329
FXUS65 KRIW 230411
AFDRIW
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
1011 PM MDT SAT AUG 22 2026
KEY MESSAGES
- WIDELY SCATTERED RAIN SHOWERS AND THUNDERSTORMS WILL CONTINUE
UNTIL MIDNIGHT. MAIN THREATS ARE LOCALLY HEAVY RAIN, WIND
GUSTS AROUND 50 MPH, AND FREQUENT LIGHTNING. SMALL HAIL IS
POSSIBLE AS WELL.
- THE CHANCE OF SHOWERS AND STORMS LINGERS THROUGH MUCH OF THE
WEEK, ALTHOUGH TODAY LOOKS THE MOST ACTIVE.
- TEMPERATURES WILL GENERALLY STAY ABOUT 5 TO 10 DEGREES ABOVE
NORMAL THIS UPCOMING WEEK.
UPDATE
ISSUED AT 1200 PM MDT SAT AUG 22 2026
NO REAL CHANGES TO THE SHORT TERM FORECAST. RAIN SHOWER ACTIVITY
BEEN NEAR SPOT ON IN RELATION TO HIRES DATA, ESPECIALLY THE
TRUSTY NAMNEST AS PER USUAL. STORM ACTIVITY HAS BEEN LIMITED TO
ABOUT NOTHING DUE TO THE CONTINUED CLOUD COVER DEPICTED ON IR.
AS A RESULT, SEVERE WEATHER IS LOOKING LESS LIKELY FOR EASTERN
COUNTIES AFTER 4PM. HOWEVER, STORM DEVELOPMENT LOOKS TO STILL
OCCUR THROUGH 8PM THIS EVENING FORMING A LINE THAT WILL PRODUCE
SOME STRONGER OUTFLOWS UP TO 50 MPH (50-60%). OTHERWISE,
INSTABILITY JUST WON'T BE THERE FOR MUCH, IF ANY, HAIL. NO
FLOODING ISSUES WITH THIS PROGRESSIVE PATTERN. STORMS AGAIN PUSH
OUT OF NORTHEASTERN IDAHO INTO YELLOWSTONE TOWARDS SUNSET FOR A
COUPLE HOURS TOWARDS MIDNIGHT BEFORE EXITING INTO MONTANA. TIME
OF DAY AND CONTINUED CLOUD COVER LIMIT THE INSTABILITY AND ANY
STRONGER STORMS. MORE ISOLATED THAN SCATTERED FOR SUNDAY
COMPARED TO SATURDAY. TEMPERATURES FOR SATURDAY AFTERNOON WILL
BE BUMPED A BIT DOWN NOT TAKING INTO ACCOUNT THE CLOUD COVER
LIMITING SOLAR RADIATION, BUT A BIT MORE SUN FOR SUNDAY. LONG
TERM FORECAST IS WHAT IT IS, NO CHANGES AT THIS TIME.
DISCUSSION
ISSUED AT 141 AM MDT SAT AUG 22 2026
THE MONSOON HAS ONCE AGAIN ARRIVED ACROSS THE AREA, I BELIEVE
THIS IS THE THIRD OR FOURTH APPEARANCE SO FAR. SO FAR, IT HAS
BEHAVED. WE DO HAVE SOME LIGHT SHOWERS ACROSS MAINLY THE WESTERN
HALF OF THE AREA BUT NOTHING HEAVY SO FAR. THE MAIN CONCERN IN
THE FORECAST WILL BE THE POTENTIAL FOR HEAVY RAIN AND POSSIBLE
STRONG THUNDERSTORMS TODAY. RIGHT NOW, IN THIS METEOROLOGISTS
OPINION, POTENTIAL IS MIXED FOR IF WE WILL SEE WIDESPREAD OF
EITHER.
IN REGARDS TO HEAVY RAIN, THE MAIN FACTOR WILL BE THE AMOUNT OF
MOISTURE IN THE ATMOSPHERE. DEWPOINTS HAVE BEEN SLOW TO RISE SO
FAR, BUT THEY SHOULD THIS AFTERNOON, RISING INTO THE 50S IN
PORTIONS OF THE BIGHORN BASIN AS WELL AS JOHNSON AND NATRONA
COUNTIES. PRECIPITABLE WATER VALUES SHOULD ALSO BE RATHER HIGH.
