"Hypothermia will be a significant threat for anyone outdoors starting late tonight and continuing through Friday into Friday night," the National Weather Service said.
A dangerously cold blast of arctic air engulfing the region Friday and Saturday will challenge records.
Exposed skin is at risk of frostbite, just one of the medical dangers that come with air this cold, an emergency department doctor said.
Chemical treatments will stop working on icy roads in the wake of the snowstorm forecast to dump as many as 6 inches on the region tonight into Friday, officials said.
"Water pipes may freeze and burst with the very cold temperatures expected at sunrise Saturday," the National Weather Service said in a storm briefing this afternoon.
How cold is it going to get?
The weather service forecasts a low Friday night of minus 3 degrees Fahrenheit at Lehigh Valley International Airport, where the record low for Jan. 3 was 6 above zero in 1945. The record low for Jan. 4 was set in 1981 at minus 4; temperatures are forecast Saturday to rise to 27 before dropping back to the teens at night. Weather service records date to 1922.
"Hypothermia will be a significant threat for anyone outdoors starting late tonight and continuing through Friday into Friday night," the weather service said this afternoon.
Dr. Tony Luizza, an emergency physician at St. Luke’s University Hospital in Fountain Hill, said hypothermia is a risk during prolonged exposure to any temperature below freezing, 32 degrees Fahrenheit. It "can happen a lot quicker" when temperatures approach 0, he said.
Symptoms can mimic those of a stroke, including slurred speech and altered mental status, he said; complications can be as severe as cardiac arrhythmia and potentially cardiac arrest.
"The biggest advice is to try and be smart about it," Luizza said. "If you can avoid being outside, that would be the best thing to do."
If you're going out, be ready
For those who must be outside, even for short periods of time, Luizza recommends wearing several layers of clothing, hats, scarves and gloves to protect as much skin as possible. Come into a warm area as often as possible. To warm up exposed skin, rub hands together or run warm water over them; however, if frostbite is feared, minimize friction to the affected skin, he said.
Anyone driving should keep "essential items in their vehicle such as food, water and warm clothes to help contend with the potential for dangerous conditions if travel delays occur," Dave Holl, deputy director of operations at the Pennsylvania Emergency Management Agency, said in a statement.
"Wind and extreme temperatures could lead to hazardous driving conditions, and dangerous wind chills will make it unsafe to be outside for any extended period of time," he continued.
Getting ahead of the storm
Road crews, ahead of the snow, treated roads with liquid salt brine. The anti-icing solution is sprayed on roads so snow doesn’t easily bond with the surface, said Ron Young, spokesman for the Pennsylvania Department of Transportation.
As it gets colder, road-treatment chemicals lose effectiveness, the weather service said. PennDOT planned to switch from salt to a mixture of fine stone and sand to try to provide traction if roads are not clear, Young said.
Tim Greeley, spokesman for New Jersey Department of Transportation, said this afternoon that officials have been tracking the storm since the beginning of the week. The goal was to lay down brine and salt and get out in front of the storm, he said.
"Once you get that accumulation to a certain level where you're behind and trying to fight to catch up to get roads clear, it becomes increasingly difficult to do so," Greeley said.