Freezing rain will create hazardous driving conditions Wednesday morning as the second major winter storm in two weeks hits the Southeast.
Residents of Berkeley and Dorchester counties are being advised to stay home.
"Do not attempt to drive or walk," the National Weather Service advises.
The Weather Service urges Charleston County motorists to consider delaying travel until freezing rain ends and road conditions improve by late morning. The risk of ice is higher on bridges and overpasses.
"If you must drive, allow extra time to reach your destination, anticipate icy roads, slow your driving speed and avoid sudden braking and acceleration," the Weather Service said in an advisory issued late Tuesday afternoon.
The state Department of Transportation is monitoring the Arthur Ravenel Jr. Bridge and other spans for ice formation on travel lanes.
The Ravenel Bridge was closed for two days during the last storm. The Don Holt Bridge and Isle of Palms connector were shut for shorter periods.
The ice storm warning for Berkeley and Dorchester counties and the freezing rain advisory for Charleston County are in effect until 10 a.m. Thursday, the Weather Service said.
Because of ice, schools are closed Wednesday in Charleston, Berkeley and Dorchester counties.
All proceedings in state, county and municipal courts are canceled Wednesday because of the winter storm, officials said.
The Ralph H. Johnson VA Medical Center's Goose Creek Primary Care clinic will delay opening until 10 a.m. Wednesday. Other Veterans Affairs clinics will open as scheduled.
Berkeley County employees plan to help the DOT with sanding and salting roads, said Supervisor Dan Davis.
"The biggest danger is to power lines, and people without electricity," he said.
The Dorchester County Emergency Preparedness Department is gearing up for whatever response might be needed, said Director Mario Formisano.
"The big concern right now is road conditions," he said.
South Carolina Electric & Gas is closely monitoring the weather forecast and the direction of the ice storm. Some 300 additional contractors from Indiana, Michigan, Ohio and Kentucky were joining 1,500 workers for the utility, said spokeswoman Kim Asbill.
The biggest problem was anticipated to be downed power lines caused by ice-coated trees and branches falling, Asbill said.
She cautioned people to stay away from fallen lines.
Santee Cooper is preparing for potential significant icing in its service area west of and along the Interstate 95 corridor. Crews tested equipment, stocked materials and fueled vehicles to be ready for outage repair, if necessary, said spokeswoman Mollie Gore.
Berkeley Electric Cooperative said crews are on standby and prepared to work around the clock until service is restored. The workers also will be available to assist other in-state cooperatives as needed.
The town of Mount Pleasant will closely watch for ice formation on roads, said Administrator Eric DeMoura.
Police, fire and public works crews will be ready to respond if necessary, he said.
The city of Charleston will monitor road conditions starting at 5 a.m.
Public service crews are on standby with salt to melt ice on roads.
A handful of evening flights and at least two morning flights arriving and departing at Charleston International Airport were canceled Tuesday because of winter weather conditions in Charlotte and Atlanta, two big connection points for Charleston travelers. The cancellations involved some of the flights offered by US Airways and Delta Air Lines.
States of emergency
Sleet and snow already were falling in parts of South Carolina on Tuesday.
National forecasters predicted up to 1 inch of ice was possible in the Midlands, an amount that could have devastating effects on power lines and trees.
South Carolina hasn't seen a major ice storm since December 2005, when similar amounts of ice fell across the Upstate. At the time, Duke Energy estimated that 60 percent of its South Carolina customers lost power.
Gov. Nikki Haley, after discussing the situation with emergency management officials, declared a state of emergency effective at noon Tuesday. The declaration triggers the National Guard to active duty - to support state agencies with its wrecker teams and four-wheel drive vehicles - and also activates the state's Emergency Operations Plan, through which all state agencies collaborate if assistance is requested by county emergency managers.
The order also puts into effect anti-price-gouging laws and allows the governor to take whatever other steps are needed to protect residents. A second executive order signed Tuesday waives limitations for trucks transporting emergency materials, equipment and supplies.
The governors of Alabama and Georgia declared states of emergency in preparation of the storm. The poor travel conditions for the South will intensify into Wednesday before the storm starts to push up to the Northeast.
Forecasters in Georgia warned Tuesday of a potentially "catastrophic" second blow in a thick layer of ice that threatens to bring hundreds of thousands of power outages and leave people in their cold, dark homes for days.
The streets and highways in metro Atlanta were largely deserted Tuesday as people in the South's business hub heeded advice from officials to hunker down at home, especially after the snow jam two weeks ago saw thousands of people stranded on icy, gridlocked roads for hours when 2 inches of snow fell.
The forecast in Atlanta drew comparisons to an ice storm that in 2000 that left more than 500,000 homes and businesses without power and an epic storm in 1973 that caused an estimated 200,000 outages for several days. In 2000, damage estimates topped $35 million.
Eli Jacks, a meteorologist with National Weather Service, said forecasters use words like "catastrophic" sparingly.
"Sometimes we want to tell them, 'Hey, listen, this warning is different. This is really extremely dangerous and it doesn't happen very often,' " Jacks said.
Hundreds of Georgia National Guard troops are on standby in case evacuations are needed at hospitals or nursing homes, and more than 70 shelters are set to open. President Barack Obama declared a state of emergency in Georgia, ordering federal agencies to help the state and local response during the storm.
Warren Wise, Robert Behre and The Associated Press contributed to this report.