Parts of the U.S. are expected to see severe weather Sunday and in the coming days. Over 100 million Americans can be affected by a bomb cyclone, tornadoes, heavy storms and snow.

Thunderstorms may hit the Midwest by 5 p.m. local time on Sunday, with multiple tornadoes, according to the National Weather Service.

More than 50 million Americans in the Mid-Atlantic and Northeast may be impacted by severe weather moving into Monday from the middle of the country. The regions can see isolated tornadoes and hail.

"From the Great Lakes into New England, a grey, chilly, wet and nasty Monday is in store," according to a report from Accuweather.

The West Coast faces severe weather, as well. As of early Sunday, the National Weather Service has been tracking thunderstorms moving northeast along Washington state's coastal waters.

A bomb cyclone along the West Coast will mean strong storms. Parts of California and Nevada could see as much as 10 inches of rain. Seven million people face flash-flood alerts and potential mudslides.

Winds reaching up to 100 mph could hit California's Sierra Nevada mountains causing power outages and falling trees.

A winter storm warning was put into effect from 5 p.m. PT on Sunday to 11 p.m. PT on Monday for portions of the Sierra Nevada from Yosemite National Park to Sequoia National Forest. Heavy snow is expected above 8,000 feet, according to the National Weather Service.

“A stormy and wet period is ahead for large areas of the country over the next 5 days as multiple atmospheric rivers impact the West Coast, and portions of the central and eastern U.S. prepare for developing areas of low pressure and resulting swaths of heavy rain,” the National Weather Service tweeted.

The rain can mean more damage for parts of northern California after a long period of wildfires.

"When we get moderate to heavy rain over these recent burn scars, they can create ash or debris flows," Anna Wanless, a meteorologist for the weather service office in Sacramento, told CNN.

"What that means is mud, ash, and other debris such as trees, boulders and rocks can get picked up in a fast-moving flow (of water), and that can be really dangerous if people are caught in that."