Sub-zero temperatures put Northwest Indiana and the Chicago area in a deep freeze Sunday on the first day of winter.

And for those without power from Thursday and Friday's snow and ice storms, Sunday remained a difficult day.

NIPSCO said on a recorded message that as of 4 p.m. Sunday, 20,500 customers were without power. Nearly 10,000 of those residents were in areas in or near Hammond, Gary and Valparaiso.

Spokesman Mike Charbonneau said outages were the result of ice and tree limbs damaging power lines. He said the storms affected more than 100,000 customers. Over the recorded message, Charbonneau urged customers without power to continue having patience and that all available crews and contractors were out working on problems.

According to the National Weather Service in Romeoville, Ill., there's a wind chill advisory in effect until noon Monday. Around 4 p.m., in Gary it was minus 2 degrees and at O'Hare Airport it was minus 3 degrees.

Bill Nelson, a National Weather Service meterologist, said earlier today, the wind made it feel around 50 degrees below zero in Gary and Valparaiso. Relief in the form of temperatures in the mid-30s may arrive mid-week, but cold temperatures will be around in the next few days.

"We're not going to get out of the deep freeze until Tuesday," Nelson said.

Crews working for ComEd restored power for most of the customers who didn't have it earlier this weekend, but more than 10,000 customers remain affected because of high winds. Around 78,000 customers lost power Dec. 19 and 61,000 customers lost power today.

Crown Point officials declared a state of emergency Sunday because of cold weather. Some residents in the city lost power earlier today and rides were offered to warming shelters at the civic center and the Southlake YMCA.

The town of Lowell also opened warming centers at the police and fire departments to help residents deal with conditions. Lansing police said the department building was available as a warming center, although a weather emergency wasn't announced.

Commissioners in Porter County declared a weather emergency this afternoon and opened up warming centers at various locations, according to Phil Griffith, emergency management director for Porter County. They are at fire department stations in Hebron, Lakes of the Four Seasons, Portage and Porter Township's Lake Eliza station on Division Road and Woodland Park in Portage.

Griffith said in talking to NIPSCO, the largest problem the utility is having to deal with outages resulting from high winds in addition to those already caused by storms days ago. The warming shelters aren't meant to house people permanently, but if necessary, the county has cots for people, Griffith said.

"If it [the wind] doesn't die down, then we have to consider having them spend the night," he said.

Depending on the need, more may need to be requested from sources including the American Red Cross or the state, Griffith said.

Barbara Illo said her daughter Nancy lives in Lake Village and she was in her daughter's home when power went out around 3:30 a.m. Friday. Illo said since there aren't many customers in the area that maybe they are being ignored, especially since customers who've been without electricity for shorter times have had power restored.

"We're surving I guess," Illo said. "It's sort of difficult to understand why we're still without power."