760
FXUS65 KCYS 261751
AFDCYS
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
1151 AM MDT TUE AUG 26 2025
KEY MESSAGES
- COOL AND WET AGAIN TODAY WITH AFTERNOON SHOWER AND
THUNDERSTORM CHANCES.
- FOG AND LOW CLOUDS EXPECTED ONCE AGAIN TONIGHT INTO WEDNESDAY
MORNING.
- COOL AND WET PATTERN EXPECTED THROUGH FRIDAY, WITH DAILY
CHANCES FOR PRECIPITATION AND HIGHS 5 TO 15 DEGREES BELOW
AVERAGE.
SHORT TERM /THROUGH WEDNESDAY NIGHT/
ISSUED AT 155 AM MDT TUE AUG 26 2025
MOSTLY QUIET OVERNIGHT WITH FOG AND LOW STRATUS ONCE AGAIN MAKING AN
APPEARANCE AS OF 07Z. FOG AND LOW STRATUS LIE ALONG A LINE FROM
CHEYENNE NORTHEASTWARD TOWARDS CHADRON AND POINTS EAST/SOUTHEAST.
MID- TO UPPER-LEVEL CLOUDS ARE MOVING ACROSS WESTERN PORTIONS OF THE
CWA WITH TEMPERATURES CURRENTLY IN THE LOW-50S TO LOW-60S AREA WIDE.
WINDS ARE MOSTLY LIGHT AND VARIABLE TONIGHT, WITH VISIBILITY DROPS
APPEARING IN THE NEBRASKA PANHANDLE.
NORTHWESTERLY FLOW ALOFT EXPECTED TO CONTINUE THROUGHOUT THE DAY
TUESDAY, USHERING IN COOL TEMPERATURES AND AMPLE PRECIPITATION
CHANCES. A HIGH OVER THE SOUTHERN CONUS CONTINUES TO ADVECT MORE
MONSOONAL MOISTURE INTO THE REGION. AS IS TYPICAL WITH NORTHWESTERLY
FLOW IN THIS REGION, MULTIPLE WEAK DISTURBANCES WILL PASS THROUGH
THE FLOW, ALLOWING ENOUGH RISING MOTION TO ASSIST WITH SHOWER AND
STORM DEVELOPMENT THROUGHOUT THE AFTERNOON AND EVENING HOURS
TUESDAY. 700MB TEMPERATURES REMAIN IN THE 8 TO 10C RANGE TUESDAY,
LEADING TO SURFACE HIGH TEMPERATURES IN THE LOW-70S TO LOW-80S
ACROSS THE REGION. SLIGHTLY WARMER TEMPERATURES ARE EXPECTED NEAR
THE PINE RIDGE AND NORTHERN PORTIONS OF THE CWA WITH HIGHER 700MB
TEMPERATURES PRESENT ACROSS THAT REGION. A FEW LOCATIONS MAY SEE THE
RETURN OF THE MID-80S TODAY. PRECIPITATION CHANCES RAMP UP THIS
AFTERNOON AS A 500MB DISTURBANCE PASSES OVERHEAD. EXPECTING ISOLATED
TO SCATTERED PRECIPITATION CHANCES, ESPECIALLY ACROSS THE SOUTHERN
AND WESTERN PORTION OF THE CWA, MOSTLY WEST OF I-25. SEVERE WEATHER
IS NOT EXPECTED WITH THESE SHOWERS AND STORMS, THOUGH PRECIPITABLE
WATER VALUES ARE IN THE 90TH PERCENTILE PER THE NAEFS CLIMATOLOGICAL
MEAN, SO SHOWERS THAT DO DEVELOP WILL LIKELY PRODUCE DECENT
PRECIPITATION FOR MUCH OF THESE AREAS. LOW CLOUDS AND FOG ARE LIKELY
TO DEVELOP ONCE AGAIN TONIGHT INTO EARLY WEDNESDAY MORNING GIVEN THE
EXCESS MOISTURE ACROSS THE REGION.
