You would be forgiven if you assumed the fall storm chase season was already done after a short/rapid burst in September and early October. And I’d be willing to forgive you for such things as well. The upper-air pattern has moved into something pretty unfavorable for severe weather in the middle of the country, but changes could be coming.

500wh conus 3

Currently, we are locked into strong northerly upper flow across the Plains with a ridge building over the Southwest. You’d be forgiven if you thought this was a model chart from this summer’s pattern — but it is truly what we have right now.

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Fast-forwarding a few days reveals not much appreciable change to the shape of the flow over the country, the only changes are the details of where the strongest flow is. This type of pattern results in milder/warmer and most definitely drier weather from the Southwest out onto the Plains.

A.K.A. — No severe weather.

500wh conus 5

But things begin to change this weekend, both the Euro and the GFS show the ridge over the Southwest flattening and a trough beginning to dig in along the Pacific coast.

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It is anybody’s guess what the eventual trough ejection would look like, the Euro and GFS disagree heavily on the smaller details, but both model’s ensemble versions do show a shift from a ridge (high pressure) to a trough (low pressure) in the western half of the U.S.

What All This Means

Simply put, we’re marching towards a big change in the upper-air pattern as we move into the back parts of October, and it is not unreasonable to think severe weather will follow at some point with this pattern. A couple of things that lead me to believe this are the expected anomalously warm temperatures over the Plains by this weekend, mixed with the Gulf of Mexico still showing unseasonably warm temperatures. 

Cdas sflux ssta watl 1

One of the basics of weather is warm air holds more moisture, and if there is already moisture-rich air to the south — it doesn’t take much more than a trough digging out west to funnel that rich, unstable air north. The Gulf did cool a bit the last week, but it’s still just at jet fuel levels of warm overall. 

The Fall season probably isn’t finished, and we may have the biggest event of the season yet somewhere in late October to November. It’s too early to say one way or the other. We’re keeping an eye on it.