419
FXUS65 KRIW 280440
AFDRIW
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
1040 PM MDT WED AUG 27 2025
KEY MESSAGES
- ISOLATED TO SCATTERED RAIN SHOWERS WITH VERY ISOLATED
THUNDERSTORMS WILL CONTINUE THROUGH THE AFTERNOON, ESPECIALLY
AS AN ELONGATED BAND OF PRECIPITATION MOVES INTO NORTHERN WY.
SOUTHWEST INTO SOUTHERN AND CENTRAL WY WILL HAVE A BETTER
CHANCE OF THUNDERSTORMS THIS AFTERNOON AND EARLY EVENING.
- ISOLATED SHOWERS AND THUNDERSTORMS ACROSS WESTERN AND CENTRAL
WY ON THURSDAY, WITH BETTER CHANCES ACROSS NORTHERN WY.
TEMPERATURES WILL BE ABOUT 5-8 DEGREES BELOW NORMAL.
- FRIDAY AND SATURDAY WILL CONTINUE TO BE ON THE COOL SIDE, WITH
ISOLATED SHOWERS OVER NORTH-CENTRAL WY AND SOME GUSTY WEST-
NORTHWEST WIND ACROSS SOUTHWEST INTO SOUTHERN WY.
- HIGH PRESSURE RETURNS SUNDAY AND MONDAY FOR SEASONABLE
TEMPERATURES AND MOSTLY DRY CONDITIONS WITH SOME BREEZY
AFTERNOON SOUTHWEST WINDS.
UPDATE
ISSUED AT 130 PM MDT WED AUG 27 2025
THE BAND OF PRECIPITATION EARLY THIS AFTERNOON STRETCHES FROM
NORTHWEST WY TOWARD THE SOUTHERN BIGHORN BASIN AND INTO NATRONA
COUNTY. IT IS SLOWLY LIFTING NORTHWARD AND WILL BRING ISOLATED
TO SCATTERED SHOWERS TO THE NORTHERN PART OF THE FORECAST AREA.
THE ENVIRONMENT TO THE SOUTH AND WEST OF THE BAND IS BECOMING
MORE UNSTABLE, WITH ISOLATED TO SCATTERED SHOWERS AND
THUNDERSTORMS BECOMING MORE NUMEROUS AS THE SHORTWAVE TROUGH
LIFTS NORTHEASTWARD OUT OF THE GREAT BASIN. SO FAR ALL OF THE
INDIVIDUAL CONVECTIVE CELLS ARE QUITE SMALL FOR LOTS OF POPCORN
CONVECTION. WHILE BRIEF HEAVY RAINFALL AND FREQUENT LIGHTNING
COULD BE EXPERIENCED THROUGH SUNSET, THE STORMS TODAY SHOULD
BRING WELCOME RAINFALL TO THE REGION. SPEAKING OF RAINFALL,
PRECIPITATION AMOUNTS THIS FAR HAVE RANGED FROM JUST A TRACE TO
AROUND 0.75". THE STEADY RAIN OVER MULTIPLE HOURS IS EXPECTED TO
PRIMARILY SOAK INTO THE DRY GROUND AND ONLY BRING LOCALIZED
RISES TO CREEKS AND STREAMS. THUS, AT THIS TIME, NO FLOODING
CONCERNS ARE EXPECTED.
AS THE TROUGH MOVES NORTHWARD INTO MONTANA OVERNIGHT, THE FOCUS
ON PRECIPITATION WILL STRETCH FROM YELLOWSTONE TOWARD THE
BIGHORNS MOUNTAINS. LARGER SCALE MODELS LIKE THE NAM AND GFS ARE
KEEPING THE PRECIPITATION MORE TO THE NORTH. HIRES MODELS
HOWEVER ARE INDICATING THAT THERE WILL BE ENOUGH MOISTURE AND
INSTABILITY FROM WEST-CENTRAL WY INTO THE WIND RIVER BASIN AND
NATRONA COUNTY NORTHWARD FOR ISOLATED TO SCATTERED SHOWERS AND
THUNDERSTORMS FROM LATE MORNING THROUGH SUNSET. WEST-NORTHWEST
WINDS WILL BE GUSTY FROM SOUTHWEST INTO SOUTHERN WY THURSDAY
AFTERNOON AS WELL WITH A TIGHTENED SURFACE PRESSURE GRADIENT.
