Tornado Shelters, More Important than Ever
While there isn’t a long-term trend in the number of U.S. tornadoes stronger than EF0, several recent studies suggest the time distribution of those tornadoes and their tendency to cluster in outbreaks may be changing. And more activity means having a plan in place to survive a storm is more important than ever. And luckily, tornado shelters are less expensive and easier to install than in years past.
EF1 Tornado Days and Active Tornado Days
Fewer Tornado Days, But More Active Days
When eliminating EF0 tornadoes from yearly counts, which have steadily risen over the past few decades due to more extensive spotter networks, the implementation of Doppler radar, and advanced technology such as smartphones and social media, there is essentially no long-term yearly trend in the raw number of EF1 and stronger tornadoes.
However, the number of days with at least one EF1+ tornado in the U.S. has fallen from an average of 150 such days in the early 1970s to around 100 days in the first decade of the 21st century, according to an October 2014 study in the journal Science.
However, the study by noted tornado researchers Dr. Harold Brooks of the National Severe Storms Laboratory, Greg Carbin of NOAA’s Storm Prediction Center, and Dr. Patrick Marsh, also of NOAA/SPC, found the number of days with a large number of tornadoes is actually increasing over time.
“The frequency of days with more than 30 EF1+ (tornadoes) has increased from 0.5 to 1 days per year in the 1960s and 1970s to 3 days per year over the past decade,” says the Brooks et al. study.
In essence, we have fewer days with tornadoes, but are packing more of them into the days we have. “Approximately 20 percent of the annual tornadoes in the most recent decade have occurred on the three biggest days of each year,” says the Brooks et al. study. So knowing what to do when severe weather strikes, and ideally, having a residential storm shelter, a community storm shelter easily accessible in your city, or a corporate storm shelter or commercial tornado shelter at your business or school is more important than ever.
Another recent study by Dr. James Elsner not only found a similar clustering of tornadoes into fewer days, but also a spatial clustering of tornadoes on those very active days.
“It appears that the risk of big tornado days with densely concentrated clusters of tornadoes is increasing,” Elsner says in the July 2014 study.
Large Swings in Monthly, Yearly Numbers
These clusters cause more damage in a defined area. So instead of being concerned about a single rotation, and potentially feeling relieved after a tornado passes, it is extremely important to be more vigilant and aware of other tornadoes in the area. Residential tornado shelters and community storm shelters are the best option to protect yourself from these unpredictable storms.
For only the second time since 1950, the first three weeks of March 2015 passed without a single tornado anywhere in the U.S.
Yet as recently as 2011, almost 1,700 tornadoes ripped across the nation, including 349 tornadoes in a four-day outbreak from April 25-28, the costliest tornado outbreak in U.S. history.
While year-to-year variability has long been prevalent in U.S. tornado counts, a 2014 study by Dr. Michael Tippett found volatility, a term he uses for variability in tornado counts, has increased since 2000.
Furthermore, the Brooks et al. study found the tendency for more monthly extreme highs and lows in EF1+ tornado counts in recent years.
“Excluding the zero-tornado months, there are more extreme months in the most recent 15 years of the database (1999-2013) than in the first 45 years,” says Brooks et al. 2014.
In other words, we’ve seen extreme high monthly tornado counts (758 tornadoes in April 2011, for example) and extreme low monthly tornado counts (March 2015, for example) more often over the past 15 years, a trend that may continue.
Of course, low tornado count years do not preclude significant tornadoes or tornado outbreaks. Despite the lowest three-year tornado count on record from 2012-2014, we still had destructive outbreaks in March 2012, in May 2013 (Moore and El Reno, Oklahoma), and April 2014 (Vilonia, Arkansas).
When Tornado Season Shifts Into Gear, Skewing Earlier in the Year-The Time to Install an Above Ground Tornado Shelter is NOW
Tornadoes can occur any time of year the overlap of sufficient moisture, atmospheric instability — relatively cold, dry air aloft overlying warm, humid air near the Earth’s surface — and a strong source of lift such as a warm front, dryline, strong jet-stream disturbance occur.
Because of that, it’s difficult to define a tornado season on a national scale as distinctly as, say, a hurricane season.
However, Brooks et al. tracked as a metric the occurrence of the year’s 50th EF1+ tornado to get a sense of whether the timing of the ramp-up in U.S. tornadoes typically seen in spring is changing.
While the long-term average date (March 22) hasn’t changed, Brooks et al. found a marked increase in the number of “late-start” and “early-start” years since the late 1990s. The four latest starts and five of the ten earliest starts to the season all occurred in the 1999-2013 period. These range from late January (1999 and 2008) to late April (2002, 2003, 2004 and 2010).
In essence, even the date the season kicks into a higher gear is becoming more volatile-so don’t wait to install your tornado shelter.
Climate Change Role?
Now, the toughest question: Is climate change playing a role in the increasing variability of the nation’s tornadoes?
The short answer is, possibly.
The challenge in answering this question is linking short-fuse events like tornadoes and tornado outbreaks to long-term changes in atmospheric parameters generally conducive for severe thunderstorms, such as instability and wind shear.
Studies by Dr. Jeff Trapp and Dr. Noah Diffenbaugh, among others, suggest atmospheric instability, driven by increased moisture, is expected to be greater in a warming climate. However, wind shear, crucial for the formation of supercells which can produce the strongest tornadoes, may diminish overall, but may feature more days with higher wind shear.
Therefore, the overall environment may be more conducive for severe thunderstorms (with large hail and damaging winds), but it remains unclear whether the number of tornadoes or even strong tornadoes would necessarily rise in a warming world.
This brings up an interesting possibility, a seasonal outlook for severe weather, similar to hurricane season outlooks.
“I suspect that ultimately knowing if a severe weather season will be above, below, or near normal would be important for reinsurance portfolios as an increasing amount of money is spent on hail and wind claims,” said Dr. Patrick Marsh from NOAA/SPC.
The best advice is don’t think that you can predict the severity of tornado season or even when it begins, and definitely do not wait until after a storm strikes to realize the need to purchase a storm shelter. Tornado shelters of all sizes are more affordable than ever and Safe-T-Shelter even partners with local credit unions for financing. Everyone deserves the right to protect their family from unpredictable storms. So whether it is a residential storm shelter, a community storm shelter, a commercial storm shelter or a corporate storm shelter, Safe-T-Shelter can help, and our 20+ years experience means you can have confidence in our products and our longevity.