630
FXUS65 KRIW 080117
AFDRIW
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
717 PM MDT MON SEP 7 2026
KEY MESSAGES
- EARLY AUTUMN HAS COME TO WESTERN WYOMING HIGHER-ELEVATION
VALLEYS AND BASINS, WITH NEAR-FREEZING TEMPERATURES FORECAST
AROUND SUNRISE BOTH TUESDAY AND WEDNESDAY MORNING. SENSITIVE
OUTDOOR PLANTS COULD BE AFFECTED BY FREEZE AND FROST.
- BREEZY WINDS AND LOW HUMIDITY WILL LEAD TO CONTINUED FIRE
WEATHER CONCERNS THROUGH THE WORK WEEK. CONFIDENCE IS
INCREASING FOR A WEEKEND WEATHER SYSTEM TO BRING COOLER AND
WETTER CONDITIONS TO THE AREA.
- TEMPERATURES REMAIN NEAR SEASONAL NORMALS THROUGH MID-WEEK,
WITH ABUNDANT SUNSHINE AND MINIMAL CHANCES FOR RAIN, EVEN IN
THE MOUNTAINS.
UPDATE
ISSUED AT 123 PM MDT MON SEP 7 2026
WITH THIS MORNING'S RAIN NOW FINISHED, THE FOCUS RETURNS TO FIRE
WEATHER. AS NOTED BELOW, THE GREATEST CONCERN THIS AFTERNOON IS
ACROSS THE BIGHORN BASIN, THOUGH MOST AREAS EAST OF THE DIVIDE WILL
BE NEAR-CRITICAL GIVEN THE GUSTY WINDS AND LOW HUMIDITY. A VERY
SIMILAR STORY IS EXPECTED TOMORROW THOUGH WIND WILL NOT BE QUITE AS
ROBUST. REGARDLESS, ADDITIONAL RED FLAG WARNINGS MAY BE NEEDED
TUESDAY, POTENTIALLY EXPANDED THROUGH MUCH OF THE UPCOMING WEEK.
DISCUSSION
ISSUED AT 235 AM MDT MON SEP 7 2026
SHOWERS CONTINUE TO SUBSIDE OVER THE NORTHERN HALF OF THE
FORECAST AREA EARLY THIS MORNING, WITH ISOLATED THUNDERSTORMS
OVER FAR WESTERN PORTIONS. THIS PRECIPITATION WILL END ACROSS
THE AREA BY 15Z THIS MORNING AS WINDS BEGIN TO INCREASE. A DRY
SLOT WILL BE IN PLACE OVER THE COWBOY STATE BY THIS TIME, WITH
THE MAIN SFC LOW IN THE VICINITY OF MT/ND AND THE ASSOCIATED
OCCLUDED LOW OVER WESTERN MT. WEST-SOUTHWEST WINDS, WITH GUSTS
OF 25 TO 35 MPH WILL BE IN PLACE FROM KEMMERER TO CASPER BY THIS
TIME. HIGHER WINDS OF 30 TO 45 MPH WILL OCCUR OVER PORTIONS OF
YNP AND THE EAST SLOPES OF THE ABSAROKA, BIGHORN AND WIND RIVER
MOUNTAINS. WINDS WILL CONTINUE TO INCREASE ACROSS THE FORECAST
AREA, WITH GUSTS OF 25 TO 40 MPH OCCURRING FOR MOST AREAS BY
18Z. FIRE WEATHER WILL ONCE AGAIN BE A CONCERN AS A RESULT, WITH
NEAR- CRITICAL RH VALUES RETURNING. THIS WILL BE ESPECIALLY
TRUE EAST OF THE DIVIDE, WHERE CRITICAL RHS WILL BE IN PLACE IN
THE BIGHORN BASIN. A RED FLAG WARNING IS IN EFFECT FOR BIG HORN,
WASHAKIE AND HOT SPRINGS COUNTIES THIS AFTERNOON AS A RESULT. A
COLD FRONT WILL MOVE EASTWARD THROUGH THE AFTERNOON, EXITING
THE CWA INTO SOUTHEAST WY BETWEEN 06Z AND 09Z TUESDAY. WINDS
WILL SUBSIDE THROUGH THE EVENING, BECOMING LIGHT FOR MUCH OF THE
AREA AFTER MIDNIGHT. FREEZING TEMPERATURES WILL BE POSSIBLE IN
THE WESTERN VALLEYS AND PORTIONS OF THE UPPER GREEN RIVER BASIN
TUESDAY MORNING IN THE WAKE OF THE COLD FRONT.
