US states across the Northeast, Great Lakes, and Ohio Valley are facing weather warnings today as a bomb cyclone reaches peak intensity.

The storm brought blizzard conditions to parts of the Midwest on Sunday, particularly Michigan, where there are currently more than 100,000 power outages due to heavy snow and high winds. As the expanding system tracks northeastward toward Canada, the National Weather Service expects these conditions to move eastward into the Great Lakes, where local snowfall totals could reach 2 feet.

“As this system reaches peak intensity early this morning, blizzard conditions can be expected especially over the central Great Lakes,” the NWS stated Monday. “Meanwhile, a mix of snow sleet and freezing rain will spread quickly through New England before warmer air changes the wintry mix to all rain during the day.”

What is a bomb cyclone?

When the barometric pressure of a storm system in North America falls 24 millibars within 24 hours, it is considered a bomb cyclone. This process, called “bombogenesis,” typically occurs when a cold air mass collides with a warm air mass. That’s exactly what happened this weekend when an Arctic cold front encountered a record warm spell across the central and southern U.S.

The rapid pressure drop creates a strong pressure gradient, causing air to rush toward the storm’s center. This fuels intense winds and precipitation. As such, bomb cyclones are more hazardous than your average winter storm and can deliver hurricane-force winds, blizzard-level snowfall, dangerous wind chills, and coastal flooding.

As of Monday morning, more than 30 million Americans are under winter weather alerts across the upper Midwest and Northeast, and blizzard warnings remain in effect for parts of northern Iowa and Michigan’s Upper Peninsula. Wind advisories stretch from the Ohio Valley into the Northeast, with gusts of up to 55 miles per hour (88 kilometers per hour) expected.

These conditions could snare post-holiday travel plans as ice and blowing snow make roadways treacherous and reduce visibility.

Lingering local impacts

Forecasters expect the cyclone to move quickly into southeastern Canada. By Monday evening, much of the snow across the upper and central Great Lakes should taper off, but lake-effect snow will continue to affect some areas downwind, according to the NWS.

These lake-effect snows should linger through at least Wednesday morning as another storm—an Alberta clipper—spreads light snow across the upper Midwest and Great Lakes on Tuesday. The cyclone will continue to send strong and gusty winds into the entire eastern U.S. as it tracks north, with snow showers possible through Wednesday morning across interior New England.

As we close out the year with some wild winter weather, forecasters urge those in the cyclone’s path to stay alert, refrain from traveling, and prepare for rapidly changing conditions. With most of the season still ahead, similarly powerful systems could return in the months to come.