Lows are expected to reach below-freezing temperatures within the pink line.

Lows are expected to reach below-freezing temperatures within the pink line. (Eric the Red / April 27, 2012)

The National Weather Service has issued freeze warnings and watches for several Maryland counties overnight Friday into Saturday, but one local weather watcher is predicting it will be a "hard freeze" in the 20s.

A freeze warning is in effect for Frederick and Carroll counties, with a frost advisory in northern Baltimore, Howard and Harford counties. Temperatures are expected in the lower 30s.

Baltimore professional meteorologist Eric the Red said Thursday early information indicates it will be even colder. The best chances of a freeze tonight are in the northern and western suburbs, "while areas near or inside the Beltway and along and east of I-95 will likely be spared," he wrote in an e-mail.

Freeze risks this late in the year are particularly dangerous because early plant growth is vulnerable to being killed. This year's mild winter and spring heat have exacerbated that problem.

The low temperature could threaten a record of 33 degrees for April 28, set in 1998. If it dips below freezing, it would be the third-latest freeze on record for BWI. The latest freezing temperature on record for springtime at BWI Marshall Airport is May 11, at 32 degrees in 1966. BWI also reached 32 degrees April 30, 1961.

Gardeners and farmers are encouraged to cover plants and crops or bring them indoors if possible.