A freeze watch is in effect for Carroll County overnight Monday into Tuesday, something known to happen this late in May only once in more than every 10 years.
Temperatures are expected to drop to the lower 30s there early Tuesday, according to the National Weather Service. That could pose a risk of killing crops or gardens.
Further south and east in Baltimore, Harford and Howard counties, temperatures could reach the mid-30s overnight. Lows in Baltimore are expected in the upper 30s.
According to the University of Maryland Extension, the last spring temperature of 32 degrees or below occurs on or after May 4 in 10 percent of years in Westminster. For Baltimore, spring frosts and freezes last occur much earlier, by April 11 in nine out of 10 years.
The Old Farmer's Almanac suggests gardeners take caution with plants like basil and other herbs, geraniums, and tender vegetables like tomatoes and peppers. They should be harvested, covered or brought indoors before a frost.
A light frost occurs when temperatures drop to 32 degrees or colder, according to the almanac. A hard freeze doesn't occur unless temperatures drop well below freezing for a period of 4 hours or more.Copyright © 2015, The Baltimore Sun