The coldest weekend since March was followed this morning by the season's deepest freeze.

At 7 a.m., Pottstown hit an overnight low of 19, with 19.9 reported in Doylestown, Millville and Allentown, according to the National Weather Service.

Dipping into the low 20s were Reading and Mount Holly (21), Northeast Airport and Wilmington (22), and Trenton and Atlantic City (23).

Although Philadelphia International Airport was a bit warmer, its low of 27, reached about 7 a.m., was the chilliest temperature recorded there since the end of March.

The next coldest - 28 - was reached Sunday morning, which followed Saturday morning's 31, which matched the season's low up to then, set on Halloween.

Today's forecast high of 47 would actually top the last two days. Sunday's 42 in Philadelphia was the coolest maximum since March 3, when the high was 36.

The workweek will be a little warmer, with highs in the upper 40s and lows in the low 30s Tuesday and Wednesday. With periods of rain possible Wednesday night into Friday, the high could reach the mid 50s Thursday, followed by a low in the mid 40s - about the normal range for mid-December. Friday could also see the 50s.

Then another subnormal weekend is expected, with near-freezing lows Friday night, a high in the lows 40s Saturday, then a return trip to the upper 20s Saturday night, according to the weather service.

Sunday's high might also be in the low 40s, according to the extended forecast at weather.com.

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

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