187
FXUS65 KRIW 051729
AFDRIW
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
1129 AM MDT SUN JUL 5 2026
KEY MESSAGES
- A HOT DAY TODAY WITH ISOLATED AFTERNOON AND EVENING VIRGA
SHOWERS AND DRY THUNDERSTORMS OCCURRING ALONG AND NORTH OF A
AFTON-TO-WORLAND LINE (A 1 IN 5 CHANCE). ANY SHOWER OR STORM
COULD HAVE STRONG WIND GUSTS UP TO 60 MPH.
- AN INCREASED CHANCE OF SHOWERS AND THUNDERSTORMS MONDAY
THROUGH WEDNESDAY, WITH THE MOST NUMEROUS STORMS EXPECTED ON
TUESDAY. LOCALLY HEAVY RAIN WILL BECOME POSSIBLE WITH THE
STRONGER STORMS MONDAY AND TUESDAY.
- THE HOTTEST TEMPERATURES OF THE YEAR ARE LIKELY FRIDAY THROUGH
SUNDAY WITH RECORD HIGH TEMPERATURES POSSIBLE.
UPDATE
ISSUED AT 1120 AM MDT SUN JUL 5 2026
NOT MUCH CHANGE IN THE FORECAST FOR THIS AFTERNOON. CU CLOUDS
ARE BEGINNING TO FORM OFF THE EAST SLOPES OF THE ABSAROKA AND
WIND RIVER MOUNTAINS AND THE SALT RIVER/WYOMING RANGES AS OF
11AM. BUFFALO, THERMOPOLIS AND CODY ARE ALREADY 90F. VIRGA
SHOWERS/DRY THUNDERSTORMS ARE EXPECTED TO BE DEVELOPING OVER THE
WESTERN MOUNTAINS BY 2PM, MOVING TO THE NORTHEAST THROUGH THE
REST OF THE AFTERNOON INTO THE EVENING. MOST OF THIS ACTIVITY
WILL OCCUR ALONG AND NORTH OF A AFTON-TO-WORLAND LINE, ENDING
AROUND MIDNIGHT. WIND GUSTS UP TO 60 MPH WILL BE THE MAIN
THREAT, DUE TO THE LARGE DEWPOINT DEPRESSIONS/INVERTED-V
SOUNDING PROFILE IN PLACE TODAY. NEEDLESS TO SAY, FIRE WEATHER
CONDITIONS WILL BE ELEVATED THIS AFTERNOON DUE TO THE HOT
TEMPERATURES AND CRITICALLY LOW RH VALUES. THE GOOD NEWS WILL BE
WINDS WILL BE RELATIVELY LIGHT, GENERALLY STAYING 20 MPH OR
LESS, APART FROM ANY STRONG OUTFLOW WINDS THAT COULD OCCUR.
DISCUSSION
ISSUED AT 136 AM MDT SUN JUL 5 2026
WE HAVE NOW REACHED THE END OF THE HOLIDAY WEEKEND. ALL IN ALL, THE
FOURTH OF JULY WAS PRETTY NICE, WITH WARM TEMPERATURES, NO
CONVECTION AND LOTS OF SUNSHINE. ALL THAT EXCEPT FOR A NEW FIRE
START SOUTHEAST OF LANDER. BUT, WE DON'T WANT TO TALK ABOUT THE
PAST, LET'S TALK ABOUT THE FUTURE, THIS IS A FORECAST AFTER ALL.
THERE WILL BE TWO CHANGES. THE FIRST WILL BE WARMER TEMPERATURES
TODAY AS FLOW TURNS SOUTHWEST AHEAD OF A WEAK COLD FRONT.
