223
FXUS65 KMSO 150641
AFDMSO
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MISSOULA MT
1241 AM MDT MON SEP 15 2025
DISCUSSION
KEY MESSAGES:
- COOL AND SHOWERY TODAY
- WARMING AND DRYING BEGINS TUESDAY LASTING THROUGH FRIDAY. FROST
POTENTIAL DIVIDE AND OTHER COMMON VALLEY COLD SPOTS.
- SHOWER/THUNDERSTORM CHANCES RETURN NEXT WEEKEND
AN UPPER LOW WILL MEANDER ACROSS THE NORTHERN ROCKIES TODAY, BRINGING
WIDESPREAD SHOWERS AND NOTICEABLY COOLER CONDITIONS, WITH DAYTIME HIGHS
RUNNING 5-10F BELOW NORMAL. MODEL GUIDANCE SUGGESTS A POSSIBLE
DEFORMATION ZONE ALONG THE CANADIAN BORDER IN NORTHWEST MONTANA,
SUPPORTING PERIODS OF MORE PERSISTENT, MODERATE RAINFALL. FOR MUCH
OF THE REGION, PRECIPITATION WILL TAPER OFF BY LATE AFTERNOON,
THOUGH SCATTERED SHOWERS ARE LIKELY TO LINGER ALONG THE DIVIDE
INTO EARLY TUESDAY. PATCHY VALLEY FOG IS POSSIBLE THIS MORNING IN
AREAS WITH PARTIAL CLEARING AND MORE WIDESPREAD FOG DEVELOPMENT
MAY OCCUR TUESDAY MORNING WHERE OVERNIGHT CLEARING OCCURS,
PARTICULARY THE US 93 CORRIDOR WESTWARD.
CONFIDENCE IS HIGH (NEARLY ALL ENSEMBLE CLUSTERS IN AGREEMENT) THAT
UPPER-LEVEL RIDGING WILL STRENGTHEN OVER THE NORTHERN ROCKIES FROM LATE
TUESDAY THROUGH FRIDAY. THIS PATTERN WILL BRING MOSTLY DRY WEATHER AND A
WARMING TREND, WITH DAYTIME HIGHS RUNNING 5-10F ABOVE NORMAL.
GARDENERS BEWARE, THIS IS A SNEAKY TIME OF YEAR AS LONGER NIGHTS
UNDER CLEAR SKIES OFTEN CAUSE OVERNIGHT LOWS TO BE SEVERAL
DEGREES COOLER THAN GUIDANCE MAY SUGGEST. WATCH FOR FROST
POTENTIAL IN THE HIGHER VALLEYS ALONG THE DIVIDE, ALONG WITH
COMMON COLD SPOTS IN THE BITTEROOT, MISSOULA, AND FLATHEAD
VALLEYS.
BY THE WEEKEND, THE RIDGE BEGINS TO WEAKEN AS WEST TO SOUTHWEST FLOW TAKES
OVER. THIS WILL LEAD TO SLIGHTLY COOLER DAYTIME TEMPERATURES, THE RETURN OF
SHOWER AND THUNDERSTORM CHANCES, AND STRONGER DAILY BREEZES.
AVIATION
AN UPPER LOW WILL MEANDER ACROSS THE NORTHERN ROCKIES TODAY,
PRODUCING WIDESPREAD SHOWERS, PERIODIC REDUCTIONS IN CEILINGS, AND FREQUENT
MOUNTAIN OBSCURATIONS. MODEL GUIDANCE INDICATES A POSSIBLE DEFORMATION ZONE
ALONG THE CANADIAN BORDER IN NORTHWEST MONTANA, WHERE MODERATE RAINFALL MAY
PERSIST THROUGH THE DAY. FOR MOST AREAS, PRECIPITATION WILL TAPER LATER
THIS AFTERNOON, THOUGH SHOWERS ARE EXPECTED TO LINGER ALONG THE DIVIDE INTO
EARLY TUESDAY.
WINDS REMAIN LIGHT TODAY. PATCHY VALLEY FOG IS POSSIBLE THIS MORNING IN
AREAS THAT HAVE PARTIAL CLEARING, AND RENEWED FOG DEVELOPMENT IS LIKELY
TUESDAY MORNING, ESPECIALLY THE US-93 CORRIDOR WESTWARD WHERE
OVERNIGHT CLEARING IS ANTICIPATED.
MSO WATCHES/WARNINGS/ADVISORIES
MT...NONE.
ID...NONE.
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page