MISSOULA — High pressure will lead to valley inversions this week. Right now, west-central and southwest Montana valleys have the best chance to see these inversions develop. For those stuck under the inversions, highs will struggle to get out of the 20s, while other locations warm into the 30s and 40s. The best example of this today is in southwest Montana where the Bitterroot Valley will see highs in the 20s to low 30s while higher elevation locations such as Butte, Anaconda, Philipsburg and Georgetown Lake will see temps in the 30s to low 40s.
As is the case with inversions, valley air becomes trapped and doesn't move much. This will lead to deteriorating air quality through the week. An Air Stagnation Advisory has been issued for the Missoula/Bitterroot Valleys along with the Seeley/Swan Valleys through 5 pm Friday.
We won't stay completely dry this week. Several weak systems will move through the ridge bringing clouds along with very light mountain snow along with valley rain/snow to parts of northwest Montana. However, very little to no snow accumulation is expected with these systems.