textproduct: Missoula

DISCUSSION

KEY MESSAGES:

- Localized light rain and mountain snow showers across north- central Idaho and southwest Montana Sunday afternoon into Monday.

- Widespread precipitation arrives Wednesday with snow levels initially around 5,000 ft.

An upper-level ridge will maintain dry conditions and lighter winds across the Northern Rockies today. Diurnal heating under mostly clear skies will push lower valley temperatures into the 40s and low 50s. Confidence is increasing in a subtle pattern shift for the southern half of the region Sunday into Monday. Ensemble clusters have converged on a solution where a warm front clips north-central Idaho, Lemhi County, and southwest Montana. This feature will introduce mid-to-high level cloud cover and a 30-40% chance of light precipitation starting Sunday afternoon. Expect light rain in the valleys and minor snow accumulations confined to the highest peaks, with minimal impacts anticipated. Locations north of Interstate 90 will remain dry and mild through this period.

Ridging peaks on Tuesday, likely marking the warmest day of the week. Mid-level moisture and cloud cover will increase from the west late Tuesday ahead of a pattern transition. A transient Pacific trough is projected to cross the region Wednesday into Thursday, a solution supported by approximately 85% of ensemble members. This system will transition the airmass to a more active regime, bringing widespread rain and snow showers. Initial snow levels near 5,000 feet will fall to valley floors by Thursday morning following the cold frontal passage. Breezy westerly winds will re-emerge, particularly along the Continental Divide and terrain-exposed locations.

Unsettled northwest flow will persist Friday into the weekend as the region remains on the periphery of the departing trough. While high-impact storms are not currently evident, embedded shortwaves will maintain orographic snow showers for the mountains. Looking further ahead, long-range teleconnections suggest the potential for an Arctic intrusion during the second week of March; however, significant spread in model timing and magnitude limits confidence at this lead time.

AVIATION

VFR conditions will prevail at all regional terminals (KMSO, KGPI, KBTM, KSMN, KHRF) through the next 24 hours. High pressure will maintain light, terrain-driven surface winds and high-level cirrus. By Sunday morning, patchy fog is possible in the more sheltered valleys of north-central Idaho and northwest Montana, though terminal-specific impacts are not anticipated. On Sunday afternoon, a clipping warm front will increase mid-level cloud decks across north central Idaho and southwest Montana. Ceilings are expected to remain VFR, though localized MVFR is possible near KSMN in north-central Idaho and Lemhi County as light rain and mountain snow showers develop.

MSO WATCHES/WARNINGS/ADVISORIES

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