What causes a tornado, and how do they form?

suprcell diagram

According to the Glossary of Meteorology (AMS 2000), a tornado is “a violently rotating column of air, pendant from a cumuliform cloud or underneath a cumuliform cloud, and often (but not always) visible as a funnel cloud.”  According to the Storm Prediction Center, in order for a vortex to be classified as a tornado, it must be in contact with the ground and the cloud base. A large variety of weather patterns can lead to tornadoes, but they most often occur in super cells – which are rotating thunderstorms with a well-defined radar circulation called a mesocyclone. A strong updraft of air into the storm may begin to rotate as the wind changes direction higher in the atmosphere, which can produce a rapidly rotating column of air that eventually makes contact with the ground – a tornado.  However, not all super cells will produce a tornado.

It’s this uncertainty and the tornado’s ability to form rapidly that make a weather radio essential in any home.

What are the different types of tornadoes?

Tornado observers, storm trackers and storm chasers usually classify a twister based on its appearance. Tornadoes may not always have the classic “funnel” appearance – wider at the cloud base and narrower at the surface.

“Wedge” tornadoes appear to be at least as wide as they are tall.  “Rope” tornadoes are very narrow and often snake-like.  “Stovepipe” tornadoes resemble cylinders and can sometimes also fit into the definition of a wedge tornado.  While wedge tornadoes are generally regarded as the most intense, any tornado can be destructive, regardless of shape or size.

How many tornadoes are there each year?

2011 tornado map

According to the Storm Prediction Center, recent trends indicate around 1,300 per year, give or take a few hundred. The actual average is unknown, because tornado spotting and reporting methods have changed so much in the last several decades that the officially recorded tornado climatologies are considered incomplete.

Also, in the course of recording thousands of tornadoes, errors are bound to occur. Events can be missed or misclassified; and some non-damaging tornadoes in remote areas could still be unreported.

What is the difference between a tornado watch and a warning?

A watch means severe weather is possible during the next few hours, while a warning means that severe weather has been observed, or is expected soon. A tornado watch is issued when conditions are favorable for the development of tornadoes. Warnings may be issued based on Doppler radar-indicated rotation within a thunderstorm, suggesting tornado formation, or based on eyewitness reports of a tornado on the ground.

High winds, hail, heavy rain and lightning can knock out power. When you can’t turn on the television or your regular radio, a weather radio (either emergency crank or battery powered) is the only way you’ll be able to receive severe weather alerts and tornado warnings.

How can I be prepared for severe weather and tornado season?

Stay up-to-date on the latest severe weather forecast, especially if it is calling for thunderstorms, by watching local TV channels or listening to your NOAA Weather Radio (like the Midland WR120.)

Stay close to home or know where you can take shelter if you will be away. Carry a portable NOAA Weather Radio (like the Midland HH54VP) with you for instant weather alerts while outdoors or on the road.

For more tips on tornado preparedness and seeking shelter, visit the SPC Tornado Safety page: http://www.spc.noaa.gov/faq/tornado/safety.html

For advice on what to do before, during and after a tornado, check out the Red Cross’s Tornado Safety Checklist: http://www.redcross.org/www-files/Documents/pdf/Preparedness/checklists/Tornado.pdf

Why is the NOAA icon flashing on my WR120?

The flashing NOAA icon can indicate that the radio is not receiving a strong signal from the National Weather Service. If the radio is receiving a clear broadcast from the NWS, and is programmed with the correct county code, and corresponding NOAA channel, the flashing icon should have no affect on the radio receiving the NOAA alerts.

To check the radio, press the “Weather/Snooze” button to ensure that the radio is receiving a clear broadcast from the National Weather Service. If you can hear static while listening to the NWS broadcast, we suggest moving the radio near a window with the antenna fully extended, in order to receive the strongest signal possible.

Where can I find more tornado information?

Visit the Storm Prediction Center’s FAQ about tornadoes: http://www.spc.noaa.gov/faq/tornado/
Current weather resources for tornado watches, warnings and severe weather:

If only you’d had more time… If only you’d heard the tornado warning… If only you’d had a Midland weather radio

With up to 300 mph winds, tornadoes are violent storms that stem from powerful thunderstorms. Tornadoes are capable of wiping out entire neighborhoods for miles and causing death in mere seconds. Often warnings go unheard in the middle of the night when people in its path are sound asleep. That’s when tornadoes are most deadly. Tornadoes occur most often in the Southeast and Midwest, east of the Rockies during spring and summer. But it’s not only a Plains states phenomenon. No matter where you live, there’s a risk for tornadoes to form. Our recent extreme weather patterns have produced tornadoes from New York to California. If you live in hurricane territory, then you know that tornadoes can form as the storm moves inland. Tornadoes can strike in the middle of the night with seemingly no warning because the people in their paths are asleep. And tornadoes aren’t restricted to what’s known as “tornado alley” in the middle of the country. Any of these misconceptions can be deadly, but together, they explain exactly why state and government agencies want every home equipped with a desktop or emergency crank weather alert radio.

If you do it outdoors, don’t do it without a portable weather radio

Think outdoor sports or hunting gets your adrenaline pumping? Just see what happens when severe weather pops up taking you and your buddies by surprise. No camping, hunting or sports gear pack should be without a portable weather radio. Whether you’re spending a few hours or a few days outside, a portable weather radio is a must-have. Batteries die. Data carrier coverage can be spotty in places. Any technology or gadget has the potential to fail when you need it most, but a Midland portable weather radio is tried and true. That’s why serious outdoor sports enthusiasts and outdoorsmen consider Midland the best weather radios out there.