056
FXUS65 KCYS 130525
AFDCYS
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
1125 PM MDT WED AUG 12 2026
KEY MESSAGES
- MONSOON MOISTURE HAS RETURNED TO THE AREA, INCREASING STORM
CHANCES THROUGH THE WEEKEND AND BRINGING TEMPERATURES DOWN TO
NEAR OR BELOW SEASONAL AVERAGES.
- SCATTERED TO NUMEROUS THUNDERSTORMS ARE EXPECTED WEDNESDAY.
STRONG WINDS, LARGE HAIL, AND LOCALIZED FLASH FLOODING ARE THE
PRIMARY CONCERNS.
- NUMEROUS TO WIDESPREAD SHOWERS AND THUNDERSTORMS ARE EXPECTED
THURSDAY WITH ISOLATED STRONG TO SEVERE STORMS AND FLASH
FLOODING POSSIBLE.
- A WARMING TREND EARLY NEXT WEEK MAY BRING US BACK TO NEAR
NORMAL LATE SUMMER WARMTH.
SHORT TERM /THROUGH FRIDAY NIGHT/
ISSUED AT 245 PM MDT WED AUG 12 2026
THE LONG PERIOD OF HOT AND DRY WEATHER HAS FINALLY COME TO AN END
ACROSS THE AREA AS MOISTURE RETURNS TODAY. THE UPPER LEVEL RIDGE HAS
SHIFTED EASTWARD INTO THE CENTRAL PLAINS, ALLOWING FOR MONSOON
MOISTURE TO FREELY FLOW NORTHWARD ACROSS THE FOUR CORNERS STATES AND
INTO WYOMING. A 500-MB VORT-MAX RIDING OVER THE TOP OF THE RIDGE IS
CURRENTLY VISIBLE ON GOES SATELLITE IMAGERY MOVING ACROSS NORTH
CENTRAL WYOMING, WHICH IS HELPING TO PROVIDE A BOOST TO TODAY'S
STORM CHANCES. MESOANALYSIS INDICATES THAT MUCH OF THE AREA IS STILL
UNDERNEATH A BIT OF CIN AT THIS TIME, BUT STORMS ARE ALREADY KICKING
OFF IN A SIMILARLY CAPPED ENVIRONMENT IN NORTHEAST WYOMING LIKELY
DUE TO THE STRONG FORCING. CONVECTIVE DEVELOPMENT WILL SPREAD
SOUTHWARD INTO OUR AREA SHORTLY, AND THEN EXPECT STORMS TO GROW
UPSCALE AND SPREAD NORTHEASTWARD THROUGH THE EVENING HOURS. OTHER
THAN THE AFOREMENTIONED CAPPING, CONVECTIVE PARAMETERS ARE QUITE
FAVORABLE FOR STRONG TO SEVERE THUNDERSTORMS TODAY, ESPECIALLY EAST
OF THE DRYLINE WHICH IS CURRENTLY RETREATING BACK TO THE LARAMIE
RANGE. MLCAPE RANGES FROM 1000 TO 2000 J/KG WITH AMPLE EFFECTIVE
BULK SHEAR AROUND 35 TO 40 KNOTS. AS SUCH, THE OUTLOOK FOR NUMEROUS
SHOWERS/STORMS AND ISOLATED TO SCATTERED STRONG TO SEVERE STORMS
REMAINS ON TRACK FOR THE AFTERNOON AND EVENING HOURS. LARGE HAIL AND
STRONG TO DAMAGING WINDS ARE THE PRIMARY SEVERE CONCERNS, BUT AS
EVIDENCED IN NORTHEAST WYOMING EARLIER, AN ISOLATED TORNADO CANNOT
BE RULED OUT. LOW-LEVEL ROTATION IS MOST PROMINENT IN NIOBRARA
COUNTY AT THIS TIME. IN ADDITION, THE MOISTURE CONTENT OF THE
ATMOSPHERE IS EXTREMELY HIGH TODAY. THE 1" CONTOUR FOR PRECIPITABLE
WATER EXTENDS ALL THE WAY BACK TO THE LARAMIE RANGE, WHILE OUR
EASTERN ZONES ARE AROUND 1.3 TO 1.4". WHILE STORMS SHOULD BE MOVING
ALONG AT A DECENT SPEED TODAY, THERE IS CERTAINLY POTENTIAL FOR
LOCALLY HEAVY RAINFALL, WHICH MAY LEAD TO ISOLATED FLASH FLOODING.
