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    Inversion Forecast


    Discussion Last Updated: 01-18-2018 11:29:00 am MST

    Update 1/18/2018 Synopsis: A period of active weather will help drive a well-mixed atmosphere minimizing valley inversion ingredients through the end of the month. A return of more persistent regional high-pressure ridging will boost chances for modest (but short-lived) inversions through the month of February during the stretches of time when the high pressure does pass over. However, long-term seasonal forecast models remain optimistic that our inversion season might remain in the much-appreciated low end. So far, 2018 has avoided the accumulating valley snowpack and arctic air outbreaks, which helps mitigate inversion intensity during favorable large-scale forcing scenarios. With a predominant amount of low-elevations now completely bare ground, the local-scale inversion ingredients should continue to remain minimal. Entering a more progressive stretch of weather for the region, temperatures will be key to controlling when/if snow falls and how long it sticks around. Seasonal temperatures continue to look to remain above-average which will only help reduce the local snowpack driver of strong inversions. While the seasonal inversion outlook is promising, a non-negligible number of individual seasonal forecast model solutions point to periods of strong inversions meaning plenty of time remains for the large-scale and local-scale mechanisms to team up to create inverted air conditions. Forecaster: JDM

    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.