746
FXUS65 KRIW 281953
AFDRIW
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
153 PM MDT THU MAY 28 2026
KEY MESSAGES
- SOUTH-SOUTHEAST FLOW CONTINUES TO BRING CLOUDS OVER MOST OF
WESTERN AND CENTRAL WY TODAY UNDER VERY WARM AND BREEZY
CONDITIONS. AFTERNOON HIGH TEMPS WILL REACH THE LOW 80S TO LOW
90S IN THE LOWER ELEVATIONS (ABOUT 15-15 DEGREES ABOVE
NORMAL). ISOLATED SHOWERS AND THUNDERSTORMS ARE POSSIBLE AGAIN
THIS AFTERNOON FROM CASPER MOUNTAIN NORTHWARD TO THE BIGHORN
MOUNTAINS, AS WELL AS FROM DUBOIS NORTHWARD INTO THE
ABSAROKAS, CODY AREA, AND YNP.
- SIMILAR CONDITIONS WITH VERY WARM TEMPS AND BREEZY SOUTH WINDS
ARE EXPECTED AGAIN ON FRIDAY, THOUGH SOUTHWEST WY WILL SEE
INCREASING CLOUDS AND COOLER TEMPERATURES LATE IN THE
AFTERNOON AND EVENING DUE TO A STORM SYSTEM APPROACHING FROM
THE SOUTHWEST.
- A WEATHER SYSTEM APPROACHES FRIDAY NIGHT INTO SATURDAY MORNING
WITH A GOOD CHANCE FOR SHOWERS AND ISOLATED THUNDERSTORMS
ACROSS ALL OF WESTERN AND CENTRAL WY ON SATURDAY. THE HEAVIEST
PRECIPITATION LOOKS TO FALL IN WESTERN WYOMING AND OVER THE
MOUNTAINS, BUT EXACT AMOUNTS ARE STILL UNCERTAIN. TEMPERATURES
SHOULD COOL TO THE UPPER 50S ACROSS SOUTHWEST WY AND 70S
ACROSS NORTH-CENTRAL WY ON SATURDAY, WITH BELOW NORMAL
TEMPERATURES REMAINING THROUGH MONDAY.
- ELEVATIONS ABOVE 9000 FEET MAY SEE ACCUMULATING SNOW OVER THE
WEEKEND, WITH THE HIGHEST AMOUNTS IN THE TETONS, CENTRAL TO
NORTHERN WIND RIVERS, AND SOUTHERN ABSAROKAS. YNP COULD SEE
AROUND AN INCH OF PRECIPITATION OVER THE WEEKEND AS WELL.
UPDATE
ISSUED AT 150 PM MDT THU MAY 28 2026
THE STRONG UPPER-LEVEL LOW CONTINUES TO SPIN OVER NORTHERN
CALIFORNIA AND NORTHWEST NEVADA TODAY. THIS PATTERN IS BRINGING
SOUTH-SOUTHEAST MID-LEVEL FLOW TO WYOMING, WITH INCREASED
MOISTURE EAST OF THE CONTINENTAL DIVIDE. AS EXPECTED, SHOWERS
AND THUNDERSTORMS HAVE ALREADY DEVELOPED EARLY THIS AFTERNOON
OVER THE NORTHERN ABSAROKAS NEAR CODY, AS WELL AS OVER AND
AROUND THE BIGHORN MOUNTAINS. ADDITIONAL ISOLATED STORMS ARE
LIKELY AROUND YELLOWSTONE (NORTHWEST WY) AND FROM THE CASPER
MOUNTAIN AREA NORTHWARD INTO JOHNSON COUNTY. THESE STORMS WILL
SLOWLY MOVE NORTH-NORTHEAST WITH BRIEF HEAVY RAIN, SMALL HAIL,
AND GUSTY OUTFLOW AROUND 40-45 MPH THE PRIMARY THREATS. VERY DRY
AIR HAS MOVED INTO SOUTHWEST WY EARLY THIS AFTERNOON TOO WITH
THE SOUTHERLY SURFACE FLOW AND BOUNDARY LAYER MIXING, AND WILL
PUSH SLOWLY NORTHWARD THROUGH THE AFTERNOON AS SOMEWHAT OF A
DRYLINE DEVELOPS FROM SE TO NW ACROSS THE AREA. THE 19Z SPC
MESOANALYSIS INDICATES A POTENTIAL OF 500-1000 J/KG CAPE FOR
THESE AREAS. AROUND SUNSET AS THE BOUNDARY LAYER FORCING
RELAXES AND BREEZY/GUSTY WINDS DIMINISH, CAMS ARE SHOWING
EASTERLY FLOW MOVING INTO CENTRAL WY FROM THE HIGH-BASED
CONVECTION TO THE EAST.
