176
FXUS65 KCYS 251927
AFDCYS
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
127 PM MDT MON AUG 25 2025
KEY MESSAGES
- ISOLATED TO SCATTERED SHOWERS AND THUNDERSTORMS WILL OCCUR
THIS EVENING, PRODUCING GUSTY WINDS TO 50 MPH, SMALL HAIL,
AND PERIODS OF MODERATE TO HEAVY RAIN.
- PATCHY FOG IS EXPECTED TO DEVELOP LATE TOMORROW MORNING
ACROSS PORTIONS I-80 FROM LARAMIE TO SIDNEY.
- COOL AND WET PATTERN EXPECTED THROUGH FRIDAY, WITH DAILY
CHANCES FOR PRECIPITATION AND HIGHS 5 TO 15 DEGREES BELOW
AVERAGE.
SHORT TERM /THROUGH TUESDAY/
ISSUED AT 126 PM MDT MON AUG 25 2025
THE INTERMOUNTAIN WEST IS CURRENTLY SANDWICHED BETWEEN AN UPPER
LEVEL LOW OVER THE GREAT LAKES REGION AND A SHALLOW RIDGE TO OUR
SOUTHWEST. THIS WILL KEEP US IN NORTHWEST FLOW FOR THE NEXT COUPLE
OF DAYS. LOOKING AT MID-LEVEL WATER VAPOR, THE POOL OF MOISTURE IN
THE PACIFIC NORTHWEST IS BEING TRANSPORTED OVER THE INTERMOUNTAIN
WEST TO KEEP PWATS BETWEEN 0.5 AND 1 INCH ACROSS THE REGION. NAEFS
AND ECMWF ENS ARE ALSO SHOWING IVT AND PWATS IN THE 90TH TO 95TH
PERCENTILE OVER THE NEXT 24 HOURS KEEPING THE ENVIRONMENT WELL
SATURATED. THIS SATURATED ENVIRONMENT WILL KEEP THUNDERSTORM AND
STRATIFORM RAIN POTENTIAL HIGH. HOWEVER, THERE IS ONLY A COUPLE
HUNDRED JOULES OF ENERGY TO BE ABSORBED SO WHILE THERE MAY BE A
COUPLE RUMBLES OF THUNDER, SEVERE THUNDERSTORMS ARE TYPICALLY NOT
EXPECTED IN THIS MORE OF A PACIFIC NORTHWEST PATTERN. SPC
MESOANALYSIS ALSO SHOWS A LITTLE BIT OF CIN ACROSS THE REGION THAT
WOULD ALSO NEED TO BE OVERCOME. THE CURRENT CLOUD COVER AND COOL
TEMPERATURE WILL HELP US REMAIN STABLE AND THE CIN INTACT ESPECIALLY
OVER THE NEBRASKA PANHANDLE WHERE LOW STRATUS CURRENTLY PREVAILS.
MOST OF THE STORM POTENTIAL WILL DEVELOP IN THE HIGHER TERRAIN OF
WYOMING AND PUSH SOUTHEAST INTO LARAMIE COUNTY AND INTO THE STATE OF
COLORADO. THE RAP ALSO PLACES EFFECTIVE SHEAR AT AROUND 25 KNOTS
WHICH IS STRONG ENOUGH TO PRODUCE WEAK THUNDERSTORMS. DUE TO THE LOW
SHEAR, PULSY STORMS CAPABLE OF PRODUCING PEA SIZED HAIL AND WIND
GUSTS UP TO 40-50 MPH CAN'T BE RULED OUT FOR THIS EVENING. TOMORROW
MORNING THE FOG POTENTIAL REEMERGES ALONG THE I-80 CORRIDOR AND
POTENTIAL AS FAR NORTH AS SCOTTSBLUFF IN THE PANHANDLE. SO IT IS
LIKELY WITH THESE SHOWERS THAT FOG WILL BE PRESENT AGAIN TOMORROW AS
THE SHALLOW NOCTURNAL INVERSION DEVELOPS.
LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/
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 TUESDAY/
ISSUED AT 1129 AM MDT MON AUG 25 2025
SCATTERED SHOWERS AND THUNDERSTORMS WILL MAINLY AFFECT OUR
WYOMING TERMINALS BETWEEN 20Z AND 02Z. THERE IS A CHANCE THAT
KSNY MAY HAVE SHOWERS DEVELOP NEAR THEM IN THE EARLY EVENING BUT
MOST OF THE SHOWERS SHOULD STAY IN WYOMING. THERE IS A CHANCE
FOR EARLY MORNING FOG TOMORROW. WITH OUR LOW LEVEL MOISTURE AND
NOCTURNAL INVERSION MAY CONTRIBUTE TO A DAILY OCCURRENCE THIS
WEEK. HOWEVER, LOCATIONS ARE UNKNOWN AT THIS TIME. KRWL LOST
POWER OVERNIGHT SO NO AMENDMENTS WILL BE SCHEDULED AT THIS
TIME.
CYS WATCHES/WARNINGS/ADVISORIES
WY...NONE.
NE...NONE.
SHORT TERM...MM
LONG TERM...MN
AVIATION...MM
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page