As wildfires raged across the Carolinas on Wednesday, millions of people in the southern U.S. and the Pacific Northwest braced for looming storms that could unleash heavy rain, flooding and possible tornadoes this week.

In Texas, a system moving over the area could bring 5 to 10 inches of rain, prompting flood watches across multiple counties. The storm system is expected to expand eastward over the coming days and could lead to possible flooding in Louisiana and Mississippi.

On the West Coast, powerful storms are forecast to unleash a barrage of dangerous weather conditions beginning Wednesday afternoon, meteorologists said.

"Supercells are expected west of the Cascades across Oregon into Washington," according to the Weather Prediction Center. "These may produce large hail, perhaps a brief tornado, and locally strong gusts."

Meanwhile, extreme fire weather threatened to fuel the blazes that have forced people from their homes in North and South Carolina this week. Across both states, the weather service issued red flag warnings on Wednesday.

Firefighters in the Carolinas continued to battle wildfires Wednesday amid a relentless bout of high winds, low humidity and dry conditions.

In North Carolina, emergency responders attempted to gain control over three wildfires that have consumed 10 square miles of land, triggered rounds of evacuations and destroyed at least 11 homes.

In South Carolina, wildfires in Greenville and Pickens County quickly expanded in size on Tuesday and prompted evacuation orders. The Table Rock and Persimmon Ridge fires have burned 5 miles square of land as of late Tuesday.

"Fire danger will be elevated over the next several days as most of the state is forecast to have low relative humidities and higher-than-normal winds, coupled with drying fuels from a lack of significant rain," the state's forestry commission said in a statement.

The largest and most threatening weather event on the horizon will occur over the weekend and could impact two-thirds of the country.

Forecasters say more than a dozen states from the Gulf Coast to the Great Lakes could see dangerous storm conditions "ranging from damaging wind gusts to large hail and even tornadoes," according to an AccuWeather forecast.

The cross-country storm will break out on Saturday before moving into the East on Sunday, bringing downpours and tornado threats to the Eastern Seaboard, from northern Florida to Maryland. The storm will continue to impact the eastern U.S. into next week, AccuWeather said.

Temperatures could reach record-breaking highs in the Pacific Northwest on Wednesday as the Great Lakes and Northeast regions experience snow and unusually low temperatures.

"High temperatures reaching into the 70s will challenge or break daily records across the Pacific Northwest and into the northern Great Basin this afternoon," the National Weather Service said. "By Thursday afternoon, record warmth will shift east toward the central Plains."

At the same time an upper-level trough in the Northeast is keeping temperatures well below freezing overnight from Michigan and Indiana to Pennsylvania and western New York, resulting in snow flurries.

In the coming days, the heat in the West will steadily move eastward, surging temperatures in the Great Lakes and Mid-Atlantic regions into the high 70s and 80s by the weekend.

This article originally appeared on USA TODAY: Storms, tornadoes threaten much of US; wildfires rage in Carolinas