399
FXUS65 KCYS 140454
AFDCYS
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
1050 PM MDT SUN SEP 13 2026
KEY MESSAGES
- TEMPERATURES WARM TODAY AND MONDAY WITH INCREASING PRECIPITATION
CHANCES.
- SEVERE WEATHER CHANCES RETURN ON TODAY, WITH MONDAY SEEING A
POTENTIAL CRITICAL FIRE WEATHER ENVIRONMENT ALONGSIDE HIGH
WINDS.
- MUCH COOLER ON TUESDAY WITH TEMPERATURES A FEW DEGREES WARMER
THROUGH THE END OF NEXT WEEK AND DAILY CHANCES OF SHOWERS AND
THUNDERSTORMS.
SHORT TERM /THROUGH TUESDAY/
ISSUED AT 240 PM MDT SUN SEP 13 2026
SCATTERED THUNDERSTORMS ARE IN STORE THIS AFTERNOON THROUGH THE
OVERNIGHT HOURS AS ANOTHER SHORTWAVE PASSES THROUGH OUR NECK OF THE
WOODS. SOME STRONG TO POSSIBLY SEVERE THUNDERSTORMS COULD DEVELOP IN
THE LATE AFTERNOON AS A SURFACE LOW MOVES NORTHEAST THROUGH OUR
FORECAST AREA. CAPE VALUES LOOK TO BE BETWEEN 500 TO 1,000 JOULES
WITH COUPLE POTENTIAL POCKETS OF 2,000 JOULES AS DEPICTED BY THE RAP
BETWEEN 3 TO 7PM. THE SYNOPTIC FORCING OF THE SURFACE LOW SHOULD
SUSTAIN THE SHOWERS AND THUNDERSTORMS THROUGH THE EVENING. HOWEVER,
IN THE MORNING WE HAVE A SUBSTANTIAL CAP TO ERODE AWAY IN THE
MORNING AND AFTERNOON BEFORE ANY STRONG TO SEVERE THUNDERSTORMS
COULD DEVELOP. IT WILL BE A LITTLE TOUGH TOO SINCE THE FORECASTED
CONVECTIVE TEMPERATURE IS IN THE MID 80'S AND THE FORECASTED HIGH
TEMPERATURE ARE EITHER AT OR BELOW THE CONVECTIVE TEMPERATURES. MOST
OF THE AREA IS STILL CAPPED WITH THE EXCEPTION OF NIOBRARA COUNTY
ACCORDING TO THE LATEST RAP MESOANALYSIS. MOST OF THE HI-RES MODELS
CONTINUE TO SHOW INITIATION AROUND 20/21Z WITH TRUE SCATTERED
THUNDERSTORM COVERAGE BY 00Z. SYNOPTIC WINDS WILL START TO PICK UP
THIS EVENING AS THE UPPER LEVEL LOW MOVES INTO EASTERN MONTANA AND
WESTERN NORTH DAKOTA. A HIGH WIND WATCH AND A RED FLAG WARNING GO
INTO EFFECT MONDAY AFTERNOON AS THE PRESSURE GRADIENT TIGHTENS AND
THE UPPER LEVEL LOW DRAGS DRIER AIR ACROSS SOUTHEAST WYOMING. RH
VALUES ARE EXPECTED TO DROP INTO THE TEENS AS THE 700MB FLOW STARTS
TO REACH 50-55 KNOTS BY MID MORNING. MOST LIKELY WINDS WILL BE
WESTERLY 20 KNOTS GUSTING 45 KNOTS BUT 53 KNOTS OR 60 MPH WIND GUSTS
WILL BE POSSIBLE IN OUR WIND PRONE AREAS HOWEVER, NOT QUITE SURE HOW
MUCH OF THAT JET WILL MIX DOWN HENCE WHY IT WAS KEPT AS A HIGH WIND
WATCH. IN-HOUSE RANDOM FOREST MODEL GUIDANCE HAS KEPT ITS 30 TO 40%
CHANCE FOR ELEVATED TO HIGH WINDS AT ARLINGTON, RAWLINS, BORDEAUX,
COLEMAN, AND NORTHERN CARBON COUNTY. WITH THESE INCREASED WESTERLY
DOWNSLOPING WINDS ON MONDAY, HIGH TEMPERATURES WERE RAISED HIGHER
THAT WHAT WAS BEING DEPICTED BY THE GLOBAL ENSEMBLES AND THE NBM.
