The first Frost Advisory of the season has been issued for Tuesday morning October 11 north and west of Baltimore. This includes northern Harford, Baltimore, Carroll, and Frederick Counties and all posit west in Maryland. Also southern Pennsylvania that includes Lancaster, York, and Gettysburg.
This mainly poses a threat of damage to sensitive plants, and perhaps some stinkbugs. The general idea is that a clear sky and calm wind will allow temperatures inland to drop into the 30s. Especially in sheltered valley locations. Meanwhile hilltops can stay a little warmer as warm air rises from valley floors.
Compare to the Average First Frost Dates (see map and article here)
Urban areas and places near the Bay will likely stay protected and warmer in the 40s. Here is the projected low temperatures as seen on the NAM Model