Widespread showers and seasonably cool temperatures will persist across the Northern Rockies through Tuesday morning. Expect high temperatures generally in the 50s and 60s by Monday for most valleys, which is 10-20 degrees below normal for early September. Scattered showers and thunderstorms will develop on Saturday and Sunday, bringing the potential for brief heavy rain, lightning, small hail, and gusty winds of 25 to 45 mph. The heaviest and most widespread rain will arrive later Sunday into Monday as an upper low moves through the region. Most locations have a high probability of seeing at least a half-inch of rain from Sunday morning through Tuesday morning. There is a 60% chance for areas in Northwest and West-Central Montana to see MUCH higher totals of over 2 inches of rain.