Inversion Forecast
Update 01/08/2024: Summary: Mid-week clearing conditions have introduced weak inversions across the state but have remained weak enough to limit sensible impacts to air quality. While a late-week stretch of high pressure ridging is forecast, the overall active weather pattern remains in place, however, meaning expectations for meaningful inversions remain tabled for the time being. Short-term (Jan 09 - Jan 10): Incoming high pressure will place the state in a state of clearing conditions, but the limited residence time of the ridge of high pressure, whose focus remains upstream of Utah, means inversion impacts should remain low. The ongoing theme for the season continues to be quick transitions between short-lived high pressure and weak storm systems, helping undermine any major inversion events. Long-term: (Jan 11 - Mid January): Another pair of light-hitting storm cycles is forecast to pull through the region through the extended forecast, but one area of interest is the building ridge of high pressure by mid January, which could present a more meaningful inversion event. At this time, a cut-off low pressure system is paired with the stronger ridge of high pressure, with this cut-off low predicted to remain to Utah' south and west. The dance between the two features, and the ultimate position of the cut-off low pressure will be the determining factor in how the large-scale weather pattern either strengthens inversion conditions for Utah, or limits them. For the time being, northern Utah would be the most likely to see impacts, with the low pressure's southerly placement. THese features can quickly reposition themselves in forecast outcomes, so attention will remain on this mid-January pattern.
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.