Temperatures throughout the region soon will plummet to record lows, making for dangerous conditions, according to the National Weather Service at Pittsburgh.
"It will not be fit for man or beast,'' said John Darnley, a meteorologist with the office, based in Moon.
The weather service shifted its wind-chill watch to a warning at 3:35 a.m. today. Mr. Darnley said that the watch had indicated a potential for dangerously cold weather; the warning signals that "we're confident it's going to happen."
The warning will be in effect from 1 p.m. Monday to 10 a.m. Wednesday for southwestern Pennsylvania, northern West Virginia, and eastern Ohio - the entire forecast area of the weather service at Pittsburgh.
Also issued was a special weather statement advising that a period of light freezing rain was possible today in sheltered valleys where the temperature remains below freezing. The statement covers Allegheny, Fayette, Greene, Indiana, Washington and Westmoreland counties.
Mr. Darnley said temperatures will fall through the day on Monday, reaching a low of about minus-15 degrees between 5 a.m. and 7 a.m. on Tuesday. Other weather conditions will make it feel like minus-36 degrees, Mr. Darnley said.
The normal daily low temperature for this time of year is about 21 degrees, he said.
The last time the region experienced below-zero temperatures was Jan. 22, 2011. The last time the mercury dropped to minus-10 degrees was Jan. 17, 2009. The all-time record low was hit on Jan. 19, 1994, when temperatures bottomed out at minus-22 degrees.
Mr. Darnley said the region is poised to break record lows for the dates of Jan. 6 and Jan. 7. Current records are minus-5 degrees on Jan. 6, 1942, and minus-5 degrees on Jan. 7, 1884.
The Pennsylvania State Police have issued a news release warning that criminal charges will be filed against pet owners who fail to provide their animals with sufficient shelter, food and water. "If possible, cats and dogs should be brought inside," the news release reads.
Mr. Darnley agreed that the cold poses a danger for animals and people alike. He said frostbite, hypothermia and dehydration could happen within minutes. "If you have to be outdoors, you have to be dressed properly. You shouldn't overexert yourself," he said.
The region will have the balance of today to prepare for Monday with temperatures warming to a high of about 47 degrees. The fall toward subzero will begin in the wee hours of Monday. The overnight forecast calls for rain changing to snow showers before daybreak, with winds gusting to 37 mph. Snow showers will continue through early Monday afternoon with continuing gusty winds. Total snowfall accumulation was forecast at less than 2 inches.
Elsewhere, a winter storm warning was posted for Erie and Crawford counties in northwest Pennsylvania from 6 p.m. today through 9 a.m. Wednesday. Several inches of new snow is forecast for Erie, where more than 75 inches has fallen already, to be accompanied by a drop to subzero temperatures and wind chills.