ONE PARTICULAR CONCERN IS THAT THE SOILS MAY BE HYDROPHOBIC IN AREAS
DUE TO THE ONGOING DROUGHT. WHILE THE SEVERE HAZARD SHOULD CONCLUDE
BY AROUND 9PM THIS EVENING, EXPECT SHOWERS AND A FEW THUNDERSTORMS
TO LINGER ACROSS THE AREA ALL THROUGH THE NIGHT AND INTO THURSDAY
MORNING.
MOISTURE WILL PEAK THURSDAY ACROSS THE AREA. EXPECT PRECIPITABLE
WATER VALUES TO HOVER AROUND THE 97.5 TO 99TH PERCENTILE OF
CLIMATOLOGY, WITH VALUES OVER 1.0" FOR MOST OF THE AREA, AND
APPROACHING 1.5" IN WESTERN NEBRASKA. ANOTHER UPPER LEVEL SHORTWAVE
WILL PULL OUT OF THE SOUTHWEST AND MOVE THROUGH THE AREA LATE IN THE
DAY ON THURSDAY, PROVIDING SOME FORCING FOR ASCENT ANS ALSO A
MECHANISM TO HELP ORGANIZE CONVECTIVE DEVELOPMENT. THE RISK FOR
SEVERE WEATHER LOOKS A LITTLE LOWER TOMORROW AS LAPSE RATES WILL BE
A MORE MODEST 6 TO 7 C/KM. SHEAR AROUND 30 TO 35 KNOTS AND SKINNY
CAPE PROFILES WILL STILL ALLOW FOR A FEW STRONG TO SEVERE
THUNDERSTORMS, BUT THE PRIMARY FOCUS STILL LOOKS LIKE FLASH
FLOODING. THERE MAY BE MULTIPLE ROUNDS OF SHOWER AND THUNDERSTORMS
THURSDAY, WITH COVERAGE EXPECTED TO BE IN THE NUMEROUS TO WIDESPREAD
CATEGORIES. THE ONE FAILURE MODE INTRODUCING FORECAST UNCERTAINTY IS
THAT WE WILL HAVE SOME DECENT CAPPING PRESENT AGAIN TOMORROW,
ESPECIALLY IN WESTERN NEBRASKA. A FEW HI-RES MODELS (E.G. 3KM NAM)
CHOKE OFF ALL CONVECTION ONCE IT RUNS INTO THE CAPPING EAST OF I-25.
OF COURSE, THAT SPECIFIC MODEL IS GENERALLY TOO AGGRESSIVE ON
CAPPING, BUT IT PRESENTS A PLAUSIBLE EXTREME SCENARIO WHERE CAPPING
DOES NOT BREAK DOWN AT ALL. HOWEVER, THE OTHER END OF THE RANGE OF
PLAUSIBLE FORECASTS WOULD SUPPORT POTENT RAINFALL AMOUNTS. THE ECMWF
EXTREME FORECAST INDEX FOR QPF IS AROUND 0.7 TO 0.8 FOR MOST OF THE
AREA, INDICATING FAIRLY GOOD CONSENSUS ON LOCALLY HEAVY RAINFALL. A
SHIFT OF TAILS AROUND 1 TO 2 INDICATES THAT A FEW ENSEMBLE MEMBERS
EXCEED THE CLIMATOLOGICAL MAXIMUM. SO, ALL TOGETHER, THERE IS MEDIUM
CONFIDENCE IN NUMEROUS THUNDERSTORMS WITH LOCALLY HEAVY RAINFALL
POTENTIAL. EXTREME RAINFALL EVENTS CANNOT BE RULED OUT, BUT THERE IS
ALSO A FAILURE MODE IN WHICH STORMS END UP MUCH LESS WIDESPREAD THAN
CURRENTLY FORECAST. WITH PLENTIFUL CLOUD COVER, EXPECT COOLER
TEMPERATURES ACROSS THE AREA, MOSTLY IN THE MID TO UPPER 70S!