PRECIPITATION TOTALS THURSDAY SHOULD BE THE HIGHEST OVER THE
NORTHWEST WY MOUNTAINS AND NORTHERN BIGHORN MOUNTAINS.
DISCUSSION
ISSUED AT 130 AM MDT WED AUG 27 2025
WV IMAGERY SHOWS THE MAIN FINGER OF THE PFJ PUSHING FURTHER
SOUTH OUT OF CANADA THAT WILL COME INTO PLAY LATER THIS WEEK AND
INTO THE WEEKEND. BROAD RIDGING INDUCED ACROSS THE CWA IS
EVIDENT WITH SOME DRY-SLOTTING THAT HAS INHIBITED MUCH OF THE
FORECASTED QPF AT THIS POINT WAY UNDER-PERFORMING WITH ALL
MODELS. IR SHOWS THE DISORGANIZATION OF THIS SYSTEM WITH THE
MAIN UPPER LEVEL LOW ACROSS WESTERN AND NORTHERN IDAHO ALREADY
MAKING A NORTH TO NORTHWESTWARD RETREAT THAT HAS KEPT MUCH OF
THE MOISTURE WEST OF THE CWA. EVEN THE MONSOONAL MOISTURE
INFLUX IS BEING STOPPED ACROSS NM AND INTO CO WITH THE UPPER
LEVEL HIGH STILL IN PLACE NOT MAKING ITS WAY EAST AS MODELS HAD
BEEN INDICATING DUE TO THE AFOREMENTIONED LOW MAKING MORE OF AN
EASTWARD PROGRESSION.
OTHERWISE, IT IS HARD TO FOLLOW ANY MODEL AT THIS POINT WITH NO
AGREEMENT WITH THE HI-RES MODELS NOR ANY OF THEM GETTING THE
ONGOING RADAR SITUATION CORRECTLY. THE HRRR IS THE ONLY ONE
REMOTELY CLOSE AND THUS WILL FOLLOW IT FOR THE DAY KNOWING QPF
AND POPS STILL NEED SLASHED. THE INDUCED RIDGE OVER THE STATE IS
DEFINITELY DRY-SLOTTING MUCH OF THE AREA WITH HOPES OF THE
ISOLATED RAIN SHOWER ACTIVITY TO BECOME MORE WIDELY SCATTERED
LATER THIS WEDNESDAY MORNING AND INTO THE AFTERNOON HOURS. MUCH
OF THE HEAVIER RAINFALL IS STAYING INTO IDAHO AND WESTERN
PORTIONS OF MT. WEST OF THE DIVIDE STILL SEE MUCH OF THE
ACTIVITY WITH AREAS TO THE EAST SEEING MORE MINIMAL CHANCES AND
QPF AMOUNTS. QPF WEST HAVE BEEN CUT TO WELL UNDER AN INCH AT
THIS POINT, AND STILL PROBABLY COULD SAY IT ISN'T ENOUGH. MODEL
INITIALIZATIONS AREN'T EVEN THAT CLOSE TO THE ONGOING SITUATION
AND HARD TO FOLLOW ANY WITH ANY TYPE OF CONFIDENCE. REGARDLESS,
AMPLE CLOUD COVER AND THE MORE MINIMAL RAIN CHANCES WILL KEEP
TEMPERATURES MORE SEASONABLE TO EVEN BELOW AVERAGE FOR THIS
TIME OF YEAR THIS AFTERNOON AND FOR THE REST OF THE WEEK INTO
SATURDAY. MODELS STILL INDICATE A WEAKER SHORTWAVE THURSDAY AND
MORESO FRIDAY, AND IF THE TREND CONTINUES, THIS WILL NOT BE
IMPACTFUL AS WELL. THE BETTER CHANCES LATER FRIDAY AND INTO
SATURDAY WILL BE FOR THE NORTHERN HALF OF THE CWA AND EAST OF
THE DIVIDE, ALTHOUGH SMALL (20-30% CONFIDENCE AND PROBABLY
LOWER AT THIS POINT). THE NORTHWEST FLOW ALOFT COMES BACK INTO
PLAY WITH A WEAKER FINGER OF THE JET IMPACTING THESE AREAS AS
THE MAIN PFJ PUSHES WELL EAST.