ON FRIDAY, THE UPPER-LEVEL LOW IS FORECAST TO MOVE INTO NEVADA
AND BECOME SOMEWHAT NEGATIVELY TILTED. DRY WARM SOUTHERLY FLOW
WILL AGAIN OCCUR OVER WESTERN AND CENTRAL WY WITH HUMIDITIES
DROPPING TO AROUND 10 PERCENT FOR MUCH OF THE LOWER ELEVATIONS
WITH WIND GUSTS OF 20-25 MPH. THIS WILL BRING ELEVATED FIRE
WEATHER CONDITIONS TO WESTERN AND CENTRAL WY. MODEL GUIDANCE IS
AGAIN SHOWING ISOLATED SHOWERS OVER THE NW WY MOUNTAINS,
BIGHORNS, AND THE CASPER MOUNTAIN AREA. BOTH THE HRRR AND RRFS
ARE SHOWING "DECENT" CONVECTIVE OVER THE CASPER AREA LATE IN THE
AFTERNOON FOR SOME POTENTIAL OUTFLOW WIND GUSTS OF 40-55 MPH.
WILL STOP THIS UPDATE AT MIDNIGHT FRIDAY NIGHT AS THE UPPER-
LEVEL LOW THEN SWINGS INTO NORTHERN UTAH AND STARTS AN
INTERESTING 48-HOUR PERIOD OF WEATHER FOR THE WEEKEND.
DISCUSSION
ISSUED AT 1238 AM MDT THU MAY 28 2026
WE CONTINUE TO HAVE THE TWO MAIN PLAYERS IN OUR WEATHER THIS
MORNING. IN THE RIGHT (EAST) WE HAVE A RIDGE OVER THE PLAINS STATES.
AND IN THE LEFT (WEST) CORNER WE HAVE A BOWLING BALL, AKA A CLOSED
LOW THAT HAS BEEN CUT OFF FOR A FEW DAYS OVER CALIFORNIA AND NEVADA,
JUST MEANDERING A BIT FROM TIME TO TIME. THE TREND FOR DAILY
CONVECTION HAS BEEN DOWNWARD. THE WITH HEIGHTS CONTINUING TO BUILD,
IT WILL LIKELY REACH A MINIMUM TODAY. MUCH DRIER AIR WILL CONTINUE
TO MOVE EASTWARD, WITH BELOW A HALF AN INCH OR PRECIPITABLE WATER
COVERING MOST OF WESTERN AND CENTRAL WYOMING BY LATER THIS
AFTERNOON. ANY THUNDERSTORMS WOULD BE LIMITED TO FAR NORTHERN AND
NORTHEASTERN AREAS. THERE COULD BE A COUPLE NEAR THE ABSAROKAS AND
BIG HORNS WHERE SOME WEAK UPSLOPE OR HIGH LEVEL HEAT SOURCE MAY
BRING SOMETHING BUT EVEN HERE THE CHANCE IS LESS THAN 1 OUT OF 5.
THE MAIN STORY TODAY WILL BE THE WARM TEMPERATURES, WITH SOME OF THE
WARMER AREAS, LIKE THE BIGHORN BASIN, HAVING SOME AREAS THAT ECLIPSE
THE 90 DEGREE MARK THIS AFTERNOON. THERE WILL ALSO STILL BE A BIT OF
A BREEZE TODAY, BUT SOMEWHAT LIGHTER THAN YESTERDAY. AREAS IN
NORTHERN JOHNSON COUNTY STILL HAVE AROUND A 1 IN 2 CHANCE OF GUSTS
OVER 35 MPH AT TIMES THIS AFTERNOON THOUGH. ANY CONVECTION SHOULD
END FAIRLY QUICKLY THIS EVENING, WITH DRY WEATHER AFTER MIDNIGHT.
THINGS SHOULD FINALLY START MOVING ON FRIDAY AS THE RIDGE WEAKENS
AND SHIFTS A BIT EAST AND THE LOW BEGINS TO MOVE. FLOW WILL TURN
MORE TO THE SOUTHEAST THROUGH THE DAY AND INCREASE MOISTURE INTO THE
AREA. IT WILL TAKE A WHILE FOR THE ATMOSPHERE TO MOISTEN THOUGH. AS
A RESULT, MOST OF THE DAY SHOULD BE WARM AND DRY WITH ANY CONVECTION
HOLDING OFF UNTIL MID TO LATE AFTERNOON. TEMPERATURES SHOULD RUN
FAIRLY SIMILAR TO TODAY'S HIGHS.
IT IS LOOKING MORE AND MORE LIKELY THAT AT LEAST PORTIONS OF THE
AREA WILL SEE A DECENT AMOUNT OF PRECIPITATION OVER THE WEEKEND.
WHERE IT FALLS DEPENDS UPON WHERE THE LOW EVENTUALLY TRACKS AND BOTH
THE ENSEMBLES AND DETERMINISTIC MODELS CONTINUE TO HAVE DIFFERENT
SOLUTIONS. A FURTHER WEST TRACK, LIKE SOME ENSEMBLE MEMBERS AS WELL
AS THE GFS HAVE, WOULD KEEP THE HEAVIER PRECIPITATION OVER WESTERN
WYOMING. AREAS FURTHER EAST WOULD HAVE A DOWNSLOPING FLOW AND
THEREFORE LESS PRECIPITATION. IF THE LOW IS FURTHER EAST, DECENT
PRECIPITATION WOULD BE SPREAD MORE THROUGHOUT THE AREA. THE WEATHER
PREDICTION CENTER DOES HAVE NORTHERN PORTIONS OF THE AREA IN A
MARGINAL RISK OF EXCESSIVE RAINFALL AS WELL FOR BOTH SATURDAY AND
POSSIBLY SUNDAY AS THE LOW MAY SLOW DOWN AND LINGER CLOSE TO THE
AREA, BUT AGAIN THERE ARE SOLUTIONS ON BOTH SIDES OF THIS EQUATION.
