A holiday wish from 911 officials is that people have no need to dial those three numbers. But if you have to make that call, here's some advice from one county's emergency personnel:

Don't hang up.

Chester County officials issued a news release Wednesday to warn residents that icy roads - a possibility in the holiday weekend's forecast - could wreak havoc with 911 service.

The county wants to prevent a rerun of Dec. 13, a Sunday when plunging temperatures brought a bout of black ice, causing more than 100 accidents and jamming the phone lines, said John Haynes, deputy director of the county 911 center.

The center received 1,629 calls from 8 to 11 a.m. that day, nearly double the daily average of 850, Haynes said. He called it the worst surge he'd seen "without any warning" in almost 20 years.

Haynes said hang-ups exacerbated the problem. Though a person might disconnect, the call stays in the system and must be processed. If a dispatcher cannot contact the person, a police officer is sent to the caller's location - unless a cell phone makes tracking the location impossible, he said.

"We dispatch police to every person we can't reach, for the one-in-a-million situation" where the person is in danger and can't respond, he said.

About 50 officers battled treacherous conditions to track down callers that Sunday, said Haynes.

"People don't get faster treatment if they call back," he said. "The second call goes to the back of the line, the service is delayed, and now there's an extra call" in the system.

Avoiding backlogs is a constant goal, but when Mother Nature is in charge - and in the age of cell phones - calls can come fast and furious.

"One accident can generate 50 calls," said Sean Petty, Montgomery County's deputy director of public safety. "It's really a double-edged sword, because you don't want to discourage people from calling."

Chad Brooks, chief of operations for Delaware County's emergency services, said his county, too, saw a small surge the morning of Dec. 13. He said call overloads typically follow an accident on I-95 or the Blue Route, or a pop-up thunderstorm.

Brooks said he hopes the public understands when a dispatcher takes information and tells a caller, "We already have that." It might sound brusque - but "the operator is just trying to clear the backlog and maintain our resources," Brooks said.

Haynes said a system in development to enable dispatchers to work from home would have helped on Dec. 13, but the technology is not yet secure enough. He said extra workers were not summoned because travel was too dangerous.

In the meantime, Haynes urged 911 callers to stay on the line - "even if it seems like an eternity during the stress of the moment."

One more tip from Haynes: If your power goes out, call Peco Energy first at 1-800-841-4141, instead of 911.

Contact staff writer Kathleen Brady Shea at 610-696-3815 or kbrady@phillynews.com.