MORE SEASONAL TEMPERATURES AND DRY CONDITIONS WILL REMAIN IN
PLACE TUESDAY, WITH FREEZING TEMPERATURES POSSIBLE AGAIN IN THE
WESTERN VALLEYS AND UPPER GREEN RIVER BASIN TUESDAY
NIGHT/WEDNESDAY MORNING. NEEDLESS TO SAY, SUB-FREEZING
TEMPERATURES WILL BE IN PLACE IN THE HIGHER ELEVATIONS THE NEXT
TWO NIGHTS. FIRE WEATHER WILL BE THE MAIN CONCERN THROUGH THE
REST OF THE WEEK. WEST-SOUTHWEST WINDS, WITH GUSTS OF 25 TO 35
MPH, WILL OCCUR EACH AFTERNOON WITH SLIGHTLY STRONGER GUSTS
POSSIBLE THURSDAY AND FRIDAY. CRITICAL RHS WILL BE WIDESPREAD
EAST OF THE DIVIDE TUESDAY, SPREADING ACROSS SOUTHERN PORTIONS
WEDNESDAY. AN EXTENDED PERIOD OF RED FLAG WARNINGS LOOKS LIKELY.
MODELS CONTINUE TO TREND TOWARD A STRONG COLD FRONT IMPACTING
THE COWBOY STATE NEXT WEEKEND. THE GFS CONTINUES TO BE THE MOST
AGGRESSIVE, DIGGING A CANADIAN LOW SOUTHWARD TO NORTHERN
PORTIONS OF THE GREAT BASIN AND SPREADING WIDESPREAD
PRECIPITATION OVER THE STATE AHEAD OF IT. THE ECMWF IS SLOWER
AND NOT AS PROGRESSIVE, KEEPING THE SYSTEM OVER THE NORTHERN
ROCKIES AND MOVING OVER THE REGION SUNDAY INTO MONDAY NEXT WEEK.
ALTHOUGH THE TIMING REMAINS INFLUX, THIS CONTINUES TO TREND
TOWARD THE FIRST TASTE OF AUTUMN TO THE REGION.
AVIATION /00Z TAFS THROUGH 00Z WEDNESDAY/
ISSUED AT 349 PM MDT MON SEP 7 2026
VFR CONDITIONS THROUGH THE PERIOD. THE STRONGEST WINDS FROM THIS
AFTERNOON DECREASE BETWEEN 00Z AND 04Z. CLOUDS ALSO DECREASE FOR THE
OVERNIGHT HOURS. A MOSTLY CLEAR SKY IS EXPECTED THROUGH TUESDAY,
WITH INCREASING CLOUDS OVER NORTHERN WYOMING. WINDS 20 TO 30 KNOTS
OCCUR AT MOST SITES TUESDAY AFTERNOON.
PLEASE SEE THE AVIATION WEATHER CENTER AND/OR CWSU ZDV AND ZLC FOR
THE LATEST INFORMATION ON ICING AND TURBULENCE FORECASTS.
FIRE WEATHER
ISSUED AT 235 AM MDT MON SEP 7 2026
RAIN SHOWERS WILL END ACROSS THE AREA BY 0900 THIS MORNING, WITH
CONDITIONS REMAINING DRY THROUGH THE REST OF THE DAY. WINDS
WILL INCREASE ACROSS THE AREA DURING THIS TIME WITH GUSTS UP TO
30 MPH ALREADY OCCURRING FROM KEMMERER TO CASPER. HIGHER GUSTS
OF 35 TO 45 MPH ARE EXPECTED IN THE MOUNTAINS AND NORTHWESTERN
PORTIONS BY 0900 AS WELL. WINDS WILL CONTINUE TO INCREASE ACROSS
THE AREA THROUGH THE REST OF THE MORNING, WITH GUSTS OF 30 TO
40 MPH OCCURRING FOR MOST LOCATIONS BY 1200. CRITICAL RHS WILL
BE CONFINED TO ZONES 275/282 THIS AFTERNOON, BUT OTHER AREAS
EAST OF THE DIVIDE WILL HAVE RHS RANGING BETWEEN 16 AND 20%. A
COLD FRONT WILL PUSH INTO NORTHERN PORTIONS OF THE BIGHORN BASIN
BETWEEN 1300 AND 1500, PROGRESSING TO THE SOUTH AND EAST
THROUGH THE AFTERNOON REACHING GREYBULL/BASIN BY 1800. THE FRONT
WILL PASS THROUGH THE REST OF THE BIGHORN BASIN BY 2100 AS WINDS
DECREASE ACROSS THE AREA.
RED FLAG CONDITIONS ARE LIKELY THROUGH THE REST OF THE WEEK,
WITH MULTI-DAY RED FLAG WARNINGS EXPECTED.
RIW WATCHES/WARNINGS/ADVISORIES
NONE.
UPDATE...MYERS
DISCUSSION...LAVOIE
AVIATION...WITTMANN
FIRE WEATHER...LAVOIE
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