Tornado Watches and Warnings

During spring, summer and fall throughout much of the United States tornado watches are quite common. Knowing exactly what is meant when a tornado watch is issued and what do do when your region is under such a watch is important to you and your family’s safety.

Tornado watches are issued when impending conditions are favorable for the creation of a tornado. The Storm Prediction Center (SPC) of the National Weather Service (NWS) monitors weather conditions continually and issues warnings when any severe weather is likely. The SPC attempts to issue tornado watches as much as two days in advance but changing conditions can result in modifications to watches, or even new watches issued, with just hours or minutes ahead of severe weather.

Meteorologists at the SPC monitor a number of conditions to determine the chance of tornadoes forming. Four factors are required for tornadoes; moisture, instability, lift and wind shear. These factors commonly come together with advancing cold fronts across the center of North America meeting warm, moist air moving north from the Gulf of Mexico. These cold fronts form severe thunderstorms which have the possibility of creating tornadoes but not all thunderstorms will create tornadoes and others conditions can also lead to the formation of tornadoes.

Particularly strong cold fronts meeting with unusually warm and moist air are very likely to form conditions favorable to tornadoes and are likely to cause the SPC to issue a tornado watch. Even absent such conditions, however, the weather situation can change rapidly. Often warnings are issued as cyclonic storms form throughout the heat of the day.

A tornado watch is upgraded to a tornado warning when there is evidence of the formation of a tornado. In the past only a trained spotter actually seeing a tornado would generate such a warning. Today, however, sophisticated Doppler radar can usually detect tornado formation long before an eyewitness observes one. Particular signature patterns of wind activity from such radar will result in a tornado warning being issued.

Since tornadoes are almost always associated with severe thunderstorms a tornado watch also includes a severe thunderstorm watch. Even if a thunderstorm does not produce a tornado it is likely that damaging rain, wind and hail will occur. Every tornado watch should be taken seriously and you should be prepared for severe weather.

When a tornado watch is issued you need not head immediately to shelter. However, it is important when your area is covered by such a watch you stay aware of the weather around you. Keeping your “eyes on the sky” and having access to official sources of weather information, such as radio and television, can be very important to the safety of your family.