With an average November tornado tally of 58 (1991-2010), we are in near-record low territory for the month.
Only four other years in records dating back to the 1950s have witnessed comparably low tornado activity in November according to Harold Brooks, a tornado expert with NOAA’s National Severe Storms Laboratory. 1976 had zero tornadoes, 1954 had two, and three occurred in 1980 and 2009, he said.
Tornadoes happen all year, but there are two seasons where activity tends to peak.
Spring is prime time for tornado activity. That’s when fresh bubbling warmth dances with winter’s remnant cold as dry air masses spill over the Rockies. Put a powerful jet stream overhead and light the dynamite. Rotating storms dot the land, dropping tornadoes in their wake.
A second tornado peak, one which is certainly more erratic, comes along during the fall. In something of a reverse of the process during spring, the jet stream again targets the country as the calendar changes from summer to winter.
This so-called “second season” tends to be at its peak in November.
But this year, tornadoes have all but vanished.
So, what’s up? Where is the second season? The thing about second season is it’s highly variable to begin with.
“Novembers are flood or drought months for tornadoes,” Brooks said. “[A]pproximately one-third of all the November tornadoes occur in just six of the 62 years and half in 11 years.”
This year a historic drought in precipitation over the Southeast can be implicated in the tornado drought.
The normally stormy Southeast is typically tornado territory at this time of year according to Brooks. But if there are no storms, there won’t be tornadoes, he said.
This hostile pattern for tornadoes has expanded well beyond the Southeast
Much of the U.S. has been unfriendly to tornadoes as far back as late summer. The jet stream, which helps energize tornadoes, has mostly remained over Canada. That’s normal during summer but much more rare deep into fall.
Instead, a giant ridge of high pressure has frequently blocked the jet stream from diving southward, protecting much of the U.S. from significant storminess and giving to rise to much above normal temperatures.
“The big player since September and even late summer in terms of synoptic pattern has been the persistent ridging over the Plains and Southeastern United States,” said John Allen, a pioneer in seasonal tornado forecasting and professor at Central Michigan University.
This unusually strong and persistent high pressure system has stymied storm systems that may have otherwise sparked a tornado risk in parts of the central United States.
“This [pattern] has led to anomalous warmth across the Plains, which Harold Brooks has shown to be a generally negative contribution for tornado frequency,” said Allen.
Not only is November set to make history for low tornado activity, but also 2016 as a whole.
Tornado numbers this year now rank near the bottom of estimated counts.
These lower-than-normal numbers, while historic, are also in some ways fairly characteristic of years in which an El Niño event wanes and La Niña takes over.
“The year in general has been considerably below normal (around 1000 tornadoes), which is not unexpected given the influence of the El Niño that persisted into spring, diverting the polar storm track northwards, and leading to a very quiet May,” John Allen wrote.
Might climate change play any role in the low numbers? While hesitant to draw too many long-term conclusions, Allen as well as Victor Gensini, a professor of meteorology at the College of DuPage, both wondered about extreme lows in Arctic sea ice and this spate of no tornadoes. Past studies have shown there to be a tie between unusual jet stream behavior (#jetweirding) and climate change.
While noting the important role natural variability plays in tornado activity and an absence of a long-term trend, Gensini said: “[I]t is certainly plausible that a lack in Arctic sea ice this year has had implications for cyclone track and intensity.” In other words, if climate change shifted the storm track north, it might be partially responsible for the lack of twisters.
Finally, lest we let our guard down and prematurely celebrate a year with few tornadoes and near-record low tornado fatalities, we shouldn’t forget what occurred in December 2015.
Entering that final month of last year, there were a record-low 15 tornado deaths. Then waves of tornadoes struck the South and the yearly toll jumped. With a more energetic weather pattern ahead, we should always stay prepared and remember that droughts won’t last forever.