AS THE MAIN UPPER LEVEL LOW OFF THE PACIFIC NORTHWEST COAST
MOVES A BIT NORTHEAST, IT FILLS WITH TIME WITH DECREASING
DIVERGENCE ALOFT. THIS WILL ALLOW INDUCED RIDGING TO BUILD IN
ACROSS THE UPPER ROCKIES FROM THE BERMUDA HIGH OVER SOUTHERN NM
INTO MEXICO ALLOWING THE LOW TO BE BLOCKED FROM ANY INFLUENCE TO
THE CWA FOR THE LATER HALF OF THE WEEKEND INTO NEXT WEEK. THIS
WILL BRING A WARMING AND DRY TREND SUNDAY AND THROUGH THE LONG
TERM WITH TEMPERATURES BACK TO ABOVE AVERAGE AND MINIMAL STORM
CHANCES OUTSIDE OF THE HIGHER TERRAIN AND AIRMASS DEVELOPMENT
WITH THE WEAK UPPER LEVEL FLOW.
ALL IN ALL, HOPES ARE STILL DECENT FOR AT LEAST SOME RAINFALL
LATER TODAY AND INTO THURSDAY ESPECIALLY WEST OF THE DIVIDE.
HOWEVER, QPF AMOUNTS ARE NOT COMING TO FRUITION AT THIS POINT IN
TIME AS EVEN THE ENSEMBLE DATA HAS BEEN OUT TO LUNCH AS WELL.
AVIATION /06Z TAFS THROUGH 06Z FRIDAY/
ISSUED AT 1040 PM MDT WED AUG 27 2025
VFR CONDITIONS CURRENTLY PREVAIL ACROSS NEARLY ALL TERMINALS THE
ONLY EXCEPTION BEING KCPR DUE TO LOW CEILINGS. CONDITIONS ARE
EXPECTED TO IMPROVE FOR MOST TERMINALS THROUGH THE NIGHT AS
LINGERING SHOWERS DISSIPATE. OVERNIGHT, LOW CLOUDS AND PERHAPS EVEN
FOG ARE MAY DEVELOP AT SEVERAL TERMINALS (10 TO 20% CHANCES) WITH
GREATEST CHANCES AT KBPI, KPNA, KJAC, AND KCPR. THERE IS NOT ENOUGH
CONFIDENCE TO ADD ANY PREVAILING GROUPS AS CONFIDENCE REMAINS LOW
STILL. HOWEVER IT IS POSSIBLE TO SEE IFR TO LIFR CONDITIONS THROUGH
PARTS OF THURSDAY MORNING (10Z THROUGH 16Z TIMEFRAME). BY LATE
MORNING, MORE SIGNIFICANT CLEARING IS EXPECTED AHEAD OF THE NEXT
SHORTWAVE.
SHOWER AND THUNDERSTORM ACTIVITY INCREASES AGAIN THURSDAY AFTERNOON
WITH THIS NEXT SHORTWAVE. COVERAGE IS GOING TO BE MORE LIMITED WITH
MOST TERMINALS SEEING AROUND 30% CHANCE OF A STRAY SHOWER OR
THUNDERSTORM STARTING NEAR 19Z THURSDAY THROUGH 03Z FRIDAY. SOME
CLEARING SHOULD OCCUR BY THE END OF THE TAF PERIOD ACROSS ALL
TERMINALS. MOUNTAINS WILL LIKELY SEE PERIODS OF OBSCURATION AS
PRECIPITATION AND LOWER CLOUDS MOVE ACROSS THE AREA.
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...MCDONALD
DISCUSSION...LOWE
AVIATION...DZIEWALTOWSKI
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