ELEVATED DOWNSLOPING WINDS ARE GOING TO WARM US UP RATHER QUICKLY
AND MAY NEGATE THE EFFECTS OF THE COLDER AIRMASS BEING PULLED INTO
THE INTERMOUNTAIN WEST BEHIND THE COLD FRONT.
LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/
ISSUED AT 240 PM MDT SUN SEP 13 2026
TUESDAY AND INTO THE WEEKEND, THE UPPER LEVEL LOW
KEEPS MIGRATING EAST INTO THE GREAT LAKES AND HUDSON BAY REGION. THE
COUNTER CLOCKWISE CIRCULATION WILL BEGIN FILTERING COLD AIR FROM THE
ARCTIC INTO THE REGION UNDERGOING SOME WARMING/MODIFICATION AS IT
PUSHES SOUTH OVER US. 700MB TEMPERATURES WILL DROP BETWEEN 8 AND 12C
TRANSLATING DAILY SURFACE TEMPERATURES INTO THE COOLER 60'S AND
70'S AND OVERNIGHT TEMPERATURES INTO THE 40'S AND 50'S. DAILY
RAINFALL CHANCES START TO OCCUR WEDNESDAY AS A TRAIN OF LOW
PRESSURE SYSTEM SYSTEM ARE EXPECTED TO TRAVEL THROUGH THE
PACIFIC NORTHWEST OVER THE NEXT 7 DAYS. THIS PRECESSION OF LOW
PRESSURE SYSTEMS WILL PUSH THE RIDGE EASTWARD INTO THE CENTRAL
AND SOUTHERN PLAINS LEAVING THE INTERMOUNTAIN WEST SUSCEPTIBLE
TO MULTIPLE ACCOMPANIED SHORTWAVES BUT AHEAD AND FOLLOWING EACH
PROGGED LOW PRESSURE SYSTEM.
AVIATION /06Z TAFS THROUGH 06Z TUESDAY/
ISSUED AT 1050 PM MDT SUN SEP 13 2026
A PACIFIC COLD FRONT WILL GRADUALLY MOVE ACROSS SOUTHEAST WYOMING
AND WESTERN NEBRASKA LATER TONIGHT THROUGH MONDAY. EXPECT SHOWERS
AND WIDELY SCATTERED THUNDERSTORMS TO CONTINUE LATE THIS EVENING
WITH ANOTHER BAND OF SHOWERS EXPECTED ALONG THE LEADING EDGE OF THE
FRONT EARLY MONDAY MORNING. LOW CLOUDS LIKELY AND SOME FOG EXPECTED
ACROSS THE EASTERN PLAINS OF WESTERN NEBRASKA. GRADUAL CLEARING
AFTER SUNRISE MONDAY MORNING.
HAZARDS/WEATHER TRENDS: THUNDERSTORM ACTIVITY LINGERS ACROSS MOST OF
THE AREA WITH ANOTHER BAND OF SHOWERS AND THUNDERSTORMS MOVING INTO
CARBON COUNTY, IMPACTING KRWL OVER THE NEXT FEW HOURS THROUGH 07Z.
GUST UP TO 55 KNOTS ARE POSSIBLE WITH THIS LINE AS IT MOVES THROUGH
KRWL AND POSSIBLY KLAR LATER TONIGHT. OTHERWISE, EXPECT IFR TO LIFR
CIGS AND VIS FOR KAIA AND KSNY, WITH KCDR AND KBFF IN MVFR TO NEAR
IFR CIGS UNTIL 14Z. DO NOT EXPECT THESE LOW CLOUDS TO GET TO KCYS,
BUT CAN'T COMPLETELY RULE IT OUT EITHER (<5% CHANCE). COLD FRONT
WILL MOVE ACROSS THE WHOLE AREA BY LATE MONDAY AFTERNOON WITH GUSTY
WESTERLY WINDS SHIFTING INTO THE NORTH BEHIND THE FRONT.
CYS WATCHES/WARNINGS/ADVISORIES
WY...RED FLAG WARNING FROM NOON TO 8 PM MDT MONDAY FOR WYZ417>423-
427-432-433.
HIGH WIND WATCH FROM MONDAY MORNING THROUGH MONDAY AFTERNOON
FOR WYZ106-109-110.
NE...NONE.
SHORT TERM...MM
LONG TERM...MM
AVIATION...TJT
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