THE GFS, FOR EXAMPLE, HAS PRECIPITABLE WATER VALUES ABOUT 175 TO
200 PERCENT OF NORMAL. THIS HAD BEEN OVERDONE BY AROUND 15 TO
20 PERCENT THE PAST FEW EVENTS THOUGH. EVEN WITH THIS,
PRECIPITABLE WATER VALUES OVER 150 PERCENT OF NORMAL LOOK FAIRLY
LIKELY. THERE WILL ALSO BE SOME FORCING IN THE FORM OF A
SHORTWAVE MOVING IN FROM THE WEST. THIS SHOULD ENHANCE CHANCES
FOR ALL AREAS, SO EVERYONE WILL HAVE A CHANCE. THE BEST CHANCE
STILL LOOKS TO BE IN NORTHWESTERN WYOMING, GENERALLY A 1 IN 2
CHANCE, AND THERE IS DECENT MODEL AGREEMENT IN THIS. AS FOR
SEVERE THUNDERSTORMS, THERE LOOKS TO BE A DECENT AMOUNT OF
INSTABILITY. THIS IS ESPECIALLY SO IN THE FAVORED PORTIONS OF
OUR AREA, MAINLY EAST OF THE BIGHORN RANGE IN JOHNSON AND
NATRONA COUNTIES. LIFTED INDICES FALL AS LOW AS MINUS 4 TO MINUS
5 WITH CLOSE TO 1500 J/KG OF SURFACE CAPE HERE. THERE IS ALSO A
DECENT AMOUNT OF DIRECTIONAL SHEAR IN THIS AREA. THIS, PLUS THE
AMPLE MOISTURE, MAY INCREASE THE HAIL THREAT IN THIS AREA. WE
DO HAVE A MARGINAL RISK OF SEVERE WEATHER IN PORTIONS OF
JOHNSON AND NATRONA COUNTIES, AND THIS COULD BE EXPANDED
WESTWARD WITH THE 13Z UPDATE. ALL AREAS COULD HAVE A
THUNDERSTORM BUT WITH LESS INSTABILITY AND SHEAR MOST STORMS
WOULD BE SUB-SEVERE.
HOWEVER, THERE ARE SOME FACTORS AGAINST POSSIBLE HAZARDS. IN
REGARDS TO FLOODING AND THUNDERSTORMS, IT IS CLOUD COVER. MUCH
OF THE AREA, ESPECIALLY WESTERN WYOMING, IS COVERED BY CLOUDS AS
I WRITE THIS AROUND MIDNIGHT. IF IT STAYS MOSTLY CLOUDY FOR
MUCH OF THE DAY, THIS COULD LIMIT INSTABILITY SOMEWHAT AND
DECREASE THE CHANCE OF STRONGER THUNDERSTORMS. THERE WILL LIKELY
BE SOME AREAS THAT WILL BE SUNNIER THOUGH, ESPECIALLY FURTHER
EAST. AND THERE IS ONE MORE MITIGATING FACTOR FOR HEAVY RAIN AND
POSSIBLE FLOODING. WITH THE SHORTWAVE MOVING THROUGH, THERE
WILL BE SOME STEERING FLOW TODAY. IT WON'T BE STRONG, BUT MOST
AREAS WILL HAVE 15 TO 25 KNOTS AT 500 MILLIBARS WHICH SHOULD
KEEP STORMS MOVING SOMEWHAT. WE CONTINUE TO HAVE A MARGINAL
RISK OF EXCESSIVE RAINFALL, AND PERSISTENT STORMS COULD STILL
CAUSE FLOODING, BUT IT MAY DECREASE THE CHANCE SOMEWHAT. THE
SHORTWAVE SHOULD CLEAR THE AREA BY MIDNIGHT, BUT SOME SHOWERS
WILL LIKELY LINGER THROUGH THE NIGHT. AS FOR TEMPERATURES, MORE
CLOUD COVER SHOULD LOWER THEM AROUND 5 TO 8 DEGREES, BUT IT WILL
STILL BE ABOVE NORMAL FOR ALMOST ALL AREAS.