AS FOR PRECIPITATION AMOUNTS, WE WILL TURN TO THE REALM OF THE
ENSEMBLES TO TRY TO ANSWER THIS QUESTION. THE NATIONAL BLEND OF
MODELS GIVES A GREATER THAN 1 IN 2 CHANCE OF A QUARTER OF AN INCH OF
QPF THROUGH MONDAY MORNING ROUGHLY NORTH AND WEST OF A ROCK SPRINGS
TO RIVERTON AND BUFFALO LINE. MUCH NORTHWESTERN WYOMING, INCLUDING
YELLOWSTONE PARK, THE ABSAROKAS AND TETONS HAVE A GREATER THAN 1 IN
2 CHANCE OF AN INCH O QPF OR MORE. STILL SOME UNCERTAINTY FOR EXACT
PLACEMENT, BUT THE CHANCE IS DEFINITELY THERE.
AND THEN WE HAVE TO TAKE A LOOK AT THE POSSIBILITY OF THE "S" WORD,
SNOW. YES, THERE COULD BE SOME SNOW WITH THIS SYSTEM. IT WILL NOT
OCCUR IN THE VALLEYS. HOWEVER, WE ARE GETTING INTO THE TIME OF YEAR
WHEN MOUNTAIN RECREATION INCREASES SUBSTANTIALLY WE HAVE TO LOOK AT
IT. THE GFS GIVES 700 MILLIBAR TEMPERATURES FALLING AS LOW AS MINUS
1, WHICH WOULD PUT SNOW LEVELS AROUND 8000 FEET. THIS MAY BE A BIT
LOW, IT LIKELY CLOSER TO 8500 OR 9000 FEET. HOWEVER, THERE COULD BE
SOME ACCUMULATION. THE NATIONAL BLEND OF MODELS GIVES A GREATER THAN
1 IN 2 CHANCE OF 3 INCHES OF SNOW ABOVE 10000 FEET THROUGH MONDAY
MORNING. SOME OF HIGHEST PEAKS IN THE WIND RIVER RANGE AND TETONS
COULD SEE 6 INCHES OR MORE OF SNOW FROM THIS. IT DOESN'T LOOK TO
IMPACT TRAVEL TO SUBSTANTIALLY SINCE ROADS ARE VERY WARM RIGHT NOW.
HOWEVER, IF YOU ARE TRAVELING OVER MOUNTAIN PASSES, DON'T BE
SURPRISED IF YOU SEE SOME SNOW THIS WEEKEND, ESPECIALLY OVER THE
HIGHER ONES LIKE TOGWOTEE PASS WHICH IS CLOSE TO 10000 FEET IN
ELEVATION.
FOLLOWING THIS, DRIER WEATHER LOOKS TO RETURN TO THE AREA AND FLOW
BECOMES MORE ZONAL WITH FLAT RIDGING BRING DRIER WEATHER AND
TEMPERATURES RETURNING TO MUCH OF THE AREA FOR THE START OF NEXT
WEEK.
AVIATION /18Z TAFS THROUGH 18Z FRIDAY/
ISSUED AT 1030 AM MDT THU MAY 28 2026
VFR CONDITIONS EXPECTED THROUGHOUT THE ENTIRETY OF THE PERIOD AT
ALL TAF SITES. INCREASING WINDS SHORTLY AFTER THE START OF THE
PERIOD THROUGH THE AFTERNOON HOURS DURING PEAK HEATING AND
MIXING TO THE SURFACE. ISOLATED STORM CHANCES NEAR CPR/COD ONCE
AGAIN WITH PROB30 GROUPS BETWEEN 20-23Z BUT CONFIDENCE LOW
(<10%) ON STATION. WINDS DIMINISH AFTER AROUND 02Z TOWARDS
SUNSET WITH RADIATIONAL COOLING EXPECTED TO PICK UP ONCE AGAIN
BY THE END OF THE PERIOD TOWARDS 17-18Z. STORM ACTIVITY ONLY
EXPECTED NEAR CPR FOR FRIDAY AFTERNOON INTO THE NEXT TAF CYCLE.
PLEASE SEE THE AVIATION WEATHER CENTER AND/OR CWSU ZDV AND ZLC FOR
THE LATEST INFORMATION ON ICING AND TURBULENCE FORECASTS.
RIW WATCHES/WARNINGS/ADVISORIES
NONE.
UPDATE...MCDONALD
DISCUSSION...HATTINGS
AVIATION...LOWE
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