Forecast: Tuesday heat and severe threat

Get ready for a wild weather Tuesday.

Tuesday will feature excessive heat in much of southern Minnesota, and the threat for strong to potentially severe thunderstorms statewide.

Let’s start with the heat.

A hot, sticky air mass is surging north from Nebraska and Kansas. Temperatures reached the mid to upper 90s from Kansas into the Dakotas and eastern Montana Monday. The “thermal ridge” or heat core is likely to shift east and be in place right over southern Minnesota during the day Tuesday.

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One forecast technique yields high temperatures between 95 and 100 degrees in southern Minnesota, including the Twin Cities Tuesday!

I expect many locations will hit 94 to 96 Tuesday, and I wouldn’t be shocked to see a 100 degree reading somewhere in the southern half of Minnesota Tuesday around 5pm.

It’s the heat AND the humidity!

The one day heat wave will come with dangerous humidity levels. Dew points will surge toward 70 degrees.

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Some of the models hint at dewpoints approaching 75 degrees by Tuesday evening in the metro! That’s Amazon Jungle humidity folks. We generally feel that level of moisture in Minnesota only once or twice a year.

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Forecast modles push dew points into the oppressive 70s Tuesday. Note the delightful drop into the 50s by mid week!

We could see some areas hit what I call the 95/75 danger zone. That’s a temperature of 95 degrees with dew point of 75. That yields an oppressive heat index of 107 degrees. Minnesotans (or anybody else for that matter) are generally not equipped to cope with that intense level of heat and humidity. 95/75 is a rare combination in Minnesota.

Take care tomorrow as temperatures and humidity rise to rain forest levels.

Severe threat:

A Canadian cold front will bring welcome relief with cooler temps and much lower humidity by Wednesday. It will also be the trigger for strong to severe storms as it slices through the steamy unstable air mass over Minnesota Tuesday.

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Storms will favor the northern half of Minnesota during the day Tuesday, and then spread south into southern Minnesota Tuesday evening and overnight. I’ll be scanning new forecast model runs overnight to update timing, but right now looks like the highest probability window for severe storms in the metro will be between 7pm Tuesday evening and 1am Wednesday morning.

The potential is there for large “bow echoes” to develop Tuesday in Minnesota. These lines of storms can cause widespread straight line wind damage. Also, several factors are coming together to spawn a few big rotating supercell thunderstorms at the onset of Tuesday’s outbreak. The combination of heat, moisture and directional wind shear (winds verring from south to WNW with height) may cause storms to rotate. These storms have the potential to produce (hopefully only a few) tornadoes.

SPC has “risked” much of Minnesota Tuesday. Be alert for severe weather watches and warnings as the storms approach.

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Stay cool and keep an eye out for storms Tuesday!


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