Meteorologist says, “It’s getting bigger” as this storm threat is about to expand

A developing severe-weather pattern is expected to begin across the Upper Midwest on Sunday before expanding sharply into the Great Lakes and Ohio Valley on Monday, placing roughly 30 million people in a corridor where damaging winds, large hail, and possibly tornadoes could become a concern.

Meteorologist Ryan Hall, host of the Ryan Hall, Y’all weather channel, said confidence in the setup has increased as forecast guidance continues to show a disturbance moving out of the Dakotas and riding along the eastern edge of a strengthening heat dome.

The threat is expected to begin with organized storm clusters across Minnesota and Wisconsin, then grow into a much larger risk zone that includes Chicago, Milwaukee, Indianapolis, Toledo, and Columbus as the system moves southeast.

Hall said the atmosphere may eventually support a large thunderstorm complex, commonly known as an MCS, capable of producing a long corridor of damaging winds from the Great Lakes into the Ohio Valley. He stopped short of predicting a derecho, but said the pattern was among the most supportive he had seen this year for a fast-moving and long-lived wind event.

Friday Brings an Early Severe-Weather Test

Before the larger Sunday and Monday event develops, Hall said parts of the northern Plains will face a more isolated but potentially intense severe-weather threat Friday evening.

A slight-risk area covers portions of North Dakota and northwestern Minnesota, including areas near Bismarck and Thief River Falls, where more than 2,000 joules of atmospheric instability may overlap with strong wind shear.

If storms are able to break through a layer of warm air above the surface, Hall said they could develop into supercells producing hail as large as golf balls and wind gusts approaching 70 mph.

There is also a small tornado risk, particularly near boundaries where winds and moisture come together, although Hall described the day as highly uncertain because the atmospheric cap could prevent widespread storm development.

That makes Friday a classic boom-or-bust setup. If the cap holds, only limited activity may develop, but if it breaks, the storms that form could become strong quickly and continue into north-central Minnesota after dark.

Hall advised residents to finish outdoor work earlier in the day and remain alert during the evening, since warm and humid air near the surface may continue feeding storms well after sunset.

The Friday threat is not expected to match the larger system forecast for Sunday and Monday, but it may offer an early indication of how much moisture and instability are available across the northern Plains.

Sunday’s Storm Corridor Targets the Upper Midwest

The broader severe-weather episode is expected to begin Sunday afternoon, when a disturbance moving out of the Dakotas encounters very humid air over Minnesota and Wisconsin.

Hall said the current severe-weather outline covers approximately 9.5 million to 10 million people from Minneapolis and Duluth southward through Madison, Green Bay, and Rockford, Illinois.

The main corridor may still shift because the forecast remains several days away, but Hall said the strongest signal currently extends from the Minneapolis area toward Green Bay, with Fargo positioned near the western edge of the threat.

Storms are expected to develop within a northwesterly flow pattern created by high pressure over the Plains and a disturbance moving around the eastern side of the heat dome.

That arrangement is common during the summer, but Hall warned that it can produce some of the Upper Midwest’s most powerful thunderstorm complexes when high moisture, strong instability, and favorable upper-level winds come together.

Forecast guidance suggests that the atmosphere may contain between 2,000 and 3,000 joules of storm energy, enough to support explosive development once the disturbance arrives.

Hall expects organized clusters to become the primary storm mode, with damaging winds posing the greatest widespread concern as storms move through Minnesota and central Wisconsin during the afternoon and evening.

Those winds could be strong enough to bring down trees, damage temporary structures, and send unsecured objects airborne. Campgrounds, festivals, and other large outdoor gatherings would be particularly vulnerable because people may have limited shelter and little time to react once a fast-moving line approaches.

Hall specifically raised concerns about visitors attending the EAA AirVenture event in Oshkosh, Wisconsin, which continues through Sunday.

He urged anyone camping at the event to monitor radar and warnings throughout the afternoon rather than waiting until the storm line is already approaching the grounds.

That is practical advice for any crowded outdoor event in the risk zone. The danger from severe wind is not limited to buildings and power lines, since tents, canopies, recreational vehicles, trees, and loose equipment can all become hazardous during a sudden gust front.

Monday’s Risk Expands Toward Chicago and Columbus

The storm system is expected to move south and east Monday, expanding the severe-weather corridor into a much more heavily populated section of the Great Lakes and Ohio Valley.

Hall said approximately 30 million people may fall within the broader risk area, including residents of Chicago, Milwaukee, Indianapolis, Toledo, and Columbus.

The same disturbance responsible for Sunday’s storms will continue diving southeast beneath an upper-level low near Hudson Bay, maintaining strong northwesterly flow over the Great Lakes.

What has attracted Hall’s attention is the expected timing and the possibility that storms could begin developing around Chicago as early as the middle of the afternoon.

As the afternoon progresses, a strengthening stream of warm and humid air close to the ground may help individual storms and clusters merge into a larger complex.

Hall said the low-level jet could become stronger during the evening and overnight, providing the energy needed to maintain the system as it pushes through the Great Lakes and later sinks toward the Ohio Valley.

