A powerhouse cross-country storm is raising the threat of a severe thunderstorm outbreak while also dumping feet of snow

By Meteorologist Mary Gilbert, CNN

(CNN) — The potential for a multiday outbreak of severe thunderstorms is climbing as a massive, powerful storm tracks across the United States.

This storm has everything: feet of snow and blizzard conditions for parts of the Midwest and Great Lakes, roaring winds capable of knocking out power and elevating fire weather concerns in the Plains and Rockies, and thunderstorms that could unleash tornadoes and widespread damaging wind gusts.

The storm’s snowy side packed the most significant punch early Sunday for millions in the north-central US, with wind-whipped snow creating dangerous travel. But from late Sunday through Monday, more than 100 million people in the eastern half of the country will face an increasingly severe thunderstorm risk.

A Level 3 of 5 risk of severe thunderstorms is in place from the Great Lakes to the Gulf Coast on Sunday, with most storms expected to fire up late Sunday afternoon or evening and continue overnight into Monday.

Damaging straight-line wind gusts past 60 mph are the most widespread threat with any severe thunderstorms through Sunday night. Some areas from the Tennessee Valley into the Great Lakes could see even stronger gusts of 75 mph or more as storms start to congeal into a damaging line.

As of 5 p.m. ET Sunday, there were around 358,000 customers without power across seven states, according to the tracking website PowerOutage.US, including 87,000 in Ohio and 43,000 in Texas.

Tornadoes are also possible from the Gulf Coast north into parts of Illinois, Indiana and Ohio, and some could be strong — capable of causing EF2 damage or greater.

The greatest risk of strong tornadoes exists with storms that develop in parts of Arkansas, Missouri, Mississippi and Tennessee in the late afternoon or early evening on Sunday. This is when the potential for supercells is at its peak.

More than 7 million people were under tornado watches by Sunday afternoon across parts of Missouri, Illinois, Arkansas, Oklahoma, Texas and Louisiana, according to the National Weather Service’s Storm Prediction Center. Any tornado on Monday has the possibility to become strong if it can tap into just the right atmospheric conditions.

Damaging thunderstorms will push east overnight and reach the Appalachians and East Coast by Monday morning. Some will likely still be severe at sunrise Monday, but an injection of energy arriving in the afternoon will give the storms a new, even more dangerous life.

A Level 4 of 5 risk of severe thunderstorms is in place Monday from the Carolinas to the Maryland-Pennsylvania border, with a wider Level 3 of 5 risk in place in surrounding areas.

Damaging straight-line wind gusts are again expected to be the thunderstorms’ most widespread impact, with gusts past 75 mph possible in storms from Georgia to Pennsylvania and New Jersey.

Potentially historic snow, blizzard conditions

While the southern, warmer side of the storm is generating severe thunderstorm concerns, the cold northern side has been busy generating a lot of snow.

The powerful storm has already dropped a wide stretch of significant snow from the northern Rockies to the Great Lakes since first forming on Saturday.

More than a foot of snow buried parts of southern Minnesota and central Wisconsin by Sunday morning, with plenty more to come. Snow will continue through Monday for much of the Midwest and Great Lakes.

This storm could be the snowiest ever in cities like Rochester, Minnesota. Parts of the city picked up about a foot of snow by Sunday morning, with up to another foot possible by the time the storm comes to an end. Rochester’s heaviest snow was from a March 2005 storm that dropped 20 inches.

Parts of Michigan’s Upper Peninsula are forecast to end up with snow totals of more than 3 feet by Monday night.

Marquette, Michigan, is no stranger to high snow totals from lake-effect snow, but this storm could be one of its biggest ever. The city’s largest two-day storm total on record stands at about 32 inches from a March 1997 storm. It’s forecast to get anywhere from 2 to 4 feet of snow from the current storm.

And it’s not like this snow is falling in a peaceful winter wonderland — powerful winds are whipping it up to create dangerous whiteouts and longer-lasting blizzard conditions.

The punishing conditions are making travel extremely hazardous and could cause power outages to increase.

Blizzard warnings were in effect for more than 11 million people from the Dakotas and Nebraska to the Great Lakes Sunday morning. These warnings will continue into Monday for most, as the worst conditions slowly start to come to an end.

CNN Meteorologist Brandon Miller contributed to this report.

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