While severe thunderstorms produce tornadoes, they more commonly produce damaging winds and large hail. To be categorized as "severe" winds must be in excess of 55 mph and hail must be at least 3/4" in diameter or larger.
Severe thunderstorms usually come in two main varieties (althought there are others) - the supercell and the squall line. A super cell thunderstorm is likely to be isolated and exists in an environment of its own. They have a complex internal structure and rotate. Therefore, it is these thunderstorms that usually produce tornadoes. Tornadoes not withstanding, they also produce strong winds and large hail. The squall line thunderstorm is a solid or broken line of thunderstorms that form ahead of a large scale boundary such as a cold front. Although a squall line thunderstorm can produce a tornado, it is most likely to produce strong straight-line winds, downbursts, and large hail. Winds associated with a squall line can easily exceed 100 mph and give the appearance (and sound) a tornado has struck. Many times people believe a tornado has struck their location only to find it was a microburst or straight-line winds after investigation of the damage pattern.
SEVERE THUNDERSTORM WATCH Like the tornado watch, a severe thunderstorm watch is issued when conditions are favorable for severe thunderstorm formation. Many times a squall line situation is found within a severe thunderstorm watch. Keep in mind, severe thunderstorms can and often do produce tornadoes with little or no warning. TORNADOES CAN OCCUR WITHIN A SEVERE THUNDERSTORM WATCH! Should a severe thunderstorm watch be issued for your area, monitor the weather closely in case a warning is issued. Like the tornado watch, the severe thunderstorm watch is issued by the Storms Prediction Center in Norman, Oklahoma.
SEVERE THUNDERSTORM WARNING A severe thunderstorm warning is issued by local National Weather Service offices. Based on ground reports or by Doppler radar, conditions meeting the severe thunderstorm criteria are either occurring or are about to occur within the warned area. You should take shelter immediately.
1. Stay away from windows.
2. Move towards the interior portion of the home.
3. Bring pets inside.
1. Abandon an untied or unanchored mobile home.
2. Stay away from windows.
3. Move towards the interior portion of the home.
1. Abandon cars for more substantial shelter until the storm has passed.
OUT OF DOORS:
1. Again, seek shelter if possible.
2. Find a low-lying area such as a ditch or raving being cautious of rising water.
3. Do NOT seek shelter beneath trees as damaging winds may cause them to break in addition to a potential lightning strike.