TEMPERATURES SHOULD AVERAGE AROUND 5 DEGREES WARMER THAN
YESTERDAY, MAKING THIS THE HOTTEST DAY FOR QUITE A WHILE,
POSSIBLY THE HOTTEST SO FAR THIS YEAR. THIS IS LOOKING LIKE THE
DAY WHEN WE WILL SEE THE FIRST 100 DEGREE HIGH TEMPERATURES OF
THE YEAR, WITH MUCH OF THE EASTERN AND SOUTHERN BIGHORN BASIN
HAVING AROUND A 1 IN 2 CHANCE OF SEEING HIGHS AT OR OVER THE
CENTURY MARK. JUST ABOUT ALL LOCATIONS EAST OF THE DIVIDE IN
THE LOWER ELEVATIONS WILL SEE HIGHS IN THE 90S, WITH SOME 80S TO
LOW 90S WEST OF THE DIVIDE. THE SECOND CHANGE IS THE CHANCE FOR
CONVECTION RETURNS. THE ATMOSPHERE REMAINS RATHER DRY
(PRECIPITABLE WATER VALUES ARE BELOW NORMAL). HOWEVER, THERE IS
ENOUGH MID LEVEL MOISTURE FOR SOME ISOLATED SHOWERS AND
THUNDERSTORMS ACROSS NORTHWESTERN WYOMING, LARGELY WEST AND
NORTH OF A FRANNIE TO ALPINE LINE. THE ONLY HAZARD WOULD BE
STRONG WIND GUSTS. THERE ARE VERY STEEP LOW LEVEL LAPSE RATES
(GREATER THAN 9C/KM) ALONG WITH VERY LARGE DEWPOINT DEPRESSIONS
(UP TO 60 DEGREES). ALL THIS ADDS UP TO THE THREAT OF
MICROBURSTS, EVEN FROM SMALL SHOWERS (THE INFAMOUS "LITTLE GREEN
BLOBS)." COVERAGE WILL BE SMALL, GENERALLY LESS THAN 1 OUT OF 5
IN THE IMPACTED AREA. MOST OF THESE SHOWERS SHOULD END SHORTLY
AFTER SUNSET WITH DRY CONDITIONS THROUGH MONDAY MORNING.
ELSEWHERE, ELEVATED FIRE WEATHER IS LIKELY WITH HUMIDITY FALLING
INTO THE SINGLE DIGITS AT TIMES. LARGELY LIGHT WIND SHOULD KEEP
CONDITIONS FROM BECOMING CRITICAL.
A COLD FRONT (OR A REASONABLE FACSIMILE OF ONE) THEN SLIPS INTO
NORTHERN WYOMING, GETTING CLOSE TO THE CONTINENTAL DIVIDE BY
MONDAY MORNING. THIS SHOULD KNOCK HIGH TEMPERATURES DOWN AROUND
5 TO 10 DEGREES COMPARED TO TODAY. THE OTHER DIFFERENCE WILL BE
AN INCREASE IN MOISTURE AS LOW PRESSURE PASSES TO THE SOUTHEAST
OF WYOMING AND TURNS LOW LEVEL FLOW TO THE SOUTH AND SOUTHEAST.
PRECIPITABLE WATER VALUES RISE TO AROUND 125 TO 150 PERCENT OF
NORMAL BY 00Z TUESDAY. THIS MEANS AN INCREASE IN CONVECTION
ACROSS THE AREA, AND MAYBE SOME NEEDED RAIN. MOST GUIDANCE
FAVORS NORTHERN WYOMING, WHERE GREATEST INSTABILITY WILL BE
FOUND (UP TO AROUND 500 J/KG OF CAPE). MOST SOUNDINGS SHOW A
DECENT CAP INITIALLY, SO THIS IS FAVORED TO BE A LATER SHOW,
MAINLY IN THE EVENING WITH SOME CONVECTION LINGERING INTO THE
OVERNIGHT HOURS. GUIDANCE IS FAIRLY CONSISTENT IN HAVING THE
HIGHEST CHANCE (UP TO A 1 OUT OF 2 CHANCE) ACROSS NORTHERN
WYOMING, WITH DECREASING POPS FURTHER SOUTH, WITH LITTLE CHANCE
IN SOUTHEASTERN SWEETWATER COUNTY. MOST STORMS SHOULD NOT REACH
SEVERE LIMITS, BUT THERE COULD BE A FEW.
STORM COVERAGE SHOULD PEAK ON TUESDAY. A MORE DEFINED SHORTWAVE
WILL BE MOVING THROUGH THE AREA. PRECIPITABLE WATER VALUES ALSO
REACH A MAXIMUM ON THIS DAY, WITH MANY LOCATIONS SEEING GREATER THAN
150 PERCENT OF NORMAL AND SOME LOCATIONS REACHING VALUES OVER AN
INCH. THE ATMOSPHERE IS ALSO THE MOST UNSTABLE ON THIS DAY, WITH
NEGATIVE LIFTED INDICES ACROSS THE ENTIRE AREA. AS FOR STRONGER
STORMS, AGAIN THE MOST FAVORED LOCATION WOULD BE ACROSS THE NORTH
WHERE THE GREATEST CAPE (>1000 J/KG) AND LIFTED INDICES (DOWN
TO MINUS 4) WILL BE FOUND. THERE WILL BE SOME MOVEMENT WITH THE
STORMS AND WITH THE RECENT DRY WEATHER THERE IS ROOM IN THE
SOIL, BUT LOCALLY HEAVY RAIN CANNOT BE RULED OUT DUE TO THE
MOIST ATMOSPHERE. MOST OF THESE STORMS SHOULD END AFTER SUNSET.
