How often do the Orioles open their season under a tornado watch?  Most of Maryland and Virginia (and parts of the Carolinas, Georgia and Pennsylvania) were placed under a tornado watch at 4:15 this afternoon as a cold front approached with a threat of severe thunderstorms. A station near Hancock reported three-quarter-inch hail this afternoon. Here's a radar image showing the storm front.

Here's how the tornado watch reads for counties in the Sterling, Va., forecast area:

THE NATIONAL WEATHER SERVICE HAS ISSUED TORNADO WATCH 148 IN
EFFECT UNTIL MIDNIGHT EDT TONIGHT FOR THE FOLLOWING AREAS

THE DISTRICT OF COLUMBIA

IN MARYLAND THIS WATCH INCLUDES 13 COUNTIES

IN CENTRAL MARYLAND

ANNE ARUNDEL          HOWARD                MONTGOMERY
PRINCE GEORGES

IN NORTH CENTRAL MARYLAND

CARROLL               FREDERICK             WASHINGTON

IN NORTHERN MARYLAND

BALTIMORE             HARFORD

IN SOUTHERN MARYLAND

CALVERT               CHARLES               ST. MARYS

IN WESTERN MARYLAND

ALLEGANY

Here's a definition: 

Tornado Watch (SEL):  This is issued by the National Weather Service when conditions are favorable for the development of tornadoes in and close to the watch area.  Their size can vary depending on the weather situation.  They are usually issued for a duration of 4 to 8 hours.  They normally are issued well in advance of the actual occurrence of severe weather.  During the watch, people should review tornado safety rules and be prepared to move a place of safety if threatening weather approaches.