Some Flow Slides South This Week

We could see a small chance of severe storms on the C/S Plains.

A ‘cold front’ will slide south this week, riding cyclonic flow around a prominent ridge in the Western U.S. These two factors should increase shear and lift, leading to a chance of some severe storms as soon as Wednesday/Thursday this week.

This weak flow around the eastern edge of the ridge is a classic signal of an increased risk of severe storms, with shear increasing just enough to support some storm organization.

Currently, the GFS has some scattered storm coverage across the Central U.S. on Thursday evening. I suspect parts of our region will see a marginal risk during that timeframe, but the tornado risk will remain very low.

Ridge Reasserts Itself

This slight break in the action will not last long, as the Western U.S. ridge will reassert itself further east, shutting off the upper flow and increasing subsidence across the Plains into this weekend. This will also, not surprisingly, bring temps up a few degrees.

The ridge should reassert itself into early next week, pushing the jet stream north and east away from the Plains.

Long Term

There remains a consistent signal of a large-scale pattern change by the last 1/2 of the month, with the ridge tending to flatten out on ensembles and climo models as we head into October. This is pretty seasonal and, thus, not unexpected. It also tends to bias me because it looks like it should be for this time of year.

This graphic shows the heights of the mid-levels of the atmosphere. Anywhere you see orange or red, the heights are above average and tend to show more tendencies towards ridging; blues are troughs with a tendency towards more stormy weather.

The Euro weeklies show a significant trend towards flattening out the western U.S. ridge by the last week of September. If so, game on for more storm chasing.

Overall, the Western U.S. ridge that has dominated our weather for the last few months should weaken into the fall. This will provide an opportunity for a more favorable pattern for severe thunderstorms and our prototypical fall season. But, as with most fall severe weather seasons, it will likely be short-lived and pretty fast. When the seasons change, they really tend to change this time of year.

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