LITTLE WILL CHANGE BY FRIDAY, BUT WE WILL BE PAST THE PEAK OF THE
MONSOON SURGE, AND SHOULD START TO SEE PRECIPITABLE WATER STARTING
TO GRADUALLY DECREASE. WE WILL STILL BE WELL ABOVE SEASONAL
AVERAGES, AROUND THE CLIMATOLOGICAL 90TH PERCENTILE. WE SHOULD HAVE
SOME MORE SUNSHINE FRIDAY MORNING DUE TO SUBSIDENCE BEHIND
THURSDAY'S SHORTWAVE TROUGH, WHICH SHOULD ALLOW FOR HIGHS TO CLIMB
PERHAPS AROUND 5 TO EVEN 10 DEGREES WARMER THAN THURSDAY, BUT STILL
NOT REALLY ABOVE SEASONAL AVERAGES. FRIDAY'S THUNDERSTORM COVERAGE
WILL BE A LITTLE LESS THAN THURSDAY, MORE IN THE SCATTERED CATEGORY,
BUT LOCALLY HEAVY RAINFALL AND FLASH FLOODING WILL REMAIN A
CONCERN.
LONG TERM /SATURDAY THROUGH WEDNESDAY/
ISSUED AT 245 PM MDT WED AUG 12 2026
AS THE LONG TERM PERIOD PROGRESSES, THE RIDGE STARTS FLATTENING OUT
AS A LOW APPROACHES FROM THE PNW. SHORTWAVES MOVE NORTHWARD TOWARD
OUR REGION WHICH BRINGS WIDESPREAD CHANCES FOR SHOWERS AND
THUNDERSTORMS TO OUR AREA. THIS MOISTURE IS STILL COMING INTO THE
AREA AS MONSOONAL MOISTURE. PRECIPITABLE WATER VALUES STAY AROUND
THE 90TH PERCENTILE RANGE, SLOWLY TAPERING OFF THROUGH THIS LONG
TERM PERIOD. WITH THIS PLENTIFUL MOISTURE, THERE IS HIGHER
CONFIDENCE IN PRECIPITATION EACH DAY THROUGH THIS PERIOD.
PRECIPITATION CHANCES ARE GREATEST IN THE AFTERNOON TO EVENING HOURS
THROUGH THE CWA. 700MB TEMPERATURES ARE AROUND 10-15C BRINGING US
SEASONAL DAYTIME HIGHS AND OVERNIGHT LOWS.
AVIATION /06Z TAFS THROUGH 06Z FRIDAY/
ISSUED AT 1125 PM MDT WED AUG 12 2026
DIFFICULT TAF FORECAST WITH TIMING AND PINPOINTING WHEN OR IF A
TERMINAL WILL GET IMPACTED BY SHOWERS AND/OR THUNDERSTORMS. IF
A STORM COMES NEAR OR GOES OVER A TERMINAL, EXPECT GUSTY AND
ERRATIC WINDS. WITH THE ADDED MOISTURE FROM WEDNESDAY'S STORMS,
DECREASE IN VIS IS POSSIBLE IN BR AND/OR FG AT KCYS, KBFF, KCDR,
KSNY, AND KAIA. THIS WILL BE POSSIBLE THROUGH MOST OF THE NIGHT
AND END BY SUNRISE. ADDITIONAL STORMS ARE LIKELY THURSDAY,
BRINGING INCREASED CHANCES OF THUNDERSTORMS. SINCE THE
CONVECTIVE NATURE, KEPT PROB30S OUT OF THE TAFS AND USED VCTS
DUE TO LOW CONFIDENCE.
CYS WATCHES/WARNINGS/ADVISORIES
WY...NONE.
NE...NONE.
SHORT TERM...MN
LONG TERM...ML
AVIATION...RZ
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