The National Weather Service has posted a "freeze watch" for Philadelphia's neighboring counties and warns that a freeze also is possible in Jersey's Pine Barrens.
Farther north and west, a freeze "warning" is in effect.
It could be a rough night for flowering plants, but generally the blossoms like a little chill in the air, which is why flower shops are chilly.
Relative to March, April has been on the cool side, even though it is averaging a few degrees above normal.
Based on the forecasts, the month will end up averaging 55.5 at Philadelphia International Airport, which is rather amazingly close to March's 52.2.
That will be one of the tightest March-April spreads on record, at just 3.3 degrees. In the 138-year period of record, the average temperature difference between the two months is 10.5.
Scanning the records, we have to go back quite a ways to find similar circumstances.
In 1946, April was just 2 degrees warmer than March, which was quite mild. The only tighter spreads occurred in 1936, 1.8; 1874, 1.6, and 1898, 1.5.
The March-April 2012 spread would finish No. 4 on that list.
At the other extreme, after a quite cold March that featured a major snowstorm, April 1960 was similar to this one and 24 degrees warmer than the previous month.