textproduct: Missoula

DISCUSSION

KEY MESSAGES:

- Valley fog tonight into Thursday morning for Northwest Montana. - Warming and drying trend Friday through Sunday. - Increasing westerly winds and potential Monday afternoon storms as a weak disturbance flattens the ridge.

- Strong high pressure re-establishes late next week, maintaining a prolonged warm and dry pattern. Tonight-Thursday: Over the past 24 hours, a weak atmospheric river brought widespread precipitation to areas north of the Highway 12 corridor, with a band from Noxon to Logan Pass picking up between 0.50 and 1.00 inch of rain. The increased low-level moisture combined with light winds will likely promote valley fog development tonight into Thursday morning. High-resolution guidance continues to show a weak disturbance brushing northwest Montana Thursday, which could produce another round of light showers or sprinkles with accumulations generally limited to a few hundredths of an inch.

Friday-Sunday: An upper-level ridge of high pressure will build across the Northern Rockies Friday through Sunday. This pattern will bring a distinct warming and drying trend across all valleys and terrain through the weekend.

Monday-Next Week: Long-range guidance indicates a weak disturbance sliding east along the Canadian border Monday into Tuesday, temporarily flattening the upper ridge. This system will lead to an uptick in westerly winds across the Northern Rockies. A few models also suggest sufficient destabilization for isolated thunderstorm development by Monday afternoon. Once this disturbance clears out, a strong ridge of high pressure will re- build over the region for the remainder of next week and potentially even longer, prolonging warm and dry conditions.

AVIATION

Periodic mountain obscurations will present the primary aviation hazard along the I-90 this afternoon as a weak moisture plume sags southward. Valley fog and low stratus present the primary aviation hazard overnight into Thursday morning, particularly for northwest Montana (including KGPI) where 0.5 to 1.0 inch of rain fell over the past 24 hours. Localized MVFR/IFR conditions are possible in fog-prone valleys through mid- morning Thursday. Additionally, light showers or sprinkles may brush northwest Montana terminals on Thursday. Widespread VFR conditions and light, diurnally driven winds will return Friday as high pressure builds.

MSO WATCHES/WARNINGS/ADVISORIES

MT...None. ID...None.