Inversion Forecast
Update 11/03/2025: Welcome to November and the first inversion forecast discussion of the new season! Overview: The Aleutian Low presents the driving force behind episodic weather events passing through the Western U.S. While limited precipitation action is expected to move through Utah, the active regional pattern does translate to limited prolonged inversion expectations. Keep in mind that this statistical tool doesn't capture short term inversion events but without snow cover and more winter-like temperatures in place, concern for these type of events remains low. Short-term (Mon. Nov 3 - Friday Nov 7): Over the short-term forecast period, weak high pressure will keep temperatures elevated and precipitation chances limited. By mid-week, a weak setup should bring a bit more energetic weather conditions to northern Utah. Both sides of this week's weather coin shouldn't present any tangible inversion impacts. The initiation of our inversion season is unsurprisingly limited in inversion expectations. Long-term (Weeks 2-3): Beyond the end of this week, deviations across inter-model comparisons regarding the presence of more long-winded high pressure events begin to appear. GFS guidance develops a rather strong ridge of high pressure this upcoming weekend and early next week, so keeping an eye on the evolution of the end-of-week weather pattern. Global hemispheric momentum in the CFSv2 model weakens through mid-November, suggesting a longer-wave pattern as the jet stream and the translation of weather patterns pumps the brakes. Ridging patterns in the west would eject slower, so odds would increase for inversion conditions should a ridge develop and drop anchor in the West. However, without snow cover and more winter-like temperatures, inversion depth will be higher and valley airsheds more voluminous than such an event would produce later in the winter season. Concern for impact remains limited.
This product is being developed by researchers at the Utah Climate Center. Using output from the National Center for Environmental Prediction’s (NCEP) Climate Forecast System (CFSv2), this technique projects surface inversion probability for persistent inversion events—defined as events lasting longer than 4 days—with a demonstrated “skill” over a span of ~ 30 days. A surface inversion probability of 35% or greater suggests a statistically significant likelihood of an extended event. It should also be noted that inversion forecasts, in and of themselves, are not air quality projections. The projection is valid for a radius of roughly 200 miles around Salt Lake City.
Image Interpretation: The blue bar graph shows the calculated Surface Inversion Probabilities. Values above the horizontal yellow line (~35% on the right axis) have a statistical significance of manifesting as persistent (> 4 days) inversion events. The solid black line above the SIP chart shows the ensemble average of 200mb geopotential heights for the most recent 16 CFSv2 forecasts. The individual dotted lines are individual model runs. The vertical red and yellow lines identify the initialization (+0) and 30 day (+30) locations. SIP values lying within this 30 day window have a statistically significant confidence interval. Values before the initialization data are obtained from NCEP reanalysis data.
For more information on the methodology and origins of this product, see the following publication here.