Harford County is under a tornado watch until 10 p.m.

Harford County residents are under a tornado watch Thursday. The new weather alert replaced part of an earlier severe thunderstorm watch.

How long it lasts: The tornado watch includes Harford County and remains in effect until 10 p.m.

Watch versus warning: A tornado watch means tornadoes are possible, not that one has been spotted.

If a warning follows: A tornado warning means radar or reports show a tornado. Residents should move to a basement or an inside room on the lowest floor, away from windows.

What comes next: The National Weather Service can issue warnings for smaller areas if conditions become more dangerous.