textproduct: Missoula

DISCUSSION

KEY MESSAGES:

- Frost possible each morning through mid week

- Slow warming trend with lingering showers, especially during the afternoon and evening

A broad upper level trough remains the dominant feature across the Northern Rockies, maintaining north to northwesterly flow through midweek. This regime will sustain unseasonably cool conditions and persistent shower activity across western Montana and north central Idaho. Diurnal clearing will facilitate efficient radiational cooling, pushing overnight lows below freezing for most valleys, while high-elevation terrain will likely drop into the low 20s. Within this flow, a series of subtle shortwaves will trigger isolated to scattered showers, with coverage and intensity peaking during the afternoon hours as modest instability develops. Activity should diminish rapidly after sunset each evening.

The synoptic pattern shifts significantly Thursday into Friday as an amplified ridge of high pressure builds over the region. This transition will initiate a robust warming and drying trend, with Friday's max temperatures projected to reach approximately 10 degrees above seasonal normals. While the ridge remains the primary driver, a weak disturbance traversing the Canadian border may introduce localized cloud cover and light precipitation across far northwest Montana Friday afternoon.

Looking into the weekend and beyond, long-term guidance continues to advertise a significant low pressure system impacting the Western U.S., though model divergence persists regarding its exact trajectory. Current ensemble models favor a more southerly track (80% probability), keeping the primary energy and deeper moisture well south of western Montana and north-central Idaho. Under this scenario, the region would likely see increased shower activity associated with the system's northern periphery, though high snow levels should mitigate any snow impacts.

AVIATION

North to northwesterly flow aloft will maintain a regime of diurnally driven shower activity across western Montana and north-central Idaho through midweek. Predominant VFR conditions are expected to prevail, though localized MVFR/IFR reductions in visibility and ceilings are possible within more robust afternoon showers, particularly over terrain where mountain obscurations may occur. Any convective activity will diminish rapidly after sunset as the boundary layer stabilizes. Surface winds will see the current easterly gradient gradually relax through the remainder of the morning hours, transitioning to a light and variable or terrain-driven flow by the afternoon.

MSO WATCHES/WARNINGS/ADVISORIES

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