Severe Thunderstorms

The National Weather Service defines a severe thunderstorm as having large hail, at least 3/4 inches (0.75 inches) in diameter, and/or damaging winds, at least 58 mph, or 50 knots.

Lightning, no matter how frequently it is striking, is not a criterion for determining whether a storm is severe by national weather service definitions.

A severe thunderstorm watch is issued when severe thunderstorms are possible. It generally covers a large area, perhaps several states. A severe thunderstorm warning is issued when a severe thunderstorm is occurring or expected to occur within a matter of minutes.

Pay very close attention to the weather whenever any severe weather threat exists and watches and warnings have been issued because tornadoes can form suddenly.

The following are the hail sizes that the national weather service equates with various terminology:

Pea..............1/4 inch, not severe

Marble...........1/2 inch, not severe

Mothball.........1/2 inch, not severe

Dime.............3/4 inch, severe

Penny............3/4 inch, severe

Nickel...........7/8 inch, severe

Quarter..........1   inch, severe

Half dollar......1 1/4 inches, severe

Walnut...........1 1/2 inches, severe

Ping pong ball.. 1 1/2 inches, severe

Golf ball........1 3/4 inches, severe

Hen egg..........2 inches, severe

Tennis ball......2 1/2 inches, severe

Baseball.........2 3/4 inches, severe

Tea cup..........3 inches, severe

Grapefruit.......4 inches, severe

Softball.........4 1/2 inches, severe

Downburst: a sudden rush of cool air toward the ground that can impact with speeds greater than 70 mph and produce damage similar to that of a tornado. Viewing the damage from the air does not reveal evidence of a twisting motion or convergence toward a central track, like it would for a tornado.