What Disaster Models Tell Us About U.S. Tornado Risk

This week’s deadly tornadoes in the South cut a swath of devastation through several states. The disaster also brought a shattering end to what had been a relatively quiet start to the usual peak U.S. tornado period. We asked Matthew Nielsen, director of RMS model product management, about the company’s tornado models and what they say about the rest of this year’s tornado season.

Q: What did RMS modeling reveal going into the 2014 tornado season?

Nielsen: RMS modeling revealed the elevated risk found in areas of the Southeast, specifically the heightened tornado risk from long-track storms. We tend to find that while the frequency of tornadoes in states like Alabama, Arkansas, and Mississippi is not as high as states in the Tornado Alley, the tornadoes that do occur in these states tend to persist much longer on the ground and affect more exposure.

Q: What is the general financial and economic impact of tornadoes as compared to other catastrophes?

Nielsen: Tornadoes tend to have very high damage ratios, meaning that most locations in its path will suffer extreme to total damage. If a tornado hits an exposure center with high-value commercial or industry risks, losses can easily pass the $1 billion mark. While tornadoes tend to have much smaller and more focused paths than hurricanes, they can inflict heavy losses to the exposure they affect, and have historically been known to cause losses in excess of $2 billion to $3 billion for a single tornado track.

Q: What has made the current tornado outbreak span multiple days and multiple regions?

Nielsen: The current outbreak has persisted for several days over a very similar region due to the very slow moving nature of the low-pressure system. This is also related to the persistence and stubbornness of the atmosphere this season. Given the overlapping areas of intense thunderstorms over the last few days, flash flooding is becoming more of an issue due to repeated periods of intense rainfall.

Q: Based on the information available, what’s in store for the rest of the season after having a slow start but recently picking up steam?

Nielsen: On one hand, the storm door may now be open, and we could see a very active May. We are now reaching the climatological peak of the severe convective storm season; May is typically the highest activity month in the U.S. The overall weather pattern over North America has been very stubborn and persistent this year, as we saw with the frequency and duration of cold weather over the eastern half of the continent, and warm, dry weather over the west coast. It is possible that activity may continue at this heightened pace for several weeks.

Conversely, given how quickly it went from active to inactive over the last week, it could also transition back to a relatively quiet phase for the next few months. There is a lot of uncertainty as to how the rest of the season may play out.

As the season progresses, we should start seeing more activity over the traditional Tornado Alley states, with less activity over the Southeast U.S. Activity this time of year is usually more focused around the southern Plains states like Oklahoma, Kansas, and Texas. Arkansas, Alabama, and Mississippi usually experience their activity peaks in the late winter to early spring months of February and March.

Matthew is a meteorologist and geographer with extensive experience in catastrophe risk in North America. At RMS, he is responsible for the development of the RMS climate-peril models for the Americas, including the severe-convective storm, winter storm, flood, wildfire and hurricane models. He has conducted field reconnaissance for major catastrophes including Hurricane Katrina in 2005, the Greensburg tornado in 2007, the Tuscaloosa-Birmingham tornado in 2011 and Hurricane Sandy in 2012.  Matthew has been instrumental in regulatory outreach for RMS in the U.S. He liaises regularly with regulators in 15 states to establish open channels of communication about the use of RMS models and solutions. Prior to RMS, Matthew was a graduate research assistant at the Cooperative Institute for Research in the Atmosphere (CIRA) where he authored a thesis on remote sensing in satellite meteorology.  

Matthew holds a master’s degree in atmospheric science from Colorado State University and a bachelor’s degree in physics from Ripon College, where he won the Henry Knop Award in Physics. 

He is a member of the American Meteorological Society (AMS), the International Society of Catastrophe Managers (ISCM), and the American Association of Geographers (AAG).