912
FXUS65 KRIW 290349
AFDRIW
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
949 PM MDT THU AUG 28 2025
KEY MESSAGES
- AN EARLY AUTUMN LIKE DAY ACROSS MUCH OF THE COWBOY STATE TODAY
WITH ISOLATED TO SCATTERED SHOWERS AND THUNDERSTORMS POSSIBLE
THIS AFTERNOON ACROSS NORTHERN AND WESTERN WY.
- SHOWER AND THUNDERSTORM CHANCES REMAIN ISOLATED FOR FRIDAY AND SATURDAY
WITH THE BEST CHANCES OVER NORTHERN WY.
- DRIER AND WARMER CONDITIONS LOOK TO RETURN TO THE REGION FOR
THE END OF THE WEEKEND INTO THE FIRST HALF OF NEXT WEEK.
UPDATE
ISSUED AT 1233 PM MDT THU AUG 28 2025
SOME MUCH NEED PRECIPITATION FELL ACROSS THE COWBOY STATE YESTERDAY
WITH MANY LOCATIONS SEEING ANYWHERE FROM 0.25 TO 1.00 INCHES OF
LIQUID. THE ONLY EXCEPTION TO THIS WAS OVER NORTHERN WY IN LOCATIONS
SUCH AS THE BIGHORN BASIN AND JOHNSON COUNTY WHERE PRECIPITATION
STRUGGLED TO REACH. THESE LOCATIONS SAW ANYWHERE FROM NO
PRECIPITATION TO A FEW HUNDREDTHS OF LIQUID. FORTUNATELY,
BETTER CHANCES FOR RAINFALL SHOULD ARRIVE THIS AFTERNOON AND
EVENING.
THE FORECAST HAS SEEN A FEW CHANGES FROM OVERNIGHT WITH SHOWER AND
THUNDERSTORM COVERAGE CONTINUING TO DECREASE. CURRENTLY THE BEST
CHANCES (30-50%) LOOK TO BE ACROSS WESTERN AND NORTHERN WY. CENTRAL
AND SOUTHERN WY HAS SEEN CHANCES DECREASE WITH PRECIPITATION LOOKING
TO BE VERY ISOLATED IN NATURE THIS AFTERNOON AND EVENING.
TEMPERATURES ARE FORECAST TO BE ON THE COOLER SIDE FOR MUCH OF THE
STATE WITH HIGHS IN THE MID TO UPPER 60S WEST OF THE DIVIDE AND MID
TO UPPER 70S EAST OF THE DIVIDE. WARMER TEMPERATURES IN THE LOW TO
MID 80S ARE POSSIBLE IN PARTS OF THE BIGHORN BASIN WHERE MORE BREAKS
IN THE CLOUD COVER IS EXPECTED. PRECIPITATION CHANCES LOOK TO
DECREASE FOR FRIDAY AND SATURDAY WITH LESSER CHANCES OVER MUCH OF
THE AREA. THE BEST CHANCES PREVAIL OVER NORTHERN WY BUT STILL LOOK
ISOLATED IN NATURE (10-30%). TEMPERATURES REMAIN AROUND TO SLIGHTLY
BELOW SEASONABLE VALUES WITH A SLIGHT WARM UP EXPECTED BY SUNDAY
INTO THE FIRST HALF OF NEXT WEEK. THE LONG RANGE FORECAST CONTINUES
TO SHOW WARMER AND MOSTLY DRIER CONDITIONS THROUGH MUCH OF THE
UPCOMING WEEK.
