Are We Experiencing More Tornadoes?
(Or Does It Just Seem Like It?)
Against a stormy backdrop of lightning following a thunderstorm, the funneling power of a tornado can reach wind speeds over 300 mph, touch the earth causing mass destruction, levitate buildings, vehicles and debris, or create a sky column of water over a lake or ocean.
My first experience with tornadoes was when we moved from Hawaii to my husband’s home state of Minnesota, right after the nearby Wadena tornado of 2010. Previously, I had mostly viewed these severe storm phenomena in news reports with awe. Seeing how a tornado ripped a 1.5-mile-wide path through the heart of a small town turned fascination to fear. I had expected to encounter giant mosquitos that summer, but tornados definitely were not in my pre-arrival information!
First-hand knowledge of community devastation tornadoes made me a keen summer-weather watcher. Lately, it seems like there is an increase in the number of tornadoes, but there is still much we don’t know about them.
How Tornadoes Form
Most tornadoes form when high elevation winds in a supercell thunderstorm blow at an angle to wind blowing at the earth’s surface, creating friction. This causes an invisible tube of air to rotate horizontally. Meanwhile, rising air pushes the rotating air tube up vertically. Once this updraft of rotating air starts to draw warm, moist air from ground level, a tornado can form.
Weaker tornadoes can form from non-supercell thunderstorms. These “quasi-linear convective systems” (QLCS) usually form late at night or in early morning hours.
There are also waterspouts formed with spinning moisture over a body of water. These types of thunderstorms are also weak- EF2 or less. The EF stands for Enhanced Fujita- a measurement calculation that relates to wind speed. Tornadoes are rated from EF0 with winds from 65 – 86 mph, to EF5 with winds over 200 mph.
You can find more detailed information about types of tornadoes on the National Oceanic and Atmospheric Administration (NOAA) National Severe Storms Laboratory (NSSL) website.
What puzzles scientists is why a thunderstorm only spawns a tornado about 20% of the time. Is it temperature, wind direction or other factors? It seems once research detects a pattern, storms occur that don’t fit.
Is the Frequency of Tornadoes Changing?
While it might seem like there are more tornadoes, in part, it may be that experts are getting better at tracking and reporting these weather events. In the early days, severe storm information relied on eye-witness accounts. If it wasn’t seen or reported, the event was not included in historical data. It wasn’t until the early to mid-1990s that extensive Doppler radar technology expanded beyond the scientific research lab. Once Doppler training was made publicly available to meteorologists and others, there was a significant boost in severe storm and tornado forecasting.
Doppler radar was also a turning point for modernization of National Weather Service operations, providing improved public warnings and lead time. News coverage of severe weather events has also expanded and become more accurate. While on a road trip last summer, a tornado watch turned to a warning, tracking along the freeway we were driving along on the way back from Minneapolis. By following NWS alerts on my phone and listening to local radio broadcasts, we could safely make it home before the storm system crossed our path.
Storm chasers, which are science teams brave enough to follow tornados closely on the ground, capturing field data that radar cannot pickup, help to improve our knowledge of how tornadoes form and their composition. Most importantly, they relay information that increases early warnings, allowing people more time to get to a safe place.
Amateur storm chasers can be a dangerous impediment to this wild data gathering. They clog roadways and escape routes, putting scientific teams and the public that rely on their information, at risk, all for the thrill or chance to sell photos and videos to news outlets.
Other factors may make it seem like there are more tornadoes.
Twisters can happen in any state, but historically the most severe ones have occurred in the central US from Texas to southern North Dakota. This vertical corridor has been called Tornado Alley since the 1950s.
However, over the past 20 years, tornados have decimated parts of the Midwest and southern states. A 2018 study published in the journal Nature shows that the main swath of twisters is farther south and farther east than tornado alley, including increased activity in the Mississippi River Valley. So in those areas, you may see severe weather happen more frequently than before.
Another shift that is occurring is a marked increase in big tornado days featuring densely concentrated tornado outbreaks. Researchers at the University of Florida found that the number of days with multiple tornadoes occurring in a region is increasing, while the number of days with single or few tornados is decreasing.
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Can Change in Tornadoes be Related to Climate Change?
We are seeing a significant increase in extreme weather events all over the world, including an increase in the supercell thunderstorms that precede tornados.
Scientists can attribute many weather changes due to continued burning of fossil fuels, releasing a massive amount of carbon dioxide (CO2) in the atmosphere. This results in heating of the planet, or global warming. While it’s hard to pinpoint a direct correlation between climate change and increased tornado frequency, there is a relatable pattern of increased supercell thunderstorms directly related to our changing climate.
Preparing for “Tornado Season”
According to NOAA, “tornado season” is the period during which the United States experiences the highest incidence of tornadoes. In the southern Plains (comprising states such as Texas, Oklahoma, and Kansas), the peak season runs from May to early June, while it arrives earlier in the spring on the Gulf coast. Tornado season in the northern Plains and upper Midwest (encompassing states like Minnesota, Nebraska, Iowa, North and South Dakota) falls in June or July. Keep in mind tornadoes can happen any time of year or day, although they tend to occur more frequently between 4 and 9 p.m. They can also happen in other parts of the country. In March, Los Angeles was hit by the largest tornado that the state has seen in three decades. There have even been mild QLCS tornadoes and waterspouts in Hawaii.
The National Weather Service offers these tips if a tornado is approaching:
- Stay Weather-Ready: Continue to listen to local news or a NOAA Weather Radio to stay updated about tornado watches and warnings.
- At Your House: If you are in a tornado warning, go to your basement, safe room, or an interior room away from windows. Don’t forget pets if time allows.
- At Your Workplace or School: Follow your tornado drill and proceed to your tornado shelter location quickly and calmly. Stay away from windows and do not go to large open rooms such as cafeterias, gymnasiums, or auditoriums.
- Outside: Seek shelter inside a sturdy building immediately if a tornado is approaching. Sheds and storage facilities are not safe. Neither is a mobile home or tent. If you have time, get to a safe building.
- In a vehicle: Being in a vehicle during a tornado is not safe. The best course of action is to drive to the closest shelter. If you cannot make it to a safe shelter, either get down in your car and cover your head, or abandon your car and seek shelter in a low-lying area such as a ditch or ravine.
For more tornado safety information, see this National Weather Service page.
Preparation for extreme weather events like tornadoes, might also include a plan for your electronic devices that you depend on for communication. Arvig has an entire library of information on preventing damage to your electronic devices during extreme weather events and weather-related power outages. Stay safe out there!