The region is about to experience its coldest three-day stretch since Feb. 5-7, 2007, and it's going to give that one a run for its cold cash.
But the cold, which is a certainty, may be upstaged during the next few days what is shaping up as a monster storm -- at least virtually.
Computer models continue to show the potential for an East Coast blockbuster Tuesday into Wednesday, and if the model runs stay reasonably consistent, watch out for a threat big enough to set off the requisite panic-shopping stampedes.
In an afternoon discussion, Alex Sosnowski at Accu-Weather talked about a mega-storm that could mean "major travel disruptions" and "perhaps life-threatening conditions."
The dynamics appear to be aligning for something nasty. An area of low pressure is forecast to migrate out of the Gulf of Mexico and blow up off the East Coast as it interacts with strong temperature contrasts.
The air in place around here will be so cold that even if the storm were to draw in warmer air off the Atlantic, the precipitation would start as snow.
We will issue the usual consumer caveats: It is only Friday, and our first rule of weather is that what might happen almost always is more interesting than what is happening.
This morning, the longer-range forecasts were calling for snow to break out before daybreak Tuesday; now it looks like Tuesday afternoon.
We're willing to bet that the timing will wiggle around a whole lot more between now and Monday. For now, the official National Weather Service forecast is calling for a 40 percent chance of snow Tuesday, and 50 percent Tuesday night into Wednesday, with a changeover possible.
In the meantime, no panic before its time. If you have a particularly strong heart and want to keep up with the trials and tribulations of the models and the people who follow them, check out the American Weather Forums.
The forecasts do call for a 100 percent chance of frigid temperatures, and it won't get out of the 20s until that aforementioned Tuesday.
Based on the forecast, Philadelphia's official temperatures would average near 17 for the three-day period, hitting bottom at 8 on Monday morning. The nights probably will be a shade colder in areas with a decent snow cover.
The three days would rival the Feb. 5-7, 2007, period, when the average was 17.
For those tired of winter, we will note that this weekend marks an important benchmark. Based on climatological normals, tomorrow, Jan. 22, is the precise midpoint of the heating season.
On average, the Philadelphia heating season lasts 233 days -- from Sept. 28 to May 19, when the cooling season kicks in -- and Jan. 22 would by Day 117. So, all things being "normal" (which would be abnormal), the heating season is half over.
Our thanks to loyal reader and meticulous degree-day counter Peter Brigham, one of the few human beings we've found who truly understands the degree-day concept.
He plans to celebrate the occasion and believes it should be a local holiday. (We won't ask about leap year.)
It does always fall on the same day of the week as Christmas and New Year's.