The National Weather Service has posted a frost advisory for much of Maryland tonight, with portions of the western counties warned to expect a hard freeze. The frost advisory includes Howard, Montgomery, northern Baltimore County, Harford and much of the northern half of the Eastern Shore. Counties on the western shore, from Baltimore southward, are not included.

Here's the BWI forecast, which predicts a low of 37 degrees tonight. Compare that with Hagerstown.

The freeze warning includes Garrett and Washington, Frederick and Carroll counties.

A frost advisory means that a frost is possible. Sensitive outdoor plants may be killed if left uncovered. A freeze warning means sub-freezing temperatures are imminent or highly likely. These conditions will kill crops and other sensitive vegetation. 

Click here for the details.

This first frost is a few weeks later than the averages for much of the state, but right on time for Baltimore City, if it extended into the city proper, which is NOT in the forecast.