Tornado
Description:
A tornado can be defined as a localized, violently destructive windstorm occurring overland, especially in
the Midwestern United States and characterized by a long, funnel shaped cloud, composed of
condensation and containing debris that extends to the ground and marks the path of greatest
destruction. Tornadoes are generated by severe thunderstorms.
Most tornadoes are not powerful enough to cause widespread damage – most are weak and according
to the National Weather Service, 89 percent have a life span of less than 10 minutes and result in less
than 5 percent of tornado fatalities. These weaker tornadoes typically have wind speeds less than
110mph which will damage a wood frame construction home but may completely destroy a mobile
home or outbuilding.
Of the 10 percent of tornadoes that are considered strong, some may last 20 minutes or more and cover
distances in excess of 20 miles. These major tornadoes can have speeds to 165mph, account for 30
percent of tornado deaths and will cause considerable damage to almost any type of structure.
The remaining 1 percent of tornadoes are considered violent in nature and result in 70 percent of
tornado fatalities. They simply destroy everything in their paths, can last more than an hour and travel
more than 50 miles. The only chance for survival in a violent tornado is inside a safe roof or
underground shelter.
Most tornados in the United States occur in the central plains, with the greatest likelihood of twisters in
the southern plains around Kansas, Texas and Oklahoma. Colorado lies of the western fringe of
"Tornado Alley", but our state still averages between 40 and 60 tornadoes per year. The peak season
for tornadoes is in the spring and early summer with June the most active month. This is due to the fact
that the weather patterns that are needed for tornado development are most common in the spring and
early summer.
Tornados can occur any time of the day, but the majority of tornados occur in the afternoon or evening
and usually move southwest to northeast. While they occur statewide, the largest number develops in
eastern Colorado.
History:
Compared with other States, Colorado ranks number 9 for frequency of tornados (The Disaster Center).
The high altitude and drier air make it harder for the monster supercells that spawn the biggest
tornados to form. Most of our tornados are small and short lived. Since 1950, the three counties with
the most tornados have been Weld County, Adam County and Washington County.
•
June 15, 1988: a tornado outbreak occurred in metro Denver with 5 tornados resulting in 7
injuries and damage of excess of $15 million.
•
June 7, 2008: F1 tornado struck Aurora, Southlands Mall with one significant injury and causing
$3,000 in damages. Caused a power outage for 1 ½ hours. While not in Denver County, this is a
neighboring county.
The peak season is mid May through mid August, with June the most active month. However, there is no
hard and fast rule for when tornadoes strike, as Colorado witnessed on March 29, 2007 when Holly,
Colorado was struck by an EF-3 tornado with winds of 165 mph. Two women lost their lives as a result of
that event and 160 homes were damaged.
Preparedness:
Listen to NOAA Weather Radio or to commercial radio or television newscasts for the latest information.
In any emergency, always listen to the instructions given by local emergency management officials.
Be alert to changing weather conditions. Look for approaching storms.
Look for the following danger signs:
•
Dark, often greenish sky
•
Large hail
•
A large, dark, low-lying cloud (particularly if rotating)
•
Loud roar, similar to a freight train.
•
If you see approaching storms or any of the danger signs, be prepared to take shelter
immediately.
Check out Ready.gov/tornadoes for more tips on what to do before, during, and after a tornado.
Learn more:
American Red Cross Tornado Safety
FEMA – Protect Your Property from High Winds
NOAA All Hazards Weather Radio
Sources:
The Disaster Center
The Tornado Project
National Climatic Data Center (NCDC)
National Weather Service