A tornado is the most concentrated form of violent weather, capable of generating winds in excess of 300 mph in the funnel wall, and of moving across the ground as fast as 70+ mph. Such extremes are rare, but do occur. The average tornado has funnel wall wind speeds of 150-175 mph, cuts a damage path about 150 yards wide and moves across the ground at about 30-35 mph. The US has more tornadoes than any other country, and Nebraska consistently ranks about 5th in the US in the number of tornados per year (average - 35 per year since 1950; most in any year to date - 88 in 1990). Terrain has no effect on tornado movement or duration on the ground. The funnel is the "tip of the iceberg"; where and how the tornado moves is determined by what's going on in the ten-mile-high storm cell and the entire storm system.
"Averages" are problems:
Most tornados come out of the southwest and move toward the northeast. Most occur in Nebraska between early April and mid August, with peak activity in May and June. Most develop in the late afternoons and evening. But...tornadoes can and do occur at any time of the year, any time of the day or night, and move in any direction. Seven our of eight funnels that start down out of the clouds pull back up without making contact with the ground. But there have been cases of two or more funnels on the ground at the same time from the same storm cell.
Tornadoes almost always develop in the trailing edge of the storm cell, dropping out of a formation called a wall cloud. A wall cloud is an isolated lowering of the cloud base, a "bubble" from one to three miles in diameter. If you can see rotation in and around a wall cloud, the situation is getting very dangerous.
Wall clouds will sometimes emit a narrow, near-vertical shaft of high-velocity wind called a downburst. Downburst wind speeds can exceed 100 mph. When this wind shaft hits the earth, it turns and moves along the surface, initially at speeds up to 85 mph, and doing as much tree and building damage as a small tornado.
Even the latest Doppler radars do not pick up all tornadoes, nor can they indicate whether a funnel is on the ground. The only way to know a tornado is on or near the ground and therefore a threat to lives and property is for someone to see it and report it. Trained weather spotters are essential in any effective severe weather warning system.
Tornado Watch - A storm with the potential of producing tornadoes is expected to move through the area. In other words, there is potential danger; watch out and prepare.
Tornado Warning - A tornado has been spotted on or near the ground. Take shelter!
A continuous, steady tone from warning sirens for at least three minutes plus broadcast warning by TV stations, radio and Cablevision. NOTE: There is no all clear signal on the sirens; the "all clear" will be broadcast by TV and radio stations.
Three Basic Rules for Finding Tornado Shelter in a Building:
- Get as far away as possible from all outside walls and windows. Move to the central portion of the building (interior rooms or hallways).
- Move to the lowest possible level in the building; below ground is preferable. In a multi-story building, be sure to clear the top floor entirely (the roof may go).
- Make a small target of yourself and protect your head.
Do's & Don'ts:
- DO...Plan ahead during a Tornado Watch so you'll know what to do and where to go for shelter if a Tornado Warning is issued.
- DO...Listen to radio or TV stations during a Watch for up-to-date information on the approaching storm.
- DO...Take a battery-powered radio and flashlight with you to the shelter so you can know when it's all clear and have light if the power fails.
- DO...Use an interior bathroom for shelter in a basementless house, if one is available. If not, an interior room or hall is best.
- DO...Use chair cushions, pillows, folded blankets, folded coats, hard hats, football or motorcycle helmets to protect your head. Over 90% of all serious tornado injuries are head injuries inflicted by flying debris.
- DON'T...Open windows or doors; it doesn't help and can make things worse.
- DON'T...Automatically go to the southwest corner of a basement.
- DON'T...Try to drive away from an approaching tornado; seek shelter in a nearby building, a ditch or under a bridge.
- DON'T...Go outside when a Warning is issued; take shelter immediately!
For additional information, call the National Weather Service at (402) 475-6100