Strong to severe storms Tuesday; southern Minnesota tornado watch

Flood watch posted for the eastern half of Minnesota

SPC 1140 update
Severe weather outlook for Tuesday into Tuesday night
National Oceanic and Atmospheric Administration, via Iowa State University

Updated 1:22 p.m.

Waves of scattered showers and thunderstorms will lead to significant rainfall and severe weather potential later in the day Tuesday. A tornado watch was posted Tuesday afternoon for much of southern Minnesota, including the southern Twin Cities region.

tornado watch southern minnesota may 21 2024
A tornado watch is on Tuesday for much of southern Minnesota, with the National Weather Service describing it as a "particularly dangerous situation."
National Weather Service Storm Prediction Center

The National Weather Service described the watch conditions as a “particularly dangerous situation.” That means the threat of violent EF2 to EF5, long-track tornadoes exists.

Stormy setup Tuesday into Tuesday night 

A flood watch is posted for the eastern half of Minnesota through Tuesday night due to significant rainfall potential.

flood watch
Flood watch Tuesday into Tuesday night
National Oceanic and Atmospheric Administration, via Pivotal Weather

Severe storms are starting to develop near Omaha, Neb., near the center of an intense surface low pressure. That area is lifting northeast and skies are rapidly clearing out ahead of it, causing the atmosphere to destabilize in northern Iowa and southern Minnesota.

Those storms will continue to develop and track northeast into Minnesota Tuesday afternoon and evening.

prec 12p
Forecast precipitation 12 p.m. Tuesday through 4 a.m. Wednesday
College of DuPage weather lab

There’s a moderate (level 4 of 5) and enhanced risk (level 3 of 5) of severe weather Tuesday into Tuesday night for portions of southeastern Minnesota, bordered by a slight risk (level 2 of 5) area that includes the Twin Cities.

SPC 1140 update
Severe weather outlook for Tuesday into Tuesday night
NOAA Storm Prediction Center, via Iowa State University

The biggest risk is for tornadoes, damaging winds and large hail in some storms. 

We’ll have lots of dynamics to organize storms into severe thunderstorms. Notably, we’ll have a lot of shear — winds shifting direction and speed with height that rotate thunderstorm updrafts.

winds TUE
Surface and mid-level winds Tuesday late afternoon
NOAA, via Pivotal Weather

The key factor to watch is how much the atmosphere destabilizes. Most models put the most afternoon energy potential known as CAPE or or convective available potential energy into southeastern Minnesota.

Surface-based convective available potential energy, 4 p.m. Tuesday forecast
NOAA, via Pivotal Weather

Where shear and instability come together we measure something called the significant tornado parameter.

sig tor TUE
Forecast significant tornado parameter for 4 p.m. Tuesday
NOAA, via Pivotal Weather

The other forecast concern is heavy rainfall and potential flooding. Significant rainfall on top of already-saturated ground will be a concern. Many areas will receive a widespread 1 to 3 inches of rainfall, but several inches could fall in some places.  

QPF 24 6a
Forecast rainfall totals through early Wednesday
NOAA, via Pivotal Weather

Heavy rains could lead to increased flooding risk. River levels will continue to rise into the holiday weekend.

Excessive rainfall potential Tuesday into Tuesday night
National Weather Service

In addition to the severe weather threat, the storm system itself will generate high winds in western Minnesota with gusts potentially over 50 mph late Tuesday.

wind TUE adv
High winds forecast for western Minnesota Tuesday
National Weather Service

Calmer Wednesday with more rain Friday

Clouds and showers will linger into the start of Wednesday, especially north, along with cooler temperatures for most. Southern Minnesota will see more sun and warmer temps.

wed hi
Forecast highs Wednesday
National Weather Service

More rain is likely Friday into Friday night.

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