MISSOULA — A system will bring scattered valley rain/snow showers and mountain snow to western Montana this afternoon. Very little to no snow accumulation is expected in the valleys. Lookout and Lolo Passes look to be hit hardest with 2"-to-6" possible. Marias, McDonald, Homestake and Lost Trail passes will also see some accumulating snow just to a lesser degree.
High pressure will build right back in Tuesday and continue through the rest of this week and even into the weekend. This time of year with the long nights, short days and low sun angle, conditions are perfect for valley inversions to develop. Under these conditions fog, deteriorating air quality and cold pools keeping some locations around freezing for high temperatures will all be possible.
Mountains on the other hand will be able to rise above the inversions leading to sunny and dry conditions all week.