textproduct: Missoula

DISCUSSION

KEY MESSAGES:

- Slick travel continues into this evening in southwest Montana and Lemhi County, mainly above 4500 to 5000 feet.

- Strong Winds Late Sunday into Monday, with a 50 to 75 percent chance of widespread gusts over 40 mph in the valleys.

- Active Pattern for the rest of next week; potential for more wind and winter weather impacts

Widespread light to moderate precipitation continues across southwest Montana and Lemhi County this afternoon as moisture wraps around a slow-moving surface low. Slick roadways have been reported above 5,000 feet, particularly south of I-90. While overall precipitation is expected to diminish this evening, a backdoor cold front moving southwest out of central Montana may enhance mountain showers along the Continental Divide through 9:00 PM. Homestake and MacDonald Passes remain the primary areas of concern for additional light accumulations. Current Winter Weather Advisories remain in effect, with extensions possible depending on afternoon radar and observational trends. Travelers should anticipate winter driving conditions on all high-elevation routes through this evening.

Active northwest flow will persist through Saturday, though impacts are expected to be minor. Periodic showers will continue, but snow levels rising toward 5,000 feet and modest precipitation totals will limit accumulations to the mountains and passes. Breezy conditions are anticipated each afternoon, with westerly gusts of 20 to 30 mph common in valley locations.

Confidence remains high for a transition to a more impactful weather pattern beginning Sunday. An atmospheric river will initially target northwest Montana before shifting southward as a potent cold front crosses the region on Monday. While this front will drop snow levels to valley floors, wind is currently the primary hazard. Ensemble guidance indicates a 50 to 75 percent probability of valley gusts exceeding 40 mph across western Montana. In north central Idaho, these higher probabilities are largely confined to the Grangeville area (60 percent). Additionally, a favorable synoptic setup for mountain wave activity suggests localized gusts over 50 mph are possible Sunday afternoon through Monday morning. Wind highlights are likely in forthcoming shifts, as concerns grow for difficult travel for high-profile vehicles and potential damage to tree limbs.

The active pattern is projected to continue late next week as additional weak to moderate atmospheric rivers penetrate the Northern Rockies. The Climate Prediction Center guidance for the March 12th through 15th timeframe highlights a 20 to 40 percent chance of both high winds and heavy snow. While significant model variance regarding snow levels limits specific valley floor accumulations at this lead time, the period warrants close monitoring for renewed winter weather impacts.

AVIATION

Widespread light to moderate precipitation continues across southwest Montana and Lemhi County this afternoon, maintaining a mix of MVFR and IFR conditions due to low ceilings and reduced visibility in snow. Mountain obscurations will remain a primary concern, particularly south of I-90 and along the Continental Divide, as moisture wraps around a slow-moving surface low. While overall shower activity is expected to diminish this evening, a backdoor cold front moving southwest out of central Montana may briefly enhance mountain showers and lower ceilings near Homestake Pass, MacDonald Pass and KBTM through 06/04z. The rest of western Montana and north central Idaho will see continued showery conditions, mainly contained to the higher terrain. However, periodic rain and snow showers may lower into valleys later this afternoon and evening, bringing brief periods of MVFR ceilings/visibility for terminals such as KGPI, KMSO and KHRF.

Enhanced boundary layer mixing will result in westerly surface gusts of 15-25 knots, primarily affecting valley terminals through this afternoon. Expect these winds to diminish after 06/0200Z as the boundary layer decouples.

Looking into Friday, an active northwest flow will persist, bringing periodic VFR/MVFR showers and rising snow levels climbing toward 5,000 feet. Expect breezy conditions by afternoon, with westerly surface gusts of 15 to 25 kts common at valley terminals and potential for light to moderate mechanical turbulence over the ridges.

MSO WATCHES/WARNINGS/ADVISORIES

MT...Winter Weather Advisory until 3 PM MST this afternoon for Butte/Blackfoot Region.

ID...None.