THE FORECAST FROM SUNDAY THROUGH MUCH OF NEXT WEEK LOOKS FAIRLY
SIMILAR. WE WILL REMAIN ON THE EDGE OF THE RIDGE. SOME MONSOONAL
MOISTURE WILL STICK AROUND, WITH PRECIPITABLE WATER VALUES REMAINING
ABOVE AVERAGE THROUGH MUCH OF THE PERIOD. HOWEVER, THEY DO LOOK
LOWER THAN TODAY, SO THE CHANCE OF CONVECTION SHOULD BE SOMEWHAT
LOWER. MOST GUIDANCE FAVORS WESTERN WYOMING AT THIS TIME. HOWEVER,
GIVEN THE POOR PERFORMANCE OF THE MODELS IN REGARDS TO TIMING AND
PLACEMENT OF THE SHOWERS AND STORMS, CONFIDENCE IN THE DETAILS
REMAINS LOW. TEMPERATURES WILL ALSO COOL OFF SOMEWHAT, BACK DOWN TO
NEAR TO JUST SLIGHTLY ABOVE NORMAL LEVELS FOR LATE AUGUST. THERE
CONTINUES TO BE SOME INDICATIONS OF DRIER AIR MOVING IN FOR THE
END OF NEXT WEEK OR NEXT WEEKEND, POSSIBLY SHUTTING OFF THE
MONSOON AND BRING A PERIOD OF WARM, BUT NOT REALLY HOT WEATHER
FOR THE END OF AUGUST.
AVIATION /06Z TAFS THROUGH 06Z MONDAY/
ISSUED AT 1000 PM MDT SAT AUG 22 2026
A LINE OF SHOWERS AND THUNDERSTORMS WILL CONTINUE OVER THE
WESTERN MOUNTAINS AND MOVE INTO THE CENTRAL BASINS BY THE START
OF THE TAF PERIOD. KRIW AND KLND HAVE THE GREATEST CONFIDENCE
AND HAVE ADDED PROB30 GROUPS THROUGH 09Z. ADDITIONALLY, SHOWERS
AND THUNDERSTORMS WILL IMPACT KBPI/KPNA THROUGH 08Z. SHOWERS ARE
EXPECTED TO IMPACT KCPR AND KRKS FROM 09Z TO 13Z.
SKIES WILL CLEAR, BECOMING SKC BY 15Z/16Z. WINDS WILL BEGIN TO
INCREASE AT KCPR AROUND THIS TIME, WITH GUSTS AROUND 25KT
EXPECTED THROUGH 00Z. SIMILAR WINDS WILL DEVELOP AT KRKS BY
18Z, KCOD AND KBPI BY 19Z AND KRIW BY 21Z. CONFIDENCE HAS
LOWERED FOR THUNDERSTORMS SUNDAY AFTERNOON, WITH KJAC AND KRKS
HAVING THE BEST CHANCES SO FAR. SHOWERS AND THUNDERSTORMS COULD
DEVELOP IN THE CENTRAL BASINS BY 21Z, BUT DO NOT HAVE HIGH
ENOUGH CONFIDENCE IN INCLUDING IN THE KCOD, KWRL, KLND OR KRIW
FORECASTS AT THIS TIME. ADDITIONAL SHOWERS AND THUNDERSTORMS
LOOK TO PUSH INTO SOUTHWESTERN PORTIONS AGAIN SUNDAY EVENING AND
COULD IMPACT KBPI/KPNA AND KRKS BETWEEN 03Z AND 06Z MONDAY.
PLEASE SEE THE AVIATION WEATHER CENTER AND/OR CWSU ZDV AND ZLC
FOR THE LATEST INFORMATION ON SMOKE, ICING AND TURBULENCE
FORECASTS.
RIW WATCHES/WARNINGS/ADVISORIES
NONE.
UPDATE...LOWE
DISCUSSION...HATTINGS
AVIATION...LAVOIE
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page