DISCUSSION
ISSUED AT 200 AM MDT THU AUG 28 2025
08Z WATER VAPOR IMAGERY SHOWS A NEGATIVELY TILTED UPPER-LEVEL RIDGE
OVER THE INTERMOUNTAIN WEST AND AN UPPER-LEVEL LOW CENTER OVER THE
PACIFIC NORTHWEST EXTENDING INTO IDAHO AND MONTANA. AS TODAY
PROGRESSES, A BUILDING UPPER RIDGE OVER THE GREAT BASIN WILL PUSH
THE LOW NORTH AND INTERMOUNTAIN WEST RIDGE EAST. WITH ENHANCED
VORTICITY ALOFT AND DEEP MOISTURE, ANOTHER DAY OF RAINY WEATHER IS
FORECAST. HOWEVER, DIFFERING FROM WEDNESDAY, THE GREATEST COVERAGE
OF SHOWERS AND ISOLATED THUNDERSTORMS WILL BE EAST OF THE DIVIDE,
WHERE SUPPORT ALOFT IS MAXIMIZED AND MEAN PWATS GENERALLY RANGE FROM
0.75 INCH TO 1.2 INCH. SHOWERS AND ISOLATED THUNDERSTORMS WILL ALSO
BE COMMON ACROSS WESTERN WYOMING, INCLUDING YELLOWSTONE NATIONAL
PARK, GIVEN FAVORABLE UPSLOPING FLOW. ADDITIONALLY, AN UPPER-LEVEL
WIND MAXIMUM ROUNDING A FOUR CORNERS UPPER-HIGH WILL BE PRESENT OVER
SOUTHERN WYOMING THIS AFTERNOON ALONG WITH A TIGHTENING PRESSURE
GRADIENT. THIS TRANSLATES TO FREQUENT 20 TO 25 MPH GUSTS ACROSS
SOUTHERN WYOMING.
ON FRIDAY, THE UPPER-LEVEL GREAT BASIN RIDGE CONTINUES TO BUILD
NORTHWARD AND THE UPPER-LOW IS FORECAST TO ROUGHLY BE CENTERED OVER
THE MONTANA/CANADA BORDER. THIS LEAVES WYOMING IN DEEP NORTHWEST
FLOW. THE LOW'S SURFACE REFLECTION IS EXPECTED TO TREK SOUTHEAST
FROM MONTANA INTO THE SOUTH DAKOTA/NEBRASKA AREA, FOCUSING SHOWER
AND THUNDERSTORM CHANCES EAST OF THE DIVIDE. THE GREATEST RAINFALL
AMOUNTS, GENERALLY AROUND 0.25 INCHES, WILL BE ACROSS THE NORTHERN
BIGHORN MOUNTAINS DUE TO UPSLOPING. BY SATURDAY, A SHORTWAVE WILL
PROVIDE SUPPORT ALOFT FOR SCATTERED SHOWERS AND POTENTIALLY
THUNDERSTORMS EAST OF THE DIVIDE DURING THE AFTERNOON AND EARLY
EVENING HOURS.
THERE IS CONSENSUS AMONG ENSEMBLE GUIDANCE MEMBERS THAT THE UPPER-
LEVEL RIDGE WILL CONTINUE TO BUILD ACROSS THE WESTERN CONUS SUNDAY
AND REMAIN THROUGH MUCH OF NEXT WEEK, KEEPING THE INTERMOUNTAIN WEST
IN NORTHWEST FLOW ALOFT. ASSOCIATED HEIGHT RISES AT THE SURFACE AND
A LACK OF MOISTURE WILL LIMIT PRECIPITATION CHANCES SUNDAY THROUGH AT
LEAST THE MIDDLE OF NEXT WEEK. DESPITE NORTHWEST FLOW ALOFT, A WARM
UP TO NEAR TO SLIGHTLY ABOVE NORMALS LOOKS FAVORABLE DURING THIS
TIMEFRAME.
AVIATION /06Z TAFS THROUGH 06Z SATURDAY/
ISSUED AT 948 PM MDT THU AUG 28 2025
VFR CONDITIONS ARE EXPECTED FOR ALL TAF SITES MOST OF THE NIGHT.
A FEW SHOWERS MAY OCCUR IN VICINITY OF KCOD, BUT CONDITIONS ARE
EXPECTED TO REMAIN VFR. FOG IS AGAIN POSSIBLE AROUND KLND AND
KRIW TONIGHT. WE HAVE ELECTED TO GO WITH VICINITY FOR NOW AS IT
IS NOT A CERTAINTY. THE MOST LIKELY TIME WOULD BE FROM 11Z
THROUGH 16Z FRIDAY.LARGELY VFR CONDITIONS ARE EXPECTED ON
FRIDAY. ISOLATED CONVECTION IS POSSIBLE AGAIN IN THE NORTHERN
TAF SITES (MAINLY IN VICINITY OF KWRL AND KCOD) BUT THE CHANCE
IS MUCH LESS THAN TODAY, MAINLY LESS THAN 1 OUT OF 3 AT ANY SPOT
SO WE HAVE ELEVATED TO GO WITH PROB30 GROUPS FOR NOW RATHER
THAN PREVAILING.
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...DZIEWALTOWSKI
DISCUSSION...GERHARDT
AVIATION...HATTINGS
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