WEDNESDAY WILL BE SIMILAR TO TUESDAY, THOUGH A WIDESPREAD
PRECIPITATION EVENT IS EXPECTED AS UPPER-LEVEL FLOW TURNS MORE
WESTERLY TO SOUTHWESTERLY ACROSS MUCH OF THE REGION. SOUTHWESTERLY
FLOW AT 700MB AND THE SURFACE WILL LEAD TO AMPLE UPSLOPE FLOW ACROSS
THE SIERRA MADRE AND SNOWY RANGES, INCREASING PRECIPITATION CHANCES
DOWNSTREAM OF THE MOUNTAINS. A WEAK 500MB DISTURBANCE AND A WEAK
COLD FRONT AT 700MB WILL ACT TO INCREASE THE PRECIPITATION CHANCES
AND SPREAD THEM ACROSS MUCH OF THE REGION. THE 700MB COLD FRONT IS
VERY WEAK THOUGH AND WILL LIKELY ONLY DROP 700MB TEMPERATURES A
DEGREE OR TWO. THIS WILL STILL BE STRONG ENOUGH TO LEAD TO A
WIDESPREAD PRECIPITATION EVENT WEDNESDAY AFTERNOON INTO THE
OVERNIGHT HOURS AND EVEN INTO THE EARLY MORNING HOURS ON THURSDAY.
IT WILL FEEL MORE LIKE PACIFIC NORTHWEST WEATHER OVER THE NEXT
COUPLE OF DAYS AND WITH TEMPERATURES IN THE LOW-70S TO LOW-80S, A
FAIRLY NICE (THOUGH WET) DAY IS TAKING SHAPE FOR THURSDAY. DOWNSLOPE
FLOW ALONG THE PINE RIDGE WILL INCREASE TEMPERATURES IN CHADRON TO
THE MID-80S, WHEREAS THE REST OF THE REGION WILL REMAIN MUCH COOLER.
OVERALL, LOOKS TO BE A COOL, CLOUDY, AND WET PATTERN FOR THE NEXT
COUPLE OF DAYS.
LONG TERM /THURSDAY THROUGH MONDAY/
ISSUED AT 126 PM MDT MON AUG 25 2025
NO MAJOR CHANGES HAVE BEEN MADE TO THE LONG TERM FORECAST, WITH A
GENERALLY COOL AND UNSETTLED WEATHER PATTERN CONTINUING, BUT
BEGINNING TO BREAK DOWN OVER THE WEEKEND. WEDNESDAY IS EXPECTED TO
BRING THE BEST CHANCE FOR RAINFALL OF THIS WET PERIOD FOR MOST OF
THE AREA, BUT PARTICULARLY IN SOUTHEAST WYOMING. THE AXIS OF THE
STRONG RIDGE OVER THE SOUTHWEST US WIL BEGIN TO SHIFT EASTWARD WHILE
A SHORTWAVE TROUGH MOVES OVER THE TOP OF IT, BRINGING WITH IT A
PLUME OF ABUNDANT MONSOON MOISTURE. NAEFS MEAN PRECIPITABLE WATER
VALUES APPROACH THE CLIMATOLOGICAL 99TH PERCENTILE DURING THE DAY
WEDNESDAY, WITH FORECAST SOUNDINGS SHOWING NEAR SATURATION THROUGH
THE ENTIRE TROPOSPHERE. WHILE FORCING AND MOISTURE LOOK GOOD,
CONVECTIVE PARAMETERS ARE LARGELY UNIMPRESSIVE, WITH WEAK LAPSE
RATES, MODEST INSTABILITY, AND MARGINAL VERTICAL WIND SHEAR. AS A
RESULT, THIS IS EXPECTED TO MANIFEST AS WIDESPREAD SHOWERS WITH
WIDELY SCATTERED EMBEDDED THUNDERSTORMS THROUGHOUT THE DAY, EVEN