The most likely hazard is damaging wind, with the strongest period currently expected from Monday afternoon into the evening. Hall described a possible line moving through Chicagoland or Indianapolis with enough force to knock down trees and leave entire suburbs without power.

The exact timing remains uncertain, and forecast models could shift the corridor or move the storms several hours earlier or later. Even so, Hall said his confidence had grown because instability and wind shear increasingly appear likely to overlap when the storm cluster reaches the region.

Overnight timing would make the event more dangerous, particularly for people who rely only on outdoor warning sirens or do not keep their phones nearby while sleeping.

Hall urged residents throughout the corridor to have a warning system capable of waking them if a destructive thunderstorm approaches after dark.

A Large Wind Complex Is Becoming More Plausible

Hall said the Monday setup could support an MCS, a broad and organized complex of thunderstorms that may travel across several states while producing repeated areas of damaging wind.

He also mentioned the possibility of a derecho, which is a long-lived and fast-moving windstorm that travels for hundreds of miles, although he emphasized that it remained too early to make such a prediction.

High-resolution models were not yet available for the event, meaning forecasters could not confidently determine whether storms would remain separate, form smaller clusters, or merge into one dominant line.

Still, Hall said the larger pattern was the most favorable he had seen this year for that type of widespread wind event.

That does not mean a derecho is certain, and the distinction is important because early forecasts often identify ingredients before they can accurately predict the final shape of the storms.

The most responsible way to view the risk is that the atmosphere may support a significant and organized damaging-wind event, while the precise intensity and length of the storm track will become clearer closer to Monday.

Milwaukee and the northern portion of the risk area remain firmly involved, while communities farther south toward the Ohio River Valley sit closer to the edge of the initial outlook.

If the storm complex holds together Monday night, those southern areas could still experience damaging wind and heavy rain after the main line crosses the Great Lakes.

Tuesday May Carry the Threat Into the Mid-Atlantic

After Monday, the remaining storm energy may continue southeast toward the central Appalachians and Mid-Atlantic, although Hall described Tuesday’s forecast as much less certain.

Washington, D.C., Baltimore, West Virginia, and surrounding areas currently appear to have their best severe-weather opportunity of the week on Tuesday, but the outcome will depend heavily on what happens during the previous two days.

The shortwave driving the Sunday and Monday storms is expected to move east while the main jet stream continues digging south, which may weaken the northwesterly push responsible for organizing the system.

If the storm complex survives that transition, Hall said damaging winds, heavy rain, and perhaps a tornado threat could remain possible from the central Appalachians toward the Mid-Atlantic.

If it weakens earlier, Tuesday may become more of a flooding event than a widespread severe-weather day.

That distinction is especially important for West Virginia, where additional storms could move into areas that have already experienced serious flooding.

Hall said a marginal flood risk was already in place for central West Virginia, and rainfall may begin there Monday night before the primary Tuesday threat develops farther east.

Residents from the West Virginia mountains through Washington and Baltimore should therefore treat Tuesday as a day to monitor closely, while understanding that the forecast may change considerably depending on the evolution of the weekend storms.

Flooding and Dangerous Heat Continue Elsewhere

While severe storms build in the Midwest, Hall said the Southeast will remain vulnerable to repeated flash flooding through Friday and into the weekend.

A stalled frontal boundary is expected to continue pulling deep tropical moisture into eastern Tennessee, western North Carolina, north Georgia, and the broader Carolinas, where rain may fall at rates of two to six inches per hour beneath the strongest storms.

The greatest concern is training convection, in which repeated cells move across the same communities while the ground is already saturated.

Hall said eastern Tennessee and western North Carolina were particularly concerning because mountainous terrain can funnel water rapidly into creeks, valleys, and low-water crossings.

A slight flood risk could be upgraded if the heaviest rainfall corridor becomes more certain, especially from north-central Alabama through north Georgia and into the Carolinas.

Farther west, the final moisture associated with Tropical Storm Bertha is expected to move inland across Texas, bringing locally heavy rain but little additional wind threat.

Hall said the system had remained weak and poorly organized, although an intense rain band near Corpus Christi or Brownsville could still produce localized flooding if it stalls.

At the same time, a major heat dome will continue strengthening across the southern tier, Great Basin, Plains, lower Mississippi Valley, Southwest, and California valleys.

Heat indices of 105 to 115 degrees are expected in some areas, while overnight temperatures may remain near 85 degrees, preventing the body from recovering after extreme daytime heat.

Hall described it as the most dangerous heat of the summer so far and said the pattern could continue through the end of July and possibly into early August.

The severe-weather threat may draw the most attention because of its expanding size, but the combination of flash flooding and prolonged heat could affect more people over a longer period.

By Sunday, the focus will shift toward Minnesota and Wisconsin, followed by a much larger Great Lakes and Ohio Valley threat Monday and a possible Mid-Atlantic extension Tuesday.

Hall said the exact boundaries and timing will continue to change, but the broader signal is becoming clearer: the storm corridor is expanding, confidence is increasing, and millions of people may need to prepare for several consecutive days of active and potentially dangerous weather.