Inversion Forecast

01-27-2021 12:16:36 pm MST

Update 01/27/2021: Synopsis: The active weather for the state this week has kept inversion concerns off of the proverbial radar while precipitation arrives on the actual weather radar. The active weather pattern remains over the west for the short term while the long term forecast keeps odds for any strong, long-lived high pressure events on the lower end. Sub-seasonal forecasts show mid-February as the window of time when persistent inversion conditions will return however can't rule out some shorter inversion events peppered into the early February forecast. Short-term (Jan 27- Jan 30): The mean trough of low pressure parked over the west coast states will keep Utah's skies active and inversion-free through the last weekend of January. There are chances that micro inversions could develop across eastern and southeastern Utah Thursday and into early Friday, but the impending storm system forecast to sweep through the region Friday and Saturday will make quick work of any inversions that do develop. Long-term (Jan 30 - mid February): Long range forecast models continue to keep the large ridge of high pressure parked well off the west coast leaving an active pattern for the western U.S. states. As the weekend storm system ejects Saturday, a ridge is forecast to develop just to our east Sunday into Monday. With fresh snow in place, the position of the ridge will matter regarding whether weak, short-lived inversions set up across eastern Utah or not. Can't rule them out entirely, but any inversions that do develop should quickly erode by early week as the next storm system begins to encroach on the intermountain west. After this, the next sign of a western U.S. ridge is forecast for superbowl sunday with a long-lived situation forecast by mid-february.

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.