MORE CLOUD COVER SHOULD ALSO KEEP TEMPERATURES COOLER ON THIS
DAY, WITH THE CURRENT FORECASTED HIGHS BEING A BIT TOO WARM AND
MAY TREND A BIT COOLER.
STARTING ON WEDNESDAY, WE WILL HAVE WHAT IS CALLED AN INVERSE
RELATIONSHIP. A VERY STRONG RIDGE WILL BEGIN BUILDING ACROSS THE
DESERT SOUTHWEST AND WILL BE EXPANDING NORTHWARD LATE NEXT WEEK
AND ESPECIALLY INTO NEXT WEEKEND. THE INVERSE RELATIONSHIP WILL
BE TEMPERATURES GOING UP, AND CHANCES OF CONVECTION GOING DOWN.
ON WEDNESDAY, THERE WILL STILL BE ENOUGH LINGERING MOISTURE FOR
A DECENT COVERAGE OF STORMS, BUT MORE SCATTERED. DRIER AIR
REALLY SURGES INTO THE AREA STARTING THURSDAY, ANY STORMS WOULD
BE RESTRICTED TO EASTERN PORTIONS OF THE AREA ON THIS DAY.
TEMPERATURES REALLY BEGIN CLIMBING ON FRIDAY AND ESPECIALLY INTO
THE WEEKEND. MANY RUNS OF THE ENSEMBLES CENTER THE RIDGE ON OR
VERY CLOSE TO WYOMING, WITH 500 MILLIBAR HEIGHTS AS HIGH AS 6000
METERS. THIS IS THE CLASSIC DEFINITION OF A DEATH RIDGE,
BRINGING VERY HOT TEMPERATURES AND LITTLE TO NO CHANCE OF RAIN.
ENSEMBLE FORECASTS START GIVING AT LEAST A 2 OUT OF 5 CHANCE OF
HIGHS OVER 100 ONCE AGAIN IN THE TYPICALLY WARM LOCATIONS BY
FRIDAY. BUT THE WEEKEND IS WHERE THE HEAT MAY REALLY HIT. ON
BOTH SATURDAY AND SUNDAY, THE NBM ENSEMBLE GIVES A GREATER THAN
3 OUT OF 5 CHANCE OF TRIPLE DIGIT HIGHS BOTH DAYS FOR AREAS EAT
OF THE DIVIDE BELOW 5500 FEET. SOME OF THE TYPICALLY WARMER
SPOTS, LIKE GREYBULL AND WORLAND HAVE A 2 OUT OF 5 CHANCE OF
HIGHS OVER 105. A WORD OF CAUTION, THIS IS STILL A WEEK OUT AND
THINGS CAN CHANGE. HOWEVER, WE DO HAVE THE CHANCE OF ONE OF THE
MORE NOTABLE HEATWAVES WE HAVE SEEN IN A WHILE.
AVIATION /18Z TAFS THROUGH 18Z MONDAY/
ISSUED AT 1105 AM MDT SUN JUL 5 2026
VFR CONDITIONS PREVAIL THROUGH THE PERIOD. CLOUDS INCREASE FROM THE
WEST THROUGH THIS AFTERNOON AND EVENING. A FEW SHOWERS AND
THUNDERSTORMS ARE POSSIBLE, MAINLY ACROSS THE WESTERN MOUNTAINS,
WITH PROB30 GROUPS AT KCOD AND KJAC. A FEW SHOWERS COULD BE AS SOUTH
AS KBPI AND KPNA THIS AFTERNOON. A WEAK COLD FRONT MOVES IN FROM THE
NORTH AFTER 00Z, BRING A NORTHERLY WIND SHIFT TO SITES EAST OF
THE DIVIDE. A FEW HOURS OF GUSTY WINDS ARE POSSIBLE WITH THE
FRONTAL PASSAGE.
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...LAVOIE
DISCUSSION...HATTINGS
AVIATION...WITTMANN
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