Darrell Sapp, Post-Gazette Fresh snow clings to the sides of the trees along Liberty Avenue in Gateway Center yesterday afternoon. Click photo for larger image.
	More on the story In 100 years, it may be balmy here in February thanks to global warming Weather Page Forecasts, radar imagery and satellite photos
	Steve Mellon, Post-Gazette About two dozen brave souls jumped into the chilly Monongahela River at the S. 18th Street boat ramp as part of the Pitts-Burrrrrgh Drowned Hogs' fund-raiser for Circle C Youth and Family Services yesterday. Click to a video report about their frigid frolic. Click photo for larger image.
	Mark Wilson, Getty Images Rosemarie Drummond and Jerry Grguich were some of the more than 15,000 revelers who jammed Gobbler's Knob yesterday morning to see Punxsutawney Phil forecast and early spring. Click photo for larger image.

The temperature in our region rarely drops below zero. It's happened only four times in the past seven years.

But weather forecasters are warning that Western Pennsylvania could see subzero temperatures in each of the next three days, a cold spell that would be the worst of this young century.

"The coldest air of the season is coming down, and it will be the coldest air of the winter," said Ken Reeves, a senior meteorologist with AccuWeather.

"While we've been enjoying relatively mild weather the last half of December and through January, this cold air mass has been building across the northern part of the globe," he said. "Now the jet stream is bringing this down across the eastern two-thirds of the states. The core of the cold is directed toward the Great Lakes and the Northeast.

"It's going to be in the teens [today]. And [tomorrow], Monday and maybe Tuesday, temperatures may not even get out of the single digits. We probably haven't seen this type of cold weather in quite some time. "

The coldest temperature in our region since 2000 was 4 below zero, Mr. Reeves said.

Russell DeMaris, a meteorologist with the National Weather Service in Moon, said two fast-moving cold fronts, called arctic clipper storms, were headed for our region last night, one after the other. "The normal low for this time of year is 20 degrees," he said. "We're going to be well below that. In some cases, it's possible [tomorrow] and Monday, we might be seeing minus-12-degree wind chills."

The Allegheny County Health Department yesterday urged residents who must go outside to take precautions against frostbite and hypothermia.

Dress warmly in layers and cover as much skin as possible, said spokesman Guillermo Cole. Drink warm, sweet beverages, broth or soup to maintain body temperature. Avoid alcohol and caffeinated beverages because they cause the body to lose heat more rapidly.

If there is any good weather news, Mr. DeMaris said, it will be that it won't be very windy and it will be too cold to snow.

"When the temperature's this cold, you just don't get enough moisture to get a heavy snowfall," he said. "It's a light, fluffy snow, if anything."

With that in mind, Pittsburgh Public Works Director Guy Costa yesterday said he'd ordered his crews to put most of their equipment into garages for the weekend -- a precaution he hasn't taken for a couple of winters.

"If we do get precipitation," he said, "we will have crews out there with a salt-cinder-liquid calcium mix, because rock salt is ineffective when it's 17 degrees or less. Cinders give you traction, and the liquid-calcium chloride will de-ice up to 24 below zero.

"And we'll have crews out 24 hours checking for ice."

Mr. Costa said he'd also directed that taps in garages be left partially open to keep water flowing and avoid pipes icing up and bursting, a recommendation that members of the plumbing industry yesterday urged local homeowners to follow.

Other tips would be to shut off valves leading to outside faucets and to open kitchen and bathroom cabinets to allow heat in the room to circulate around uninsulated pipes.

Joe DeLauder, general manager for Roto-Rooter in the Allegheny County region, said he has put on extra staff for the next few days in anticipation of an increase in calls about frozen pipes. It's a problem he hasn't had to deal with much in the past couple years.

Jill Berardi, spokeswoman for the American Red Cross, Downtown, said the organization's director of emergency services yesterday sent out an e-mail to volunteers about this weekend's forecast, placing them on alert.

"If there is a house fire, and there usually is at least one a day in our area, it becomes a heightened sense of emergency because of the cold weather," she said.

As far as the forecast beyond Tuesday is concerned, Mr. Reeves said the temperatures should climb back up, but they'll still be below normal for this time of year. And there will probably be some serious snow.

"The real noteworthy part of the first 10 days of February is going to be the intense cold. The second 10 days may be known for its storms and snowiness," he said. "It looks like an interesting pattern."

Still, Mr. Reeves and Mr. DeMaris both said it's likely that after that, things will warm up. The same conclusion that could be drawn by those who embrace yesterday's news out of Punxsutawney, where the groundhog failed to see its shadow for the first time since 1999.

"Punxsutawney Phil may say that winter is ending early, but it's certainly not ending next week," Mr. Reeves said.