Twisters Give Nation a Pass in 2015: Lowest Death Toll on Record?

Amid all the genuinely awful news making the rounds in recent days, here is one bright spot: the year 2015 may end up with the lowest number of U.S. tornado fatalities in at least 141 years. As of December 2, preliminary numbers from the NOAA Storm Prediction Center show only 10 tornado-related deaths nationwide. If this number holds through the end of the year, it will beat the 12 deaths reported in 1910 to become the lowest annual total on record. NOAA/SPC keeps tabs on tornado statistics, including fatalities, back to 1950. For earlier periods, veteran researcher Thomas Grazulis (author of the definitive volume “Significant Tornadoes 1680-1991”) has combed through newspapers and other archives to come up with the best existing data on tornado occurrence and fatalities as far back as 1875. If anything, the Grazulis numbers may be on the low side, which gives added confidence that the nation has indeed seen a remarkably safe year tornado-wise in 2015. The year is not done, though: 5 of the last 10 Decembers produced at least one tornado fatality, with the highest total of that period being 9 in December 2010.


Figure 1. Tornado deaths are far below the levels observed prior to the advent of the National Weather Service watch/warning system in the 1950s, although the catastrophic tornadoes of 2011 produced the biggest spike in fatalities in more than 80 years. Data provided courtesy Harold Brooks, NOAA National Severe Storms Laboratory; data sources are NWS (1950 – 2015) and Thomas Grazulis (1875 – 1949).


Figure 2. The EF4 tornado that plowed across northern Illinois just west of Chicago on April 9, 2015, photographed near Stillman Valley, Illinois. Image credit: wunderphotographer StormyPleasures (Charles Russell).


Figure 3. Wreckage lies along Illinois State Highway 64 near Rochelle, Illinois, on April 10, 2015, after an EF4 tornado struck the previous night. Image credit: Jon Durr/Getty Images)

Northwest flow cuts down on strength, frequency of tornadoes
Part of the story this year is sheer good luck. The strongest tornado of 2015 so far occurred on April 9: a violent EF4 twister that tracked over 30 miles of northern Illinois just west of Chicago. Just a small shift in that tornado’s track could have produced far more havoc. And the unseasonably late tornadic swarm of November 16 over the southern Great Plains produced three large EF3 tornadoes but comparatively little damage. Apart from these two outbreaks, the year’s crop of tornadoes was generally on the weak and short-lived side. A single outbreak can make an otherwise quiet year devastating, but in general, “a low number of tornadoes correlates to a low number of tornado deaths,” noted Greg Carbin, warning coordination meteorologist at NOAA/SPC, in an email.

After the horrific tornado season of 2011 (with 553 fatalities, the nation’s deadliest since 1925), the U.S. has seen four consecutive years with below-average activity, if we count 2015 in advance. For this quietude, we can thank the same predominant upper-level pattern that’s stoked four years of intense drought in California and shunted a large fraction of hurricanes away from the East Coast. “The stagnant large-scale pattern of generally northwest flow that has dominated central North America for the past few years has certainly played some role in suppressing conditions more supportive of tornado outbreaks,” Carbin said. “Whether this shift to more tranquil conditions is part of some longer-term oscillation, a result of climate change dynamics, or both, or just a random occurrence, is hard to say.”



Figure 4. The number of tornadoes in 2015 thus far is running about 25% below the 1954-2007 average for this time of year, when adjusted for multiple initial reports and for tornado “inflation” (the increased likehood in more recent years that a given tornado is documented). Image credit: NOAA Storm Prediction Center.

An uptick in tornado deaths over the last decade
Naturally, given the nature of his job, Carbin worries about the possibility that a quiet stretch could soften people’s resolve to keep themselves and their loved ones safe from tornadoes. The decade from 2005 to 2014 produced a total of 1092 tornado-related deaths. That’s roughly double the death rate that prevailed over the three prior decades (1975-84, 1985-94, and 1995-2004). Clearly, the numbers for the past decade are skewed by the huge death toll in 2011, but a total of six of the ten years in 2005-2014 produced at least 50 deaths. That wasn’t the case in any of the three previous decades.

“The annual death toll in the modern era is likely influenced more by the number of tornadoes than by our improved ability to predict them,” Carbin emphasized. “The conditions to support a widespread killer tornado outbreak can come together in a matter of 2-3 days. We need to maintain vigilance!”

Paris negotiations plow ahead
Diplomats from around the world continue to work on a 54-page draft of the agreement that organizers hope to finalize and adopt next week at the UN climate summit in Paris. One of the biggest points of difference right now is the maximum amount of global warming that emission cuts should allow for. The idea of keeping global temperature rise to no more than 2.0°C above preindustrial levels has been widely--but not universally accepted--for many years. There is nothing “magic” about 2.0°C, as significant impacts can be expected even at lower amounts of warming, and the effects would get progressively worse at higher amounts of warming. A group of nations now numbering more than 100 has been pushing for a maximum of 1.5°C rather than 2.0°C, a move that has gained momentum as well as resistance. We’ll have more on the Paris negotiations next week; in the meantime, I’ll be discussing the summit on Friday and through next week on the Weather Channel’s Weather Underground program (#WUTV). These segments will air at 6:40 pm EST on most if not all days.

Have a great weekend, everyone!

Bob Henson