3 Things To Know
- Severe storms are possible Thursday: Parts of Wisconsin are under a Level 2 of 5 Slight Risk, with the greatest concern during the afternoon and evening.
- Some storms could pack a serious punch: The strongest storms could produce hail larger than 2 inches, wind gusts over 75 mph and possibly a couple of tornadoes across the broader Upper Midwest.
- Exactly where storms develop remains uncertain: Morning storms and a strong atmospheric cap could influence what happens later, but if storms break through, supercells or a damaging line of storms could develop.
Parts of Wisconsin are under a Level 2 of 5 severe weather risk Thursday as another round of potentially powerful thunderstorms targets the Upper Midwest.
The Storm Prediction Center has placed portions of Wisconsin and the Upper Midwest in a Slight Risk, or Level 2 of 5, for severe thunderstorms Thursday, Sept. 3.
While there remains considerable uncertainty over exactly where storms will develop, the atmosphere could become extremely unstable. Any storms that are able to form and tap into that instability could become intense.
The primary threats will be large hail and damaging wind, although a couple of tornadoes also cannot be ruled out across the broader Upper Midwest.
Very Unstable Air Expected
Warm, humid air will continue to spread across the region Thursday as a warm front lifts north through the Upper Mississippi Valley and Upper Midwest.
The SPC expects a plume of steep midlevel lapse rates to develop above the humid air near the surface. That combination could produce an exceptionally unstable atmosphere by Thursday afternoon.
Forecast mixed-layer CAPE values could reach 3,000 to more than 4,000 joules per kilogram, indicating plenty of energy available for thunderstorms.
At the same time, approximately 40 to 50 knots of deep-layer wind shear could help storms become organized.
That combination of instability and wind shear could support both supercells and bowing lines of thunderstorms if storms are able to develop.
Large Hail, 75+ MPH Winds Possible
The SPC specifically highlights the potential for unusually intense severe weather with the strongest storms.
Potential hazards include:
- Hail larger than 2 inches in diameter
- Severe wind gusts exceeding 75 mph
- A couple of tornadoes
- Frequent lightning and torrential rainfall with stronger storms
The SPC expanded its 15% large hail risk into portions of Wisconsin with its Wednesday afternoon update because of the potential for significant hail.
Storms could initially develop Thursday morning from portions of the Missouri Valley into the Upper Midwest. Some of those storms could already produce isolated large hail before spreading east toward the Upper Great Lakes.
Afternoon and Evening Storm Development Uncertain
One major question is what happens after any morning thunderstorms move through.
A layer of warmer air aloft, known as a “cap,” could temporarily suppress additional thunderstorm development. Forecast models currently disagree on exactly where storms will be able to break through that cap Thursday afternoon and evening.
That makes the location and coverage of the most intense storms uncertain.
However, if thunderstorms do develop in the highly unstable air, conditions could support rapidly strengthening storms capable of producing significant severe weather.
The SPC noted that an upgrade to a Level 3 of 5 Enhanced Risk may eventually be necessary, particularly if confidence increases in the development of an organized thunderstorm complex capable of producing widespread damaging winds.
What Wisconsin Should Watch
The details of Thursday’s severe weather threat will become clearer as shorter-range forecast models get a better handle on where morning storms develop and how much instability can rebuild afterward.
For now, people across Wisconsin should keep an eye on the forecast, particularly if they have outdoor plans Thursday afternoon or evening.
The important takeaway is that not everyone will necessarily see severe storms, but storms that do develop could become particularly strong.
Check back with Wisconsin Weather Now Live Feed as we continue to track Thursday’s severe weather potential.
