Expect a wild swing - for the better - in the region's weather over the next five days.

Tonight, temperatures could fall into the 30s in the Philadelphia area - and even reach or dip below freezing in the Poconos and far northwest New Jersey, according to the National Weather Service.

Frost could even be a threat tonight and perhaps tomorrow night in Bucks County and the Pinelands, said meteorologist Patrick O'Hara.

Then each day will get warmer. By May's arrival Saturday, overnight lows could stay in the 60s and highs could reach the low 80s - staying in that range at least through Monday.

That stubborn grass seed ought to finally sprout.

It might even be safe to plant tomatoes or other tender garden plants this weekend in the city and its suburbs.

On average, the last frost is around May 5 for Philadelphia and its suburbs, with May 15 a safe date in 9 out of 10 years, according to Scott Guiser, an educator with the Penn State Extension Service in Bucks County.

Indeed, the last time any May day fell below freezing in the city itself was May 11, 1966, when 28 degrees was reached - and that's the city's only May date with a record low at or below freezing.

The 10-day forecast supports such optimism, with no lows below 50 from Friday to May 6, according to weather.com.

The coming pattern of warmer weather is likely to last, O'Hara agreed.

"Nothing for this weekend through the following week looks below normal," he said.

The city's normal range for late April and early May is lows around 50, highs in the upper 60s.

Although some thunderstorms are possible as the threat of rain returns Saturday night to Monday, they shouldn't be too violent, O'Hara said.

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.