Straight-line winds are often responsible for most of the wind damage associated with a thunderstorm.

These winds are often confused with tornadoes because of similar damage and wind speeds. However, the strong gusty winds associated with straight-line winds blow roughly in a straight line unlike the rotating winds of a tornado.

If you were to survey the damage pattern left by straight-line winds you would see debris such as uprooted trees laid out in nearly parallel rows.

Down-Bursts

Down-bursts are one example of damaging straight line winds. A down-burst is a small area of rapidly descending rain and rain cooled air beneath a thunderstorm.

Wind speeds in some of the stronger down-bursts can reach 100 to 150 miles per hour, which is similar to that of a strong tornado. The winds produced from a down-burst often occur in one direction and the worst damage is usually on the forward side of the down-burst.

Derechos

Another type of straight-line winds common to the Midwest are known as derechos. Derechos usually occur in the Midwestern states in the late spring and during the summer.

Derechos are created by the merging of many thunderstorm cells into a cluster or solid line extending for many miles. The width of such a storm can range from 20 to 65 miles and the length can reach 100 miles or more.

In extreme cases these storms can create maximum wind gusts of 150 mph. Not only can a derecho contain incredibly strong straight-line winds, it is also capable of producing small tornadoes.

As a result these types of storms can be extremely dangerous and incredibly damaging.

History

In 2000 there were 16 instances of hurricane-force thunderstorm wind -- wind speeds in excess of 75 mph or greater -- in Wisconsin.

Also in 2000 there were two cases where wind gusts reached or exceeded 100 mph, in juneau and rock counties.

In the past 31 years Wisconsin has experienced dangerous hurricane- force winds on 130 days or about four days per year.

A total of 227 instances were reported during this period of time -- a little more than seven cases per year.

In addition, there have been 19 days on record with wind speeds of 100 mph or more. A total of 39 instances with winds gusts 100 mph or more were noted, or a little more than one case per year.

Category 2 Hurricane

Wind gusts of 100 mph or more are equivalent to those of a category-2 hurricane.

Always keep in mind that major damage to a home, building or any personal property can be caused by a variety of different straight- line wind events. Always take cover when strong thunderstorm winds threaten.

As with any severe weather, stay tuned to NOAA weather radio or your local TV or radio stations for the latest forecast and severe weather warnings.

For additional severe weather information, visit the NWS's Web site.

SOURCE: NWS