Today's the coldest day of the season so far, but it won't be for long.

Next week could see highs under 30 and lows in the teens - conditions seen only a dozen times last winter in Philadelphia.

The temperature fell to 21 degrees at about 5 a.m. at Philadelphia International Airport, quite a bit below the previous seasonal low of 29 set Wednesday, according to the National Weather Service.

Lincoln Drive was closed this morning because of ice formed after a water main break.

At 7 a.m., the temperature was in the teens from Lancaster (17) to Quakertown (14) to Allentown (14), and only 12 at Mount Pocono.

Because of heating problems, classes were canceled today and a Christmas Show postponed at Our Lady of Mount Carmel School in Doylestown.

Next week promises to be even chillier - after a weekend warmup.

Philadelphia's highs are expected to swing upward, from the high 30s Friday to mid-40s Saturday to low 50s Sunday, when periods of possibly heavy rain are expected.

The storm could bring snow, sleet or freezing rain from Central Pennsylvania to New England, according to Accu-Weather.

Monday could bring flurries to Philadelphia, a high in the mid 30s, and an overnight low in the mid-teens.

A high of 27 is forecast for Tuesday, again with a low in the mid-teens.

Temperatures should then moderate, with a high about 40 and a low about 30 on Saturday, Dec. 18, according to the 10-day forecast at weather.com.

No records are threatened. The low marks are single digits for December's last three weeks, except for a 10 on Dec. 14.

Dec. 30 even hit -5 degrees in 1880.

For the latest forecast, go to http://go.philly.com/weather.

Contact staff writer Peter Mucha at 215-854-4342 or pmucha@phillynews.com.