Inversion Forecast

Update 12/15/2025: Overview: This week's weather pattern should deliver a series of precipitation days across the northern half of the state starting midweek. As such, inversion impacts should be minimal as the unsettled weather sweeps through. Until then, weak inversions should linger and present moderate air quality conditions in northern valleys including the SLC valley but will likely break mid-week into the weekend. Over the long term, a flattening of the east Pacific Ridge this upcoming weekends portends the development of an offshore trough. Good model consistency in this general ridge replacement event through the holiday stretch. Short term: A few days of lingering, weak inversions driven by the diurnal surface inversion and the mid-level subsidence inversion will continue to some degree through midweek before the passing pattern presents precipitation percentages and should clear things out up north. Expecting the warm air and approximation to the unsettled weather to also help central and southern Utah inversions. Long term: With a ridge replacement predicted this weekend and early next week and the off shore trough of low pressure supplying our upstream weather conditions, the remaining forecast for the 2025 calendar year calls for minimal inversion conditions. Hemispheric momentum forecasts continue to call for higher amplitude patterns, which would tend to favor the familiar West Coast ridge of high pressure within the La Nina influence. As the upcoming trough replacement displaces the ridge into the central U.S., the end of the calendar year may see that ridge back up into the western U.S. Model agreement remains mixed on this scenario, but the CFSv2 model presented here has atmospheric heights increasing through the final days of 2025 and into the new year, and as such inversion conditions becoming more likely as a result.