A rash of thunderstorms and tornadoes. The threat of snow and ice. Even unusually warm temperatures in some places.
Much of the United States was bracing for a weekend of extreme or unusual weather on Friday, as a vast storm threatened to unleash everything from treacherous thunderstorms in the Southeast to icy danger in the Midwest. With forecasters predicting that the most severe weather would ramp up with thunderstorms and tornadoes on Friday afternoon and evening, about 40 million people from Texas to Tennessee were believed to be at risk.
“This is a widespread, very intense storm system with virtually all of the weather hazards,” said Bill Bunting, the chief of forecast operations for the Storm Prediction Center in Norman, Okla.
“There are a few days each year where we really are worried about the potential of impact, and this is one of those types of storms,” he added. “All the ingredients are in place today.”
The thunderstorms — which could come with tornadoes, hail and dangerous winds — were predicted to rip through south-central and southeastern states on Friday, with the greatest risks in northeast Texas, northern Louisiana and southern Arkansas on Friday night. Mr. Bunting also warned of the potential for nighttime tornadoes, which can be especially dangerous if people are asleep and not paying attention to weather warnings.
“It’s really important that people respond to warnings and not wait until they have a visual,” he said. “By the time you sense danger, it will be on you.”
Rain, snow and ice were in the forecast for parts of the central and eastern United States, with threats of flooding looming from Arkansas to Ohio.
In Kansas, officials warned of “blizzard-like conditions.” In Fort Wayne, Ind., city officials instructed residents to take home bags of sand to protect their belongings from flooding. In Texas, emergency management officials put boats, helicopters and rescue teams on standby.
Forecasters also warned of potentially icy conditions in a variety of places, mainly in Michigan and parts of upstate New York and New England over the weekend.
A separate storm system also threatened snow in the Northwest, where parts of Idaho and Montana were under avalanche warnings on Friday.
“Geographically speaking, I’d say about half of the lower 48 states are under some sort of weather alert,” said Alex Lamers, a meteorologist with Weather Prediction Center, in College Park, Md.
Meanwhile, much of the East Coast is expected to have unusually warm weather this weekend, with temperatures of up to 30 degrees above average. In Boston, the high temperature could hit the 60s on Sunday.
Mitch Smith and Manny Fernandez contributed reporting.
