475
FXUS65 KRIW 280801
AFDRIW
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
201 AM MDT THU AUG 28 2025
KEY MESSAGES
- ANOTHER COOLER DAY WITH SHOWER AND ISOLATED THUNDERSTORM
CHANCES (50-90%). THE GREATEST COVERAGE OF SHOWERS AND
THUNDERSTORM IS FORECAST ACROSS NORTHWESTERN WYOMING AND EAST
OF THE DIVIDE.
- MORE SCATTERED SHOWER AND THUNDERSTORM CHANCES (30-70%) FRIDAY
AND SATURDAY EAST OF THE DIVIDE.
- TEMPERATURES INCREASE TO NEAR TO SLIGHTLY ABOVE NORMAL SUNDAY
INTO EARLY NEXT WEEK WITH LIMITED PRECIPITATION CHANCES.
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 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.
DISCUSSION...GERHARDT
AVIATION...DZIEWALTOWSKI
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