How many times have you seen "The Wizard of Oz" and Dorthy getting swept up by the tornado ripping through Kansas farmland? Or "Twister", remember the team of Oklahoma storm chasers and university professors trying to insert an experiment into F4 and F5 tornadoes – one also swallowed a cow? Movies like these created the reputation of Tornado Alley as the tornado generator. Many hear the term think "Tornado Alley" has the most and strongest tornadoes. Let's find out if that's true…
1) Where is tornado alley?
There is no scientific designation of "Tornado Alley" but most people are referring to a stretch from the Great Plains to the Midwest.
The term was coined by two Air Force Weather Officers. On March 20, 1948 a tornado roared across Tinker Air Force Base near Norman, OK. Airplanes flipped over, airmen injured, power lines downed and Major Ernest Fawbush and Captain Robert Miller said they had no warning.
March 25, 1948 Fawbush and Miller notice similar atmospheric conditions to the 20th and put out the first official tornado forecast. And, it verified, another tornado hit the base. Tornado forecasting was born in the U.S.!
The duo set up a project called "Tornado Alley" to study severe weather from Lubbock TX to Eastern Colorado to Nebraska.
2) Why are there so many tornadoes in Tornado Alley?
Check out the tornado alley graphic above. The red is a clash zone. Cold, dry (polar) air drops from the Canadian Rockies and West Coast – it is dense and heavy. Warm, moist air (subtropical) is pulled in from the Gulf of Mexico. Warm, humid air is less dense than cold and dry air, but it's chock-full of potential energy. Think of the cold, dry (dense) air as the snowplow and the warm, moist (less dense) air as snow. The plow digs under the snow nd pushes it up, no contest. The clash begins.
Check out the or low pressure center on the lee side of the Rockies. So often we see disturbances (chunks of energy) or western storms fall apart high over the Rocky Mountains only to have it re-organize of the Rockies. The Low is the match or energy that sets off the explosion between the Battle of the Air Masses. Check out the specifics on tornado formation.
This battle can happen anywhere, but this is a classic storm scenario in the U.S.
3) Are tornadoes in Tornado Alley different from tornadoes in other areas?
Tornadoes are the same meteorological phenomenon whether they happen in Tornado Alley, New York, or Italy. The Alley has been very well studied and photographed through the years which adds to its reputation. For example, Oklahoma sees almost 2/3s of its tornadoes in April and May historically. NOAA's Storm Prediction Center gives advanced notice of the possibility of severe weather — sometimes up to 4 days out. Here is an example. So if a scientist wants to run an experiment or a photographer wants footage, the probability of finding a tornado is higher there. Tornados here are most likely in the spring with a second season in the fall.
A Washington Post article also surmised that studying, seeing and photographing tornadoes is easier in the Plains with flat landscapes and few trees. Weather conditions also make tornadoes hard to capture in other tornado prone areas like the Gulf Coast. "Thunderstorms along the Gulf Coast generally form in highly humid environments, resulting in lower cloud bases that can obscure a storm’s structure. Heavy rainfall frequently shrouds any tornadoes that do form. They’re rain-wrapped twisters impossible to photograph. Moreover, thunderstorms in the South are usually quicker-moving.
"With lower cloud levels and [faster storms], essentially they don’t see the tornado coming until it’s right on them," the article surmised.
4) Is this the only Tornado Alley?
The South and Gulf Coast have an "alley" too. It’s nicknamed Dixie Alley and refers to Louisiana, Arkansas, Mississippi, Alabama, Georgia and Tennessee. Like Tornado Alley, Dixie Alley is not a scientific description of an area. The National Severe Storms Forecast Center Director started referring to the area as Dixie Alley after a February 21, 1971 deadly tornado outbreak which spawned nine long-track tornadoes and killed 121 people. Southern tornado season runs generally from September to May.
An American Meteorological Society Bulletin said, "Research shows there are no tornado risk areas statistically separate from Tornado Alley, but there are large portions of the Southeast that experience more tornadoes than the rest of the country. It appears that Tornado Alley and Dixie Alley are part of a single large region of high tornado risk with a relative minimum near the middle due to the Ozark and Ouachita Mountains. Placement of the maximum tornado density in Mississippi, along with other regions of relative maxima across the Southeast, may warrant modification of the traditional tornado risk map that focuses only on the Great Plains. Understanding such patterns is important for preparing the public and mitigating tornado hazards." Tornado Days per Year map (below) shows a huge area of the U.S. experiencing one or more tornadoes within 25 Miles per year not just in Tornado Alley.
5) Where was the deadliest tornado?
Of the top 10 deadliest tornadoes in the U.S., only one occurred in Tornado Alley lists the Storm Prediction Center.
- Missouri, Illinois, Indiana Tri-State region on March 18, 1925 killed 695
- Natchez, MO on May 6, 1840 killed 317
- St. Louis, MO on May 27 1896 killed 255
- Tupelo, MS on April 5, 1936 killed 216
- Gainesville, GA on April 6, 1938 killed 203
- Woodward, OK on April 9, 1947 killed 181
- Joplin, MO on May 22, 2011 killed 158
- Amite, LA to Purvis, MS on April 24, 1908 killed 143
- New Richmond, WI on June 12, 1899 killed 117
- Flint, MI on June 8, 1953 killed 116
6) What is the longest tornado?
The longest tornado path record is held by our deadliest tornado. The Tri-state (MO, IN, and IL) tornado on March 18, 1925 traveled at least 218 miles over 3.5 hours according to the Guinness Book of World Records. That means the twister was moving at 62 mph on average. The NWS says winds exceeded 300 mph at times, and it was ¾-1 mile wide.
7) What is the record number of tornadoes in an outbreak?
Take another look at the Tornado Alley "set-up" graphic. That represents a single storm system which can touch off multiple tornadoes over several days. That’s called tornado outbreak. A record 362 confirmed tornadoes struck between April 25-28, 2011. The NWS says, "April 27, 2011, likely remains the "deadliest day for tornadoes" in the last 85 years. And, the event as a whole killed more people than any outbreak since 1936, when 454 individuals died."
The outbreak ravaged a dozen states from Texas to Wisconsin to the Carolinas. Three EF5 tornadoes, 12 EF 4, and 21 EF 3 caused about $12 billion in damage.
May 2004 holds the record for number of tornadoes in a month, 542.