SAVANNAH, Ga. -- A brutal winter storm smacked the coastal Southeast with a rare blast of snow and ice Wednesday, hitting parts of Florida, Georgia and South Carolina with their heaviest snowfall in nearly three decades.

Forecasters warned that the same system could soon strengthen into a "bomb cyclone" as it rolls up the East Coast, bringing hurricane-force winds, coastal flooding and up to a foot of snow.

At least 17 deaths were blamed on dangerously cold temperatures that for days have gripped wide swaths of the U.S. from Texas to New England.

Schools in the Southeast called off classes just months after being shut down because of hurricane threats, and police urged drivers to stay off the roads in a region little accustomed to the kind of winter woes common to the Northeast.

In Savannah, dump trucks spread sand on major streets before the storm and police closed several bridges, overpasses and a major causeway because of ice.

The National Weather Service recorded 1.2 inches of snow -- Savanna's first measurable snowfall since February 2010 and the first that exceeded an inch in 28 years.

Across the Georgia-South Carolina line in Charleston, the weather service reported 5 inches as the snow was winding down at 5 p.m.

Airports shut down in Savannah, Charleston and elsewhere as airlines canceled 500 flights Wednesday, and at least 1,700 more were canceled for today. Interstate 95 was nearly an icy parking lot for almost all of its 200 miles in South Carolina. Troopers couldn't keep up with the number of reported wrecks which numbered in the hundreds.

In Tallahassee, Florida, Michigan transplant Laura Donaven built a snowman 6 inches tall. The city tweeted that snow fell there for the first time in 28 years.

The weather service said the winter storm will probably intensify into a "bomb cyclone" that could dump more than 8 inches of snow on the Boston area on Thursday and at least half a foot of snow in the New York City region.

Meteorologists have been using the term "bomb" for storms for decades, but the phrase went viral on social media Wednesday. A storm is a bomb -- or bombogensis happens -- when it drops 24 millibars of pressure in 24 hours. This storm looks like it will intensify twice that rate, said Bob Oravec, lead forecaster at the National Weather Service's Weather Prediction Center.

Mississippi's largest city said record cold is breaking water mains, leaving some customers with little or no water flow.

Jackson city spokeswoman Kai Williams said Wednesday evening that the city knew of 37 separate water main breaks that it attributed to cold. The city has declared an emergency and is hiring outside contractors to help repair water main breaks.