A lesser risk of wild fire exists for Southeastern Pennsylvania.
The freeze warning is for 3 a.m. to 9 a.m. Tuesday for the entire Philadelphia region, from Harrisburg to Allentown to Atlantic City to southern Delaware.
The concern is that even a single night of frost damage could ruin buds on farmer's fruit trees, which prematurely blossomed during last week's warm-up.
Today started relatively mild, even reaching 50 in Philadelphia by 7 a.m. But because of a cold front coming through this morning, the temperature had only reached 52 by 1 p.m. at Philadelphia International Airport.
High winds made it feel chillier.
As for the freeze warning, the National Weather Service said, "Any vegetation susceptible to freezing temperatures over a period of three or more hours would be at risk."
Some of the forecast lows: 29 in Philadelphia, 26 in Reading, 28 in Atlantic City, 30 in Lancaster.
The cold snap also is a warning that it's too early to put out vulnerable plants. The general rule is to wait until Mother's Day - the second Sunday in May - in this area.
The last three years, however, the city's final spring day with freezing temperatures was in March.
The rest of the week should be closer to normal, with highs in the low 50s Tuesday, mid-60s Wednesday, about 60 Thursday, and mid-50s Friday.
In Philadelphia, lows might dip into the upper 30s only Tuesday and Friday nights. Wednesday's overnight low might be near 50.
The only precipitation this week is a 30 percent chance of showers on Wednesday.
For more on the forecast, go to http://go.philly.com/weather.
Contact staff writer Peter Mucha at 215-854-4342 or firstname.lastname@example.org.