textproduct: Missoula
This forecast discussion was created in the public domain by the National Weather Service. It can be found in its original form here.
DISCUSSION
KEY MESSAGES:
- Valley inversions through Thursday this week, with near normal temperatures. Areas of degrading valley air quality.
- Ridge breakdown by Friday, with risk for valley freezing rain.
A ridge of high pressure will continue to be the dominant feature over the Northern Rockies through Thursday. This ridge will keep strong valley inversions in place causing air quality to slowly degrade over the next 24 to 48 hours especially during the overnight hours. Fog and low stratus will also be an issue especially near rivers and large bodies of water.
A weak disturbance is still on track to push into the Northern Rockies from the southwest. This feature will be relatively warm for this time of year causing snow levels to be around 5500 feet during the onset of precipitation. The mountains will experience light snow accumulations but the valleys should anticipate a wintry mix of rain, snow and freezing rain. Freezing rain can cause road surfaces to become icy fairly quickly especially during the overnight into the morning hours. Precipitation types can change rapidly in short distances, especially between shaded and non-shaded valleys.
Weak disturbances will continue to move through the Northern Rockies through the weekend. Snow levels will remain high fluctuating between 4000 to 6000 feet. The valley inversions are anticipated throughout the weekend causing the threat of freezing rain to diminish.
AVIATION
A ridge of high pressure will continue to be the dominant feature over the region for the next 24 hours. Valley inversions will be strengthening tonight increasing the potential for fog and low stratus to develop especially near KMSO and KGPI by Wednesday morning. The Mission valley around Flathead lake will continue to experience a low stratus deck.
MSO WATCHES/WARNINGS/ADVISORIES
MT...ID...Air Stagnation Advisory until noon PST Thursday for Lower Hells Canyon/Salmon River Region...Northern Clearwater Mountains...Orofino/Grangeville Region...Southern Clearwater Mountains.
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