223 FXUS65 KMSO 150641 AFDMSOArea 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.
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.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.
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.MSO WATCHES/WARNINGS/ADVISORIES... MT...None. ID...None. &&
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NWS MSO Office Area Forecast Discussion