textproduct: Missoula

DISCUSSION

KEY MESSAGES:

- Cold temperatures through Monday

- Pockets of light valley freezing rain/pass level snow potential late this week

Cold temperatures persist as modified Arctic air remains entrenched across the Northern Rockies. Low-level stratus and occasional snow flurries have been slow to erode across Northwest Montana, making valley fog and stratus a primary concern through Monday. A weak disturbance will slide through the region on Monday afternoon, bringing extensive mid- level cloud cover and additional flurries; this cloud deck may keep afternoon highs several degrees cooler than guidance suggests.

High pressure ridging will build along the West Coast before leaning eastward into the Northern Rockies Tuesday and Wednesday. This stagnant pattern will heighten the potential for persistent valley fog and stratus, especially north of I-90. However, the ridge appears increasingly "dirty" from Wednesday into next weekend. This means several weak disturbances and remnants of an atmospheric river will bring rounds of cloud cover and light precipitation.

With cold air trapped at the surface and snow levels gradually rising aloft, there is a potential for light freezing rain or a wintry mix in the valleys, while light snow remains over mountain passes. While confidence in the specific timing and totals remains low, this period warrants close monitoring for localized travel impacts due to black ice during overnight and morning periods.

AVIATION

VFR conditions will prevail across most of the Northern Rockies through Monday under a steady northwest flow. The primary exception remains Northwest Montana, where persistent low-level moisture and strong valley inversions will maintain areas of low stratus, fog, and occasional snow flurries through Monday. Expect localized MVFR/IFR conditions in these basins, though some gradual improvement is likely each afternoon.

Mid-level cloud cover will increase region-wide on Monday afternoon as a weak shortwave passes through. While this may produce additional localized flurries, no significant accumulations or visibility reductions are expected at terminals. Overall aviation impacts remain low outside of the entrenched valley stratus in the north.

MSO WATCHES/WARNINGS/ADVISORIES

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