A highly unusual setup is developing across the upper Midwest today as a powerful low-pressure system takes aim at the region.
The risk for severe thunderstorms remains highest from portions of south-central to eastern Minnesota into west-central Wisconsin late this afternoon and this evening, but at least an isolated severe threat may develop as far north as northwest Wisconsin, west toward Duluth, Moose Lake, Hinckley and Pine City in eastern Minnesota.
The main severe weather threats through this evening include damaging winds of 60 to 70 mph with gusts >80 mph possible along with a few tornadoes, with a strong tornado or two possible.
Categorial Severe Weather Risk from the Storm Prediction Center
Red: Moderate Risk
Orange: Enhanced Risk
Yellow: Slight Risk
Dark Green: Marginal Risk
Light Green: Non-Severe Storms
A 984 mb surface low was located over southwest Nebraska early this afternoon. The area of low pressure will continue to lift NE while deepening further as it moves into Minnesota this evening.
The air mass ahead of this system is very warm and humid with temperatures in the 60s and 70s with dew points in the 50s to lower 60s, meanwhile NW of the low we have much colder temperatures in the teens as far east as the western Dakotas early this afternoon.
A very strong low-level jet upwards of 60-70 knots across the Central Plains will continue to advect higher amounts of instability currently over the Central Plains NNE into parts of Minnesota and Wisconsin through this evening.
The first Tornado Watch of the day has been issued for parts of southern Minnesota, Iowa, Nebraska, Kansas and Missouri until 8 PM this evening.
A few additional watches may be issued farther NE through this evening.
Rain along with some thunderstorms is forecast to become more widespread in northeast Minnesota and northwest Wisconsin this evening, especially after 6 PM.
For Duluth — Thunderstorm potential is highest from ~8 PM to 11 PM tonight.
Expect heavy downpours and occasional lightning with the storms this evening, with damaging wind gusts possible as well, mainly from eastern Minnesota into northwest Wisconsin.
Here’s the Updraft Helicity Swath forecast ending at Midnight tonight — This tool can help determine where rotating thunderstorms may occur represented by the colored areas on the animation below, but this doesn’t guarantee there will be tornadoes everywhere a helicity swath is shown on this forecast loop. Either way it’s insane to even be seeing helicity swaths showing up in model guidance this far north in mid-December!