No need to rush to the supermarket, but the National Weather Service has issued a "freeze warning" tonight for all of Pennsylvania, except Philadelphia, and a "frost advisory" for South Jersey.

Temperatures could fall into the upper 20s in some places, forecasters said.

Winds will be brisk this evening, blowing from the northwest - or in from left-center field at Citizens Bank Park, where the Phillies are hosting the Chicago Cubs.

They will die down later tonight, and under generally fair skies, heat will be escaping rapidly into space, allowing temperatures to plummet.

"We're looking at ideal radiational conditions," said Joe Miketta, a meteorologist at the Mount Holly office.

Miketta, an erstwhile farmer, advises that it's a good idea to bring sensitive plants inside, and if any were outside, "I'd make sure I'd cover it."

The warning is in effect from 2 to 8 a.m., and the advisory from 4 to 8 a.m.

Philadelphia is not included in either alert because the urban heat-island effect probably will keep temperatures above freezing in the city, Miketta said. City buildings store heat during the day and are slow to give it up at night, and that warms the surrounding areas.

If it seems that April has been cooler than March, that's not that far from reality.

April's temperatures have been a few degrees above normal, but they within 4 degrees of March's, a month usually associated with violent winter storms and occasional cold snaps.

Typically April is 10 degrees warmer than March, as the sun begins flexing its muscles in the Northern Hemisphere.

Last month, of course, was the warmest March on record.

Contact Anthony R. Wood at 610-761-8423 or twood@phillynews.com