABLE LOCATIONS WILL BE EAST OF A
KIMBALL TO CHADRON LINE WHERE MODELS CONTINUE TO SHOW SBCAPE OF
800 TO 1200 J/KG. HOWEVER, SHEAR IS UNIMPRESSIVE AND GENERALLY
BELOW 25 KNOTS.
FOR LATE SATURDAY NIGHT AND SUNDAY, ALL MODELS SHOW THE SLOW
MOVING DISTURBANCE BECOMING AN UPPER LEVEL LOW SOMEWHERE OVER
FAR EASTERN WYOMING AND WESTERN NEBRASKA. EVEN HIGH RES GUIDANCE
IS SHOWING CYCLOGENESIS OVER WEST-CENTRAL NEBRASKA AND INTO
SOUTH DAKOTA BY SUNDAY MORNING. WITH STRONG LIFT, INSTABILITY,
AND LOW LEVEL CONVERGENCE, EXPECT SHOWER ACTIVITY TO BECOME A
STEADY AND WIDESPREAD RAIN OVER THE HIGH PLAINS BY EARLY SUNDAY
MORNING. SOME EMBEDDED CONVECTION WILL LINGER THROUGH THE DAY
WHICH MAY LEAD TO LOCALLY HIGHER RAINFALL AMOUNTS. CURRENT MODEL
RUNS SHOW THIS WRAP AROUND RAINFALL TO LINGER INTO SUNDAY
AFTERNOON. IN FACT, IF THE STORM SLOWS DOWN ANY FURTHER, MAY BE
SEEING RAINFALL AND EMBEDDED THUNDERSTORMS LINGERING INTO LATE
SUNDAY EVENING BEFORE THE STORM WEAKENS. THIS SYSTEM WILL BRING
IN JUST ENOUGH COOLER AIR TO SUPPORT SNOW IN THE MOUNTAINS ABOVE
10,000 FEET. COULD SEE AROUND 3 INCHES OF SNOW FOR THE SNOWY
RANGE AREA BY NOON SUNDAY, WITH A COLD RAIN ELSEWHERE. HIGHS ON
SUNDAY WILL GENERALLY RANGE FROM THE LOW 60S TO LOW 70S.
ONCE THE STORM EXITS TO THE NORTHEAST LATE SUNDAY NIGHT AND
MONDAY, EXPECT A MUCH DRIER AIRMASS TO MOVE INTO THE HIGH
VALLEYS AND EVENTUALLY HIGH PLAINS. EVEN WITH DEWPOINTS SETTLING
INTO THE 30S, CAN'T RULE OUT ADDITIONAL SHOWERS AND
THUNDERSTORMS MONDAY AFTERNOON WITH TEMPERATURES INCREASING
BACK INTO THE 70S TO LOW 80S...AND MID 80S WELL EAST OF I-25.
LONG TERM /MONDAY NIGHT THROUGH FRIDAY/
ISSUED AT 330 AM MDT SAT SEP 13 2025
LONG RANGE FORECAST LOOKS ON TRACK, WITH ANOTHER PACIFIC UPPER
LEVEL TROUGH MOVING INTO THE FORECAST AREA LATE MONDAY. THIS
TROUGH IS FORECAST TO QUICKLY DIVES SOUTH INTO OUR CWA ON THE
BACKSIDE OF A SHORTWAVE RIDGE. SO, BY LATE MONDAY, EXPECT FLOW
ALOFT TO BECOME SOUTHWESTERLY. THIS WILL INCREASE MOISTURE ALONG
WITH THE STORM THREAT FOR TUESDAY INTO WEDNESDAY. ANOTHER PERIOD
OF COOLER TEMPERATURES ARE EXPECTED FOR THE MIDDLE OF NEXT WEEK,
BUT ENSEMBLE GUIDANCE SHOWS PRETTY LARGE TEMPERATURE SPREADS
TUESDAY AND WEDNESDAY. KEPT HIGH AND LOW TEMPERATURES A LITTLE
BELOW SEASONAL NORMS, BUT DID NOT GO QUITE AS AGGRESSIVE AS THE
ECMWF IS INDICATING. AS WE ROUND OUT THE WORK WEEK, RIDGING
ONCE AGAIN BUILDS BACK INTO THE REGION, DRYING THINGS OUT AND
LIMITING STORM POTENTIAL. AS WE ROUND OUT THE WORK WEEK,
ANOTHER RIDGE BEGINS TO PUSH INTO OUR CWA THAT WILL DECREASE THE
STORM THREAT AND BRING WARMER TEMPERATURES.
AVIATION /06Z TAFS THROUGH 06Z SUNDAY/
ISSUED AT 1150 PM MDT FRI SEP 12 2025
UNSETTLED WEATHER IS EXPECTED OVER SOUTHEAST WYOMING AND WESTERN
NEBRASKA THIS WEEKEND AS A BROAD PACIFIC UPPER LEVEL TROUGH SLOWLY
MOVES EASTWARD OVER THE REGION. PERIODS OF MODERATE TO HEAVY
RAINFALL, SCATTERED THUNDERSTORMS, AND GUSTY WINDS ARE POSSIBLE
SATURDAY THROUGH SATURDAY NIGHT.
HAZARDS/WEATHER TRENDS: VFR CONDITIONS WILL PREVAIL TONIGHT THROUGH
MOST OF SATURDAY AFTERNOON. A BAND OF RAIN SHOWERS WILL MAINLY
IMPACT WESTERN NEBRASKA EARLY THIS MORNING, BUT CONDITIONS SHOULD
REMAIN VFR. AFTER A BRIEF LULL WITH WINDS SHIFTING INTO THE NORTH AN
NORTHWEST EARLY SATURDAY, A POTENT UPPER LEVEL DISTURBANCE WILL MOVE
NEAR THE CO/WY BORDER, RESULTING IN SCATTERED TO NUMEROUS
THUNDERSTORMS WITH HEAVY RAINFALL THROUGH LATE SATURDAY
EVENING...MAINLY FOR KLAR, KCYS, AND KSNY...BUT ALSO POSSIBLE FOR
TERMINALS FURTHER NORTH LATER THAN 06Z SUNDAY. MVFR CIGS AND VIS ARE
EXPECTED, BUT WILL ADD IN PROB30 GROUPS FOR NOW SINCE TIMING IS
STILL QUESTIONABLE.
CYS WATCHES/WARNINGS/ADVISORIES
WY...NONE.
NE...NONE.
SHORT TERM...TJT
LONG TERM...TJT/RZ
AVIATION...TJT
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