As the tornado moves across the countryside, its general path coincides with
that of the mother cloud, but the point of contact with the surface can be diffi-
cult or impossible to predict with absolute accuracy. Some tornadoes loop
around after striking a particular point on the surface, and then hit that same
point again. The funnel cloud may swing back and forth like the trunk of an ele-
phant, or drill along in a straight line. After a period of a few minutes, most tor-
nadoes begin to dissipate, although some last an hour or more. Depending on the
population density of the stricken area, the damage can range from inconse-
quential to catastrophic.
TORNADO WATCH
Tornadoes are most common in the spring. A warm, muggy day in October is far
less likely to bring a tornado in the northern hemisphere than a warm, muggy
day in May. In the extreme southern United States, most tornadoes take place in
March and April. In the middle of the country, April and May are the most com-
mon months. In the northern plains, May and June bring most of the tornadoes.
Tornadoes are rare west of the Rocky Mountains. They are also unusual in
New England. The Plains states are most subject to tornadoes, but tornadoes can
strike anywhere in the 48 continental states. They have even been seen in Alaska
and Hawaii.
Assuming that you live in a tornado-susceptible region, and it is a spring or
early summer day, you should be familiar with the type of weather that is asso-
ciated with tornadoes. Some signs are a falling barometer, a southerly or south-
easterly wind, and humid air, all occurring together. Tornadoes always take place
in conjunction with thunderstorms, especially large or severe ones.
If you suspect that conditions are right for tornadoes, listen to the weather
forecasts on local radio stations, or check a weather information Web site such
as The Weather Channel (www.weather.com). Officials will issue a tornado
watch for a specific geographic region if it appears that tornadoes are likely to
form in that region. Tornado watches are often issued in conjunction with severe
thunderstorm watches. A typical tornado watch reads or sounds like this: “The
possibility of tornadoes exists until 6:00
P.M. along, and 100 km (60 mi) either
side of, a line from 50 km (30 mi) southwest of Omaha, Nebraska, to 16 km
(10 mi) north of Sioux Falls, South Dakota.” Specific counties and towns are
usually mentioned, because not everyone has a map and pencil handy. When the
watch period expires, a new watch might be issued for a different area, the watch
period might be extended, or the watch might be cancelled altogether.
The announcement of a tornado watch does not mean that a tornado has
been sighted. Many, if not most, of the locations in a tornado watch area will not
CHAPTER 5 Tornadoes
135