Update on the threat for severe weather late this afternoon/evening

12:30 PM Thursday 9/16/2021

The atmosphere is becoming increasingly unstable in the Northland early this afternoon thanks to ample sunshine and a southerly wind which is transporting a warm, humid and unstable air mass northeastward into the Northland.

Meanwhile, a cold front was over northwestern Minnesota as of Noon today, and this boundary will move east into an unstable environment by later today. Forcing associated with that front should help erode a cap (warm temps aloft) causing showers and thunderstorms to develop in north-central Minnesota by late this afternoon.

We should see scattered showers and thunderstorms develop in north-central and east-central Minnesota by later today, in and near that yellow outlined area on the map — Storm initiation times still vary a bit in model data, but the most likely time frame for when storms develop would be from around 3 PM to 6 PM today in the aforementioned areas. Once storms develop they will move off to the east.

Scattered showers and thunderstorms should persist through early Friday morning especially from northeast and east-central Minnesota into all of northwest Wisconsin, but the threat for severe weather should diminish by late this evening.

Note: Shower and thunderstorm chances for Duluth and Superior increase after 7 PM tonight.

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Dew points have climbed into the low to mid 60s over much of northern Minnesota early this afternoon so we have the juice in the atmosphere for storms today.

Instability continues to build out ahead of an eastward moving cold front, and we should see some expansion of the highest CAPE (yellow and orange colors on map) a little farther east by late this afternoon.

Scattered strong to severe thunderstorms (Slight Risk/Yellow) are possible over all of northeast and east-central Minnesota late this afternoon and this evening. While isolated strong to severe storms (Marginal Risk/Dark Green) are possible across northwest Wisconsin this evening and overnight.

Primary hazards from storms that become severe later today include

Damaging Wind Gusts of 60 to 70 mph
Large Hail of 1″ to 1.50″ in diameter (Quarter to Ping Pong ball size)

Although a tornado can’t be ruled out in north-central, northeast and east-central Minnesota late this afternoon or early this evening, the overall risk for tornadoes is pretty low with this setup. The wind shear is certainly there (we have plenty of that) and we also have a very strong winds aloft, but we’re lacking deep moisture today, there’s enough for some severe weather, but probably not for tornadoes.

Note: The risk for severe storms is greatest mainly over north-central, northeast and east-central Minnesota with a lesser chance for severe weather in most of northwest Wisconsin.

Tim

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