September blowtorch – 90s to return to the Mid-South!

As I mentioned a few days ago here, the heat (if not the humidity) of summer will return after our weekend cooldown. Who to blame? You can actually blame the same Canadian high that will cool us down this weekend.

How a record-breaking cold Canadian high can produce summer-like heat just a few days later
Take a look at the 850 mb model data for Saturday morning. The zero C line is right over Chicago and the surface high is also nearby. Some of the colder suburbs will approach the freezing mark for lows Saturday morning, which is well below the records at O’Hare (40) and Rockford (37). The coldest morning in the Mid-South will be Sunday morning, where temperatures should fall below 50 in most places for the first time since May 21st.

By Sunday evening, a shortwave and a strong 110 kt jet streak at 200mb upstream of the trough axis will combine to carve out a deepening trough over the Pacific Northwest. This meridional flow will cause our record-breaking cold Canadian high pressure area to essentially park off the East Coast and the return flow of the high will create the blowtorch conditions. By Tuesday evening, synoptic conditions are perfectly set-up for a hot and dry pattern for the eastern 2/3 of the United States. Keep in mind that normals are dropping quickly and that by the middle of next week, the average high/low for the Mid-South is 80/57. Note the trajectory of the winds at 200mb, 500 mb and 850mb on Tuesday evening. All show a deep, consistent flow out of the desert Southwest. Even by Friday evening, a piece of the trough gets left behind in CA as a cut-off low and the broad southwesterly flow continues. It looks like the Tuesday-Thursday period will be in the 85-90 range with at least one day in the lower 90s. And this may be a low estimate. With our dry soil conditions (despite the rains of last weekend), mid-90s are not out of the question. There doesn’t appear to be any good rain chances out there through the ten-day period.

The hot and dry pattern is strongly evidenced by the ensembles and supporting model data. The Climate Prediction Center has the red bullseye squarely over the Midwest for both the 6-10 and 8-14 day periods.

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