textproduct: Missoula

DISCUSSION

KEY MESSAGES:

- Unsettled start to the week: Light valley rain, localized black ice, mainly northwest Montana. Light snow on Lolo, Lookout and Marias passes

- Mid week ridge: Warmth and stagnant pattern

- Pattern Shift on the Horizon (Feb 8-10): Increased precipitation chances

Occasional showers linger early this morning with snow levels hovering near 4500 feet. A localized slick commute is possible across northwest Montana (particularly in the Glacier Region) where light rain falling on sub-freezing roadways may result in pockets of black ice. Passes such as Lolo, Lookout, and Marias may also see brief snow cover. Otherwise, expect shower activity to taper off by sunrise, leaving behind slightly cooler temperatures today compared to Sunday.

A fast-moving disturbance arrives by mid-afternoon with scattered showers primarily in the terrain. Snow levels remain near 4500 feet, with light precipitation continuing into early Tuesday. Overall impacts remain minor, with snowfall accumulations generally limited to less than an inch over the passes.

High pressure ridging amplifies significantly from Tuesday through Saturday, bringing a return to unseasonably warm temperatures. Highs could challenge daily records Wednesday through Friday. However, this stagnant ridge pattern is a textbook setup for valley inversions; fog and stratus will likely expand over time, particularly across northwest Montana. Consequently, valley high temperatures in these trapped basins of northwest Montana may struggle to realize their full potential, likely verifying on the cooler side of guidance.

Looking ahead, ensemble guidance strongly (about 85% of ensemble clusters) signals a pattern shift beginning around February 8-10th. Evidence supports the ridge breaking down in favor of an upper- level trough digging along the West Coast. This transition would open the door for increased precipitation chances and a downward trend in temperatures.

AVIATION

Residual mountain obscurations, scattered showers, and gusty ridgetop winds will linger through early morning before tapering off by sunrise as the departing shortwave exits the region. Patchy valley fog may pop up this morning, particularly within the valleys of northwest Montana.

Widespread VFR conditions are expected to prevail by mid morning as skies partially clear. However, a secondary weak disturbance embedded in northwest flow arrives by mid-afternoon. Expect ceilings to lower as mid-level clouds thicken, bringing a return of scattered terrain-based showers and renewing mountain obscurations through Tuesday morning. Ridgetop winds will re- intensify with this system, likely inducing mechanical turbulence and occasional gusts of 15 to 20 kts surfacing at valley terminals this afternoon and evening.

MSO WATCHES/WARNINGS/ADVISORIES

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