Inversion Forecast

Update 12/08/2025: Overview: Last weeks warm storms have reset valley floors back to bare ground. This week, a strong ridge of high pressure centered over the West Coast will shut off the region's storm track. Well-above average temperatures and clear conditions are forecast through the work week and potentially as far as early next week before the next trough of low pressure is predicted to break down the ridge. Despite the unseasonably warm air in place and lack of snow cover, valley inversions and air quality issues to moderate degrees should be anticipated through the week. Short term: The ridge of high pressure will begin to stabilize the state's atmosphere through the next few days. Forecast vertical profiles suggest the overnight and early morning inversions should mix out, but the mid-level subsidence inversion associated with the ridge will remain in play through the extended forecast. As such, air quality should degrade, but through a deeper layer of the atmosphere, which should help buffer some of the high-impact conditions the state would see if colder air and snow cover were present in valley floors. Long term: By the weekend, model guidance diverges on the timing and evolution for an upstream trough to develop and flatten the West Coast ridge. Most of the international modeling suite predicts the ridge will persevere through the end of the weekend, albeit flattening as the northern Rockies re-open the door for a return of shortwave trough activity. However, the CFSv2 (which this website's tool is examining), has had several of the most recent runs producing a trough sufficient enough to erode the ridge several days earlier than it's predictive peers. Given the greater consensus for the persevering ridge, expecting the inversion conditions and impacts the state sees to be more likely to last through the weekend than not despite this tools CFSv2 optimism. A more confident set of guidance should begin to materialize Wed/Thursday. Looking farther downstream, a continued lack of significant storm activity is predicted for the southwestern region while the Northern Rockies storm track remains the consensus solution. The ongoing weaker northwesterly storm systems would remain in play, limiting major precipitation events, but also keeping long-lived temperature inversions from gaining a foothold.