227
FXUS65 KMSO 090658
AFDMSO
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MISSOULA MT
1258 AM MDT FRI MAY 9 2025
DISCUSSION
KEY MESSAGES:
- TODAY INTO SATURDAY WARMEST TEMPERATURES SO FAR THIS YEAR,
CAUSING SIGNIFICANT INCREASE IN RIVER/STREAM FLOWS
- SCATTERED THUNDERSTORMS SATURDAY AND SUNDAY AFTERNOONS,
POTENTIALLY A FEW STRONG TO SEVERE STORMS
- SNOW POTENTIALLY TO 5500 FEET ACROSS SOUTHWEST MONTANA TUESDAY
INTO WEDNESDAY.
RIDGING BUILDS BACK IN TODAY AND SATURDAY WITH WARM AND MOSTLY DRY
CONDITIONS ACROSS THE NORTHERN ROCKIES. BY SATURDAY AFTERNOON,
MID LEVEL MOISTURE, INSTABILITY, AND SHEAR COMBINE FOR SCATTERED
HIGH BASED SHOWERS AND THUNDERSTORMS, MAINLY FOR SOUTHWEST MONTANA
AND LEMHI COUNTY BUT MAY STRETCH AS FAR NORTH AS THE I-90
CORRIDOR. WATCH FOR STRONG WIND GUST POTENTIAL OVER 50 MPH FROM
ANY CONVECTION AS BACKGROUND GRADIENT DRIVEN WINDS WILL ALREADY BE
GUSTING AT 25-35 MPH REGARDLESS OF CONVECTION. GIVEN THE SHEAR
PROFILE, HAIL IS ALSO A CONCERN.
THIS WARM PERIOD WILL ACCELERATE SNOWPACK MELT OFF, WITH STREAM
AND RIVER FLOWS EXPECTED TO RISE SIGNIFICANTLY IN RESPONSE.
CURRENT RIVER/ STREAM FLOW MODELING DOES HAVE A COUPLE LOCATIONS
RISING CLOSE TO ACTION STAGE BY MAY 12-13 BUT NO FLOODING IS
EXPECTED.
SUNDAY, THE RIDGE BREAKDOWN IS EXPECTED WITH A SIGNAL OF
INCREASED INSTABILITY AND MOISTURE. SHOWERS AND THUNDERSTORMS WILL
BE PRESENT AHEAD OF AND ALONG A PACIFIC COLD FRONT. A STRONG TO
SEVERE STORM OR TWO WITH HAIL AND DAMAGING WINDS CAN NOT BE RULED
OUT IN THIS ENVIRONMENT. ALSO AHEAD OF THE FRONT, WATCH FOR GUSTY
WINDS OF 30-40 MPH ACROSS LEMHI COUNTY AND SOUTHWEST MONTANA ON
SUNDAY AFTERNOON. THERE CONTINUES TO BE AN INDICATION THAT THE
FRONT MAY BE A LITTLE SLOWER TO MOVE SOUTH ACROSS LEMHI COUNTY AND
SOUTHWEST MONTANA INTO MONDAY. THE MAIN TROUGH ACROSS WASHINGTON
TO NORTHERN CALIFORNIA BEGINS TO EXHIBIT MORE OF A NEGATIVE TILT.
THIS CAUSES THE FLOW ALOFT TO BECOME MORE SOUTHEASTERLY, THEREBY
OPPOSING THE INCOMING FRONTAL SYSTEM AND SLOWING IT DOWN. THE
EFFECTS OF THIS COULD BE MORE RAINFALL POTENTIAL ACROSS IDAHO IN
THE POST-FRONTAL REGIME (ANAFRONT), BUT WARMER ACROSS SOUTHWEST
MONTANA. IT COULD ALSO BRING ANOTHER ROUND OF STORMS ALONG THE
FRONT.
CLUSTERS ARE CONTINUING TO SHOW A YELLOWSTONE LOW FORMING TUESDAY
INTO WEDNESDAY. DEJA VU? THIS PATTERN LOOKS VERY SIMILAR TO WHAT
OCCURRED JUST A FEW DAYS AGO. SNOW LEVELS COULD FALL TO 5500 FEET
AND THERE COULD BE WINTRY IMPACTS AT HIGH LEVEL LOCATIONS ACROSS
SOUTHWEST MONTANA. WHILE IT APPEARS THAT A MAJORITY OF THE
CLUSTERS SUGGEST THE HEAVIER SNOWFALL AMOUNTS WILL GENERALLY BE
EAST OF SOUTHWEST MONTANA, THERE IS ONE CLUSTER THAT SHOWS THAT 44
PERCENT OF THE ECMWF ENSEMBLE MEMBERS, 20 PERCENT OF THE GFS
ENSEMBLE AND 10 PERCENT OF CANADIAN ENSEMBLE MEMBERS DEPICT A
SNOWIER SOLUTION. IN ADDITION TO THE PASS LEVEL SNOW, THIS
CLUSTER SOLUTION WOULD ALSO ALLOW FOR WIDESPREAD RAINFALL TO
LOWER ELEVATION AREAS ALONG AND SOUTH OF THE I-90 CORRIDOR. STAY
TUNED AS THE DETAILS COME TOGETHER!
AVIATION: RIDGING BUILDS BACK IN TODAY WITH VFR CONDITIONS ACROSS
THE NORTHERN ROCKIES. HIGH AND MID LEVEL CLOUD COVER WILL PASS
THROUGH BUT NO MOUNTAIN OBSCURATIONS ARE ANTICIPATED. BREEZY
AFTERNOON WINDS WITH GUSTS OF 15-25 KTS ARE ANTICIPATED AT MOST
AIRFIELDS AS A RESULT OF PEAK DIURNAL INSTABILITY. WINDS DIMINISH
QUICKLY BY SUNSET WITH THE LOSS OF DAYTIME HEATING. CHANGES ARRIVE
ON SATURDAY WITH SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS,
MAINLY ACROSS SOUTHWEST MONTANA AND LEMHI COUNTY. WIND GUSTS OF
20-30 KTS WILL BE COMMON ON SATURDAY AFTERNOON BUT THUNDERSTORM
OUTFLOW WILL ALLOW FOR GUST POTENTIAL OVER 45 KTS.
MSO WATCHES/WARNINGS/ADVISORIES
MT...NONE.
ID...NONE.
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