Cold air and strong valley inversions are present across western Montana on Wednesday morning. The valley cold pools of air are due to a ridge of high pressure sitting over Montana. This ridge is creating light surface winds and limited vertical motion, leading to stagnant air in the valleys. Air quality in currently MODERATE in Seeley Lake, Frenchtown, Missoula, Hamilton, Helena, and Butte. Temperatures in these valleys are generally in the single digits, with ridgetop temperatures in the 20s. Up along those ridges, air movement is much better, with warmer temperatures and breezy conditions. Northwest Montana has fared better, with slightly warmer temperatures and weaker inversions. Air quality in northwest Montana is ranging between GOOD and MODERATE this morning.
Unfortunately, the ridge of high pressure causing the air quality concerns in the valleys is expected to continue impacting the region through Thursday. We are also seeing more widespread cloud cover today. These clouds are inhibiting the lifting of inversions in many locations. This is because the solar radiation from the sunlight helps to erode the cold air pools and promotes lifting. Without the sunshine, these inversions are going to be stubborn to break.
Conditions will be similar on Thursday, with the cloud cover keeping the inversions in place. For areas that do manage to break the inversions on Wednesday, the cloud cover may help keep overnight temperatures from dropping too far. For most valleys, however, lows in the single digits and teens are likely once again. Air quality on Thursday will likely remain MODERATE around western Montana, especially in Missoula, Hamilton, Helena, and Butte. Some of those areas may see hourly levels reach UNHEALTHY FOR SENSITIVE GROUPS at times, especially Thursday morning.
We should finally start to see improvement on Friday as warmer air attempts to push into the region. Most valleys should start to see improved air quality by Friday afternoon. There is a chance that particularly strong inversions may linger into Saturday. Beginning Saturday and lasting into next week, unsettled weather with widespread snow shows is expected as a trough of low pressure moves into the area. Air quality should improve for all locations for the weekend and into early next week.