Learning about Severe Thunderstorms
It is important to know the difference between Severe Thunderstorm Watches and Warnings. Watches are issued by the National Oceanic and Atmospheric Administration's Storm Prediction Center, and warnings are issued by regional offices of the National Weather Service. For Austin and the surrounding area the NWS of Austin / San Antonio will issue alerts when severe weather is imminent.
What is a Severe Thunderstorm Warning?
A severe thunderstorm warning, means that a severe thunderstorm is occurring or is imminent based on doppler radar information. You should move indoors to a place of safety. Schools should think about delaying departure of buses, and should take quick action to delay outdoor sports activities, etc.
What is a Severe Thunderstorm Watch?
A severe thunderstorm watch means that the potential exists for the development of thunderstorms which may produce large hail or damaging winds. When a watch is issued, you should go about your normal activities, but keep an eye to the sky and an ear to the National Weather Service's weather radio or local radio and television stations for further updates and possible warnings.
The term severe refers to hail that is dime size, 0.75 inches in diameter or larger, and/or wind gusts to 58 mph or more. Although lightning can be deadly it is not a criterion for what the National Weather Service defines as severe since any ordinary thunderstorm can produce a lot of lightning. Also, excessive rainfall may lead to flash flooding, but heavy rain is not a criterion for the term severe. Severe strictly refers to hail at least 3/4 of an inch in diameter or wind gusts of at least 58 mph.
If hail golfball size or larger is falling, it indicates that a storm is very well organized and likely has a rotating updraft. Any storm producing giant hail should be watched closely for signs of a possible tornado.
A tornado watch, like a severe thunderstorm watch, means that conditions are favorable for severe thunderstorms to form, but it also means that a few storms may be capable of producing a tornado. A tornado warning is the ultimate in severe warnings, it means that a tornado is either occurring or imminent based on radar. You should take cover immediately. Read more about tornado warnings here.