Much of northern Idaho, northwest Montana, Seeley Lake and Blackfoot Valley regions, and the Missoula area are under an Air Stagnation Advisory today, meaning low air quality, temperatures in the 20s and 30s, and the possibility of ice.
If you're driving through elevated areas, watch for low-lying fog on the road.
Air stagnation occurs when an air mass hovers over an area for a long time, producing a bowl-like effect, particularly in valleys. Until the next weather maker comes in and pushes the air mass out, pollutants can collect in the air over valley towns as people burn wood or other heat sources.
Luckily, the next air mass should arrive sometime next week, but until then, if you live in an area effected by valley inversion, you can expect the air quality to degrade until then.
The good news is that next week should also bring us Montanans some much-needed precipitation.