DURING THE MORNING HOURS. SEVERE WEATHER POTENTIAL LOOKS LIMITED,
BUT WE MAY SEE SOME LOCALLY HEAVY RAINFALL IF ANY INDIVIDUAL STORM
MANAGES TO TAP INTO THE LIMITED AVAILABLE INSTABILITY. FOR THURSDAY,
THE SHORTWAVE TROUGH WILL CONTINUE TO MOVE VERY SLOWLY OVER THE TOP
OF THE RIDGE, SQUASHING IT TO THE SOUTH SOMEWHAT. DRIER AIR WILL
BEGIN TO INFILTRATE OUR WESTERN AREAS (BUT PRECIPITABLE WATER WILL
STILL BE NEAR THE CLIMATOLOGICAL 90TH PERCENTILE), WHILE SLIGHTLY
COOLER TEMPERATURES WORK IN ALOFT. WE SHOULD SEE A BIT MORE
INSTABILITY THURSDAY AS A RESULT. WHILE OVERALL COVERAGE OF
PRECIPITATION ECHOES WILL PROBABLY BE LOWER THAN WEDNESDAY,
THUNDERSTORMS MAY HAVE SLIGHTLY MORE COVERAGE.
ENSEMBLE GUIDANCE DIVERGES SOMEWHAT FOR FRIDAY AND SATURDAY. SOME
MODELS HOLD A VERY DISORGANIZED TROUGH-LIKE PATTERN OVER THE
NORTHERN PLAINS AND NORTHERN ROCKIES, WHILE OTHERS EJECT THIS MORE
QUICKLY TO THE EAST AND ALLOW THE SOUTHWEST RIDGE TO RECOVER MORE
QUICKLY. THE FORMER SCENARIO REMAINS FAVORED BY THE ECMWF ENSEMBLE
SYSTEM, AND WOULD MEAN COOLER TEMPERATURE AND HIGHER PRECIPITATION
CHANCES FOR FRIDAY AND SATURDAY, WHILE THE LATTER IS FAVORED BY THE
GEFS SYSTEM AND WOULD GENERALLY BE SLIGHTLY WARMER AND CONSIDERABLY
DRIER. WITH LITTLE INDICATION ON WHICH WAY TO LEAN, THE FORECAST
INCLUDES A BLEND OF BOTH, WITH POPS GENERALLY IN THE 40 TO 60% RANGE
AT THIS LEAD TIME. MODELS CONTINUE TO SHOW A VERY DISORGANIZED UPPER
LEVEL PATTERN CONTINUING THROUGH THE WEEKEND AND INTO MONDAY, WHICH
LEADS TO AN OVERALL LOW CONFIDENCE FORECAST, BUT THERE IS LITTLE
INDICATION OF SUMMER HEAT RETURNING, DESPITE AN OVERALL DRYING TREND
BEING PROBABLE.
AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/
ISSUED AT 1151 AM MDT TUE AUG 26 2025
THE MAIN AVIATION CONCERN THIS AFTERNOON AND EVENING WILL BE
SCATTERED SHOWERS AND THUNDERSTORMS, MAINLY WEST OF THE LARAMIE
RANGE. A FEW STORMS COULD ALSO CREEP INTO THE INTERSTATE 25 CORRIDOR
THIS EVENING. STORMS COULD BRIEFLY REDUCE VISIBILITY AND CIGS
BELOW VFR CRITERIA. A BRIEF LULL IN SHOWER ACTIVITY WILL BE
POSSIBLE LATER TONIGHT BEFORE SHOWERS DEVELOP ONCE AGAIN EARLY
WEDNESDAY MORNING.
CYS WATCHES/WARNINGS/ADVISORIES
WY...NONE.
NE...NONE.
SHORT TERM...AM
LONG TERM...MN
AVIATION...SF
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page