The National Weather Service again has issued a frost advisory for counties north and east of Pittsburgh.
As temperatures dip into the mid-30s overnight, frost is possible in Armstrong, Butler, Clarion, Forest, Indiana, Jefferson, Lawrence and Mercer counties and ridges in Fayette and Westmoreland counties.
Garrett County, Maryland, and Preston and Tucker counties in West Virginia, also may experience frost.
Valleys in the mountains are particularly vulnerable, and sensitive plants outside may die if they are uncovered, the weather service advises. The region experienced a "killing frost" as late as May 29 in 1894, according to weather service records.
Pittsburgh's low will drop tonight to about 38 degrees, with a sunny Memorial Day peaking at about 75 degrees.
Lexi Belculfine: email@example.com or 412-263-1878. Twitter: @LexiBelc.