Prompts winter weather advisories as cold air moves in Friday night

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Welcome to the nocturnal thunderstorm season in Minnesota.

Mid- to late July is prime time for overnight storms that can turn severe in Minnesota and the Upper Midwest. Potent warm fronts ride north into Minnesota in July. That means plenty of warm, humid air near the surface. Longer nights help cool the atmosphere aloft. 

That creates an unstable situation as steamy air near the ground rises quickly into the colder air aloft. The result is severe storms that can race across the Upper Midwest on July nights.

The weather maps this weekend look favorable for strong to severe storms to develop and sustain their intensity through the nighttime hours. Intense heat and humidity push north behind a steamy warm front Friday night into Saturday morning. A pool of dew points in the 70s pushes north Friday night to fuel the developing storms.

A strong southerly low-level jet stream around 5,000 feet above ground will feed developing storms and sustain the low-level inflow as the upper winds push them eastward. This warm moist low-level inflow is like the storm’s oxygen supply. 

NOAA’s NAM 3 km resolution model depicts intense storms in the Dakotas around 7 p.m. Friday night racing east into Minnesota. Note the bow-shaped morphology of the squall lines pushing east overnight. This is usually a damaging wind signature on the storms leading edge.

In this model forecast scenario, they reach eastern Minnesota and the Twin Cities around 5 a.m. Saturday.

The highest severe risk favors western Minnesota late Friday night. But if the storms sustain intensity overnight, we could see strong to damaging wind storms blow through the populous Twin Cities in the early hours Saturday morning.

The potential is there for another strong to severe line of storms Saturday night into early Sunday as cold front slices into Saturday’s hot, unstable air mass.

If the storms are well organized and sustained, they may produce damaging winds along the leading edge over long distances. In that event, we may have a derecho on our hands Friday night into Saturday morning. 

Be ready for possible severe nocturnal thunderstorm overnight this weekend.

Weather and Climate News

Updraft® - Minnesota Weather News

Paul Huttner

Author

A potent warm front may spawn some nocturnal thunderstorms this weekend. The risk for severe storms overnight is higher than usual.

NOAA

NOAA NAM 3 km model dew point forecast Friday evening

NOAA via tropical tidbits

NOAA 850 millibar wind forecast Friday night

NOAA NAM 3 km model 7 pm Friday to 5 am Saturday

Nocturnal thunderstorm, derecho severe weather threat this weekend

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