The worst winter storm of the season threatens to bring snow, ice and cold from Nova Scotia to Florida, including a foot or more in Boston and a few inches in Manhattan.

Winter storm warnings and advisories stretch from Massachusetts to Florida, the National Weather Service said. It was snowing in Tallahassee, Florida’s capital, early Wednesday, according to Rob Carolan, a meteorologist with Hometown Forecast Services Inc. in Nashua, New Hampshire.

The storm will strengthen as it moves north, dropping as much as 12 inches (30 centimeters) in Boston, and 4 inches in Manhattan, as well as 5 in Brooklyn and Queens on Thursday, the National Weather Service said.

“We are going to get a decent snowfall out of this,” said Carolan, referring to New England. “The bad news is it will ruin tomorrow morning’s commute.”

The weather stands to wreak havoc on markets for longer, as electricity prices have already surged to the highest level in years and natural gas demand hit a record high. Georgia Governor Nathan Deal has declared a state of emergency for 28 counties.

Its focus and track will shift north throughout the day until it brings its worst to Boston and coastal New England Thursday. A blizzard warning stretches from Maine to Cape Cod in Massachusetts, with forecasts for heavy snow and winds gusting to 70 miles (113 kilometers) per hour Thursday.

“The real apex, the peak of the storm, will be Cape Cod to Nova Scotia,” said Gregg Gallina, a forecaster at the U.S. Weather Prediction Center in College Park, Maryland.

Snow Bomb

This storm may end up being worse than your average nor’easter. It could turn into a bomb, short for bombogenesis, a phenomenon that occurs when a system’s central pressure drops steeply — 24 millibars or more — in 24 hours.

If current computer models hold, that’ll start to happen somewhere off Cape Hatteras, North Carolina, and continue as the storm moves north. Hurricane-force wind warnings have been posted off the coast where ships could encounter winds of 80 miles an hour and waves as high as 26 feet on Thursday.

“It is certainly going to be a bomb,” Carolan said. “It could drop 40 to 50 millibars in 36 hours.”

Silver Lining

Environment Canada has issued its own warnings for New Brunswick and Nova Scotia, including Halifax, which handles about 1,500 vessels per year.

There’s a silver lining: The storm will offer some respite from the bone-rattling cold that triggered wind chill advisories and freeze warnings.

But the relief will only be temporary as the Arctic chill is set to make a comeback by the end of the week. Temperatures will rise out of the teens and single digits from Philadelphia to Boston before slipping back again by Friday and Saturday.

“This is only the appetizer — the main meal comes over the weekend,” said Judah Cohen, director of seasonal forecasting for Atmospheric and Environmental Research, a Verisk Analytics Inc. business in Lexington, Massachusetts. “This is about as intense a cold as I can remember.”

Another round of bitterly cold air is forecast to blast across the U.S. by the middle of next week. The chill could linger through Jan. 16.