In Anne Arundel County, senior centers have been declared open to residents of any age who need a place to warm up during the centers' regular business hours, said spokeswoman Karla Schaffer. The centers also offer hot lunches. Representatives of the county's senior care program also are telephoning vulnerable residents to make sure they're all right, Schaffer said.

Harford County officials are advising the homeless and others seeking warmth to visit public libraries and malls.

Area hospitals have seen a smattering of cold-related cases in their emergency rooms the past couple of days. Most weren't that serious, with slurred speech and other symptoms of hypothermia, which can affect one's ability to think or move.

Union Memorial admitted one man, with a core body temperature of 89 degrees Fahrenheit, well below the normal 98.6 degrees. The man, whose name was not released, was in serious condition Wednesday in the intensive care unit, according to Debra Schindler, spokeswoman for MedStar Health, which operates Union and three other area hospitals.

Those seeking to warm their homes can also put themselves into dangerous situations, said a Baltimore Fire Department spokesman, Chief Kevin Cartwright.

"The colder it gets outside, people turn their thermostats up, and some people who are economically challenged — or not — use space heaters to keep themselves comfortable in their homes," he said. "And some of these people use space heaters very close to easily combustible materials."

Cartwright warned that materials such as bedspreads or curtains can ignite from heat even if the heater placed near them doesn't have an open flame. Appliances that emit carbon monoxide should never be used in the home, he added. Kerosene heaters are illegal in Baltimore and can be confiscated.

Temperatures are forecast to meet or rise above freezing Saturday or Sunday, but are still expected to top out in the lower 30s until Monday, when forecasters expect a high around 40, according to the weather service.

Baltimore Sun reporters Carrie Wells, Timothy B. Wheeler and Kevin Rector contributed to this article.