The skies are clear this morning - you should have seen the full moon before sunrise - but boy is it cold outside.
And it's going to stay that way through the weekend.
As of 7 a.m., the wind chill in Philadelphia was a fog-breath-stealing 4 degrees - the result of 18 degrees with a 7 m.p.h. breeze.
The city called a Code Blue last evening, with police and other service workers sweeping people into shelters. To get help for someone out in the cold, call the outreach hotline at 215-232-1984.
Expect more arctic weather for several days, with winds as strong or a little stronger, and highs in the 20s today and tomorrow, and around the freezing mark on Sunday.
Jan. 3, when the high hit 27 in the city, was the only other day this winter to fail to hit the 30 mark.
Lows in the upper teens tonight and tomorrow night will only moderate slightly into the low 20s Sunday, Monday and Tuesday nights.
Highs should become more seasonal, reaching the upper 30s Monday and Tuesday - which could bring some light snow - then trending into the low 40s Wednesday and Thursday.
The cold won't come near the record lows. This date in 1963 saw minus-3 degrees. Tomorrow's mark is 8, set in 1948.
The lowest temperature in Philadelphia so far this winter was 15, reached on Jan. 10. The nights before and after also dropped into the teens, and so did four nights in late December.
Last winter, a half-dozen days hit 15, and three were even colder, reaching 10 on Jan. 16, 6 the following night, and 13 on March 3.
For more on the forecast, go to http://go.philly.com/forecast.