032 FXUS65 KMSO 130721 AFDMSOArea Forecast Discussion National Weather Service Missoula MT 121 AM MDT Sat Sep 13 2025
.DISCUSSION...
KEY MESSAGES:
- Patchy morning valley fog today, followed by scattered afternoon showers and thunderstorms under a northwesterly flow
- Significant uncertainty persists for a weather system early next week, with model guidance showing a wide range of possibilities from very little rain to widespread, beneficial precipitation.
Early morning showers/thunderstorms continue in northwest Montana but they will gradually diminish as they push southward. Otherwise, patchy valley fog could develop this morning in locations that have seen recent rainfall. High pressure will attempt to build into the region, but a persistent northwesterly flow aloft will keep the pattern somewhat unsettled today. During the afternoon, daytime heating will combine with the cool, unstable northwesterly flow to trigger scattered showers and isolated thunderstorms, mostly anchored to the terrain.
By Sunday, the flow becomes more westerly and stable, which should result in a drier and sunnier first half of the day for most. Clouds will begin to increase Sunday afternoon as the next weather system approaches from the Pacific. This system is forecast to move into the Northern Rockies on Monday, bringing a return to cooler and wetter conditions. However, there is considerable uncertainty in how this system will evolve and, consequently, how much rain will fall and where.
Ensemble model clusters have diverged significantly and are now split nearly into thirds on the potential outcome:
- Scenario 1 (Driest): The system tracks in a way that brings light rain, but mostly dry in northwest Montana.
- Scenario 2 (Moderate/Targeted Rain): The system delivers modest and focused rainfall, primarily impacting north-central Idaho and west-central Montana.
- Scenario 3 (Widespread Rain): A more organized and slower- moving system provides beneficial, widespread rainfall across most of the forecast area.
Given this uncertainty, it is too early to pinpoint specific impacts, but residents should be prepared for the possibility of a cool and wet start to the work week.
Looking further ahead, model clusters support brief ridging the middle of next week followed by another trough impacting the region to end next week, suggesting the active, unsettled pattern may continue.
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.AVIATION...Early morning showers/thunderstorms continue in northwest Montana but they will gradually diminish as they push southward. Otherwise, areas of patchy valley fog and low stratus ceilings are possible, particularly at KGPI where considerable rain fell last evening. Weak ridging will help to suppress convection this afternoon compared to recent days. Although, lingering moisture and daytime heating will still allow for scattered showers and isolated thunderstorms, mainly terrain anchored, diminishing after sunset. VFR conditions are expected to prevail for most of the TAF period outside of any shower and storm activity.
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.MSO WATCHES/WARNINGS/ADVISORIES... MT...None. ID...None. &&
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NWS MSO Office Area Forecast Discussion