NOAA study shows pattern of fewer days with tornadoes, but more tornadoes on those days

A massive tornado approaches Moore, OK on May 3, 1999

Are tornadoes increasing? Not really, the number has remained relatively constant. What is changing is that there are fewer days with tornadoes each year, but on those days there are more tornadoes, according to a NOAA report published today in the journal Science.

NOAA researchers looked at records of all but the weakest tornadoes in the United States from 1954 to 2013 for the study, “Increased variability of tornado occurrence in the United States.” They found that although there are fewer days with tornadoes, when a tornado does occur, there is increased likelihood there will be multiple tornadoes on that day. A consequence of this is that communities should expect an increased number of catastrophes, said lead author Harold Brooks, research meteorologist with the NOAA National Severe Storms Laboratory.

“Concentrating tornado damage on fewer days, but increasing the total damage on those days, has implications for people who respond, such as emergency managers and insurance interests,” Brooks said. “More resources will be needed to respond, but they won’t be used as often.”

Why tornadoes are concentrating on fewer days is still an open question, Brooks said. The pattern may be connected to changes in weather and climate. More research involving climate and tornado scientists is needed.

The study also showed there is greater variability in the starting date of spring tornado season, with more early starts and late starts in recent years. From 1954 to 1997, 95 percent of the time tornado season started between March 1 and April 20. But in the last 17 years, this happened only 41 percent of the time.

Researchers note tornadoes differ from tropical cyclones or hurricanes in the North Atlantic because tornadoes can occur year round. In fact, tornadoes have occurred in the U.S. on every calendar day at some point during the past 60 years.

Recent experience illustrates the study’s findings of variability. The study looked at tornadoes rated EF1 or higher on the Enhanced Fujita Scale, a measure of the damage caused by tornadoes with categories from EF0 to EF5. From June 2010 to May 2011, there were 1,050 EF1 and stronger tornadoes, the most in any 12-month period on record. Shortly after that, the U.S. saw the fewest in a 12-month period, only 236 EF1 and stronger tornadoes occurred from May 2012 to April 2013. November of 2012 had no EF1 tornadoes, but November of 2013 had the sixth most on record, with 66. There have been a relative low number of tornadoes to date in 2014, with an estimated 800 tornadoes of all intensities reported through September, almost 400 tornadoes below what is considered a normal year.

The study’s results are a first step toward understanding the relationship between changing tornado activity and a changing climate. The next step will be for climate scientists and tornado researchers to work together to identify what specific large scale pattern variations in climate may cause, or are related to, clustering of tornado activity.

Co-authors of the study are Gregory Carbin and Patrick Marsh with the NOAA’s National Weather Service Storm Prediction Center.

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Mathcounts competition

(Left to right - front row) Katherine Brooks, Vincent Li, Daniel Lamothe, Aniket Dehadrai, and Howard Zhong. Aniket and Howard qualified for Nationals. (Back row) Gaylon Pinc from the Oklahoma Society of Professional Engineers and Chair of OK Mathcounts program, head grader, and Harold Brooks.
(Left to right – front row) Katherine Brooks, Vincent Li, Daniel Lamothe, Aniket Dehadrai, and Howard Zhong. Aniket and Howard qualified for Nationals. (Back row) Gaylon Pinc from the Oklahoma Society of Professional Engineers and Chair of OK Mathcounts program, head grader, and Harold Brooks.

Whittier Mathcounts team going to Nationals
The Whittier Middle School Mathcounts team, coached by Katherine Brooks (assisted by Harold Brooks) won the state championship last weekend! Katherine is a pre-engineering teacher at Whittier Middle School, and both Katherine and Harold have volunteered their time to help the kids prepare for the competition over the last three years. The team was also honored for being “the most improved.”

Two students from the Whittier team, and two from Jenks Middle School in Jenks, OK will represent Oklahoma at Nationals in Orlando, FL on May 9. Katherine will coach the Oklahoma team, and Harold will help.

The MATHCOUNTS Foundation is a 501(c)(3) non-profit organization that strives to engage middle school students of all ability and interest levels in fun, challenging math programs, in order to expand their academic and professional opportunities.There are 224 final Mathletes from 50 U.S. states, U.S. territories, State Department schools and Department of Defense schools.

Congratulations and good luck!

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Record low estimated tornado counts from May 2012 to April 2013

Tornado in Wyoming
Tornado in Wyoming

NSSL tornado climatology expert, Harold Brooks has written a blog post about the remarkable absence of tornado activity during the 12-month period from May 2012 to April 2013. The estimated number of EF-1 or stronger tornadoes for this period is 197, a record low.

Brooks compared the current 12-month period with previous (E)F1 or stronger tornado counts back through 1954. He found the previous low for (E)F1 and stronger tornadoes in a 12 consecutive calendar month period was 247, from June 1991-May 1992.

This apparent record was set less than two years after the record for most EF1+ tornadoes in a 12-month period was set, with 1050 from June 2010-May 2011.

Read the full post here:  U.S. Severe Weather Blog.

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Two NSSL researchers elected AMS Fellows

Dave Rust (left) and Harold Brooks

The American Meteorology Society (AMS) has announced the election of two NSSL researchers to the status of AMS Fellow. Awardees will be honored at the AMS Conference January 23-27, 2011 in Seattle, Wash.

W. David Rust, NSSL Physical Scientist has been elected an AMS Fellow.  Rust has been with NSSL since 1976 and is an expert in severe storm electricity research, pioneering the use of free-flying weather balloons. He currently serves as the Director of the Field Observing Facilities Support group.

Harold E. Brooks, NSSL Atmospheric Scientist, was also elected an AMS Fellow.  Brooks leads the Mesoscale Applications Group at NSSL, and has conducted extensive research on the climatology of tornadoes.  He has been with NSSL since 1992.

Those eligible for election to Fellow have made outstanding contributions to the atmospheric or related oceanic or hydrologic sciences or their application during a substantial period of years.

Rust and Brooks join eight current NSSL scientists (Burgess, Doviak, Jorgensen, Zrnic, Kimpel, Davies-Jones, Lewis and Stensrud) and five retired scientists (Kessler, Maddox, Holle, Kimpel and Davies-Jones) honored with this distinction.

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