March 2 - 3 tornado outbreak: 10th largest in recorded history?

The deadly early-season tornado outbreak of March 2 - 3 that hit Indiana, Kentucky, and surrounding states, killing 41 people, may have been the 10th largest two-day tornado outbreak since record keeping began in 1950. NOAA's Storm Prediction Center now lists 132 preliminary tornado reports for March 2, and 11 for March 3. It typically takes several months to finish damage surveys and verify all the tornadoes that really occur in a big tornado outbreak. Sixty-one tornadoes have been confirmed so far, according to Wikipedia's tally of the outbreak. The two-day total of 143 tornadoes from March 2 - 3 is probably an over count of about 15%, based on historical levels of over counts. This would give the March 2 - 3 outbreak around 120 tornadoes, making it the tenth largest outbreak since record keeping began in 1950. Assuming this is true, the past two tornado seasons would hold four of the top ten spots for largest tornado outbreaks in recorded history. Below are the top two-day tornado outbreaks since 1950. Several of these two-day totals were taken from outbreaks that lasted three or more days; the highest two-day period of activity was selected for this list, so that the outbreak would not be mentioned multiple times. The numbers from the 2011 outbreaks are still preliminary:

262, Apr 26 - 27, 2011
169, Apr 3 - 4, 1974
160, May 29 - 30, 2004
141, May 24 - 25, 2011
135, Jan 21 - 22, 1999
130, Apr 15 - 16, 2011
125, May 4 - 5, 2003
123, Jun 15 - 16, 1992
121, May 4 - 5, 2007
120ish, Mar 2 - 3, 2012
120, May 3 - 4, 1999


Video 1. Spectacular tornado video taken at a home in West Liberty, Kentucky outfitted with seven automatic security cameras, which captured the fury of the strong EF-3 tornado with 165 mph winds that roared overhead on March 2, 2012. The views from all the cameras are worth watching, but don't watch past 7:00, as the end of the video has three minutes of blankness at the end. According to an article at wkyt.com, the home owners, Randy and Norma Risner, took shelter in the basement, and their home survived the tornado. "You could actually feel the ground shaking and our the 11-foot basement walls were shaking, too," Norma said. The tornado destroyed their workshop (caught on camera), and another camera shows the roof of their neighbors home peel off.


Video 2. Perhaps even more impressive is video taken at a nearby pharmacy showing the West Liberty tornado destroying buildings across the street. The view from Clinic Pharmacy starts at 0:50 into this video.

The uncertain business of counting tornadoes
While there's no question that having four top-ten tornado outbreaks in just two years is highly unusual, the quality of our tornado data base is poor, and there are probably outbreaks that occurred prior to 1990 that were significantly under-counted and would have made the top ten list, had they occurred today. The number of tornadoes being reported has increased in recent decades, and this increase may be due entirely to factors unrelated to climate change:

1) Population growth has resulted in more tornadoes being reported.

2) Advances in weather radar, particularly the deployment of about 100 Doppler radars across the U.S. in the mid-1990s, have resulted in a much higher tornado detection rate.

3) Tornado damage surveys have grown more sophisticated over the years. For example, we now commonly classify multiple tornadoes along a damage path that might have been attributed to just one twister in the past.


Figure 1. Number of EF-1, EF-2, EF-3, EF-4 and EF-5 tornadoes from 1950 to 2011. The total shown for 2011 is preliminary and uses unofficial numbers, but 2011 now ranks in 2nd place behind 1973. There is not a decades-long increasing trend in the numbers of tornadoes stronger than EF-0, implying that climate change, as yet, is not having a noticeable impact on U.S. tornadoes. Data provided by Harold Brooks, NOAA/National Severe Storms Laboratory.

If we look at changes in the strongest tornadoes--EF-1, EF-2, EF3, EF4, and EF-5 twisters, the ones most likely to have a reliable long-term detection rate, due to their destructive power--we see no sign of an increasing trend in recent decades (Figure 1), even if we include 2011. However, it is difficult to make solid conclusions on how tornadoes may be changing, since the quality of the historical tornado data set is so poor. This is largely due to the fact that we never directly measure a tornado's winds--a tornado has to run over a building before we can make an EF-scale strength estimate, based on the damage. As tornado researcher Chuck Doswell said in a 2007 paper, "I see no near-term solution to the problem of detecting detailed spatial and temporal trends in the occurrence of tornadoes by using the observed data in its current form or in any form likely to evolve in the near future." Major changes in the rating process occurred in the mid-1970s (when all tornadoes occurring prior to about 1975 were retrospectively rated),and again in 2001, when scientists began rating tornadoes lower because of engineering concerns and unintended consequences of National Weather Service policy changes. Also, beginning in 2007, NOAA switched from the F-scale to the EF-scale for rating tornado damage, causing additional problems with attempting to assess if tornadoes are changing over time.


Figure 2. Thomas Hudson and the Portlight trailer in Harrisburg, Illinois.

Portlight disaster relief charity responding to the tornado disaster
The Portlight disaster relief charity has made a strong showing in tornado-devastated Harrisburg, Illinois and Henryville, Indiana. Both towns were hit by deadly EF-4 tornadoes during the February 28 - March 3 tornado outbreak. From the Portlight blog:

"Yesterday we went to Henryville, Indiana and volunteered for a few hours, mainly unloading trailers with water, canned goods, etc.

The people were in great spirit, eager to rebuild, and overall thankful that it wasn't worse than it was.

Myself, Jeremiah Moran, Blaize Edwards, and Andrew Newcomb made the 2 hour drive from Washington, Indiana.

We will be trying to get back this weekend or a couple of days next week."

An interesting sciencedaily.com article discusses how the powerful EF-4 tornado from the February 29, 2012 outbreak that devastated Harrisburg, Illinois passed through a high-density network of seismographs. "The seismograms show a strong, low-frequency pulse beginning around 4:45 a.m. on Feb. 29. Our preliminary interpretation, based on other seismic records of tornadoes, suggests that we were recording not the tornado itself, but a large atmospheric pressure transient related to the large thunderstorms that spawned the tornadoes."

I'll have a new post by Wednesday.

Jeff Masters