More frequent and damaging storms are expected to increase, especially as population grows in the areas where tornadoes tend to hit in southeastern US states. The relevant US government agencies have been asked to focus more research on the causality between climate change and tornado as well as hurricane severity. JL
John Allen reports in USA Today:
Observations suggest an eastward shift in tornado frequency in recent decades and increasing frequency of tornadoes outbreaks, though the ties to climate change are as yet uncertain. Climate projections for the late 21st century have suggested that the conditions favorable to the development of the severe storms that produce tornadoes will increase over North America, and the impact could be greatest in the winter and fall. Projections suggest increases in severe storms in fall and winter of 16% to 25% relative to nowStorms on Friday night into Saturday morning produced a tornado outbreak across Arkansas, Illinois, Kentucky, Missouri, Mississippi and Tennessee. The National Weather Service’s Storm Prediction Center issued a moderate risk outlook with potential for significant tornadoes over the region, including expectations of strong and long-track tornadoes. As the event unfolded with many tornado warnings, at least one storm prompted a tornado emergency, a warning reserved for strong tornadoes likely to produce significant damage and fatalities and expected to move into a highly populated area.
Though official surveys will likely take weeks, preliminary data identified dozens of tornado reports across the region. Sadly, we already know that there were many fatalities and many more injuries, and in the coming days this toll will grow, particularly from the extremely long-tracked tornado or tornadoes that tracked from near Jonesboro, Arkansas, to Bremen, Kentucky.
While we can speculate about the intensity of the tornadoes, or that this might be one of the longer tracks ever recorded, official ratings will take time.
Preliminary indications suggest that there could be more than 200 miles of tornado damage to survey from the single storm that struck Mayfield, Kentucky. There are also several other paths being investigated.
Was this storm unprecedented?
In coming days, meteorologists from National Weather Service offices and damage survey experts will forensically assess each home, structure and other tornado-impacted objects and post-analyze how intense the tornadoes were, how many tornadoes occurred, and their path length and width. Then NWS offices will deliberate over the ratings for the event and release an official statement. This process, however, can begin only once recovery and safeguarding those impacted by this terrible event are complete.
The focus, for now, will be on mourning those lost and assisting in the recovery for people affected in the lead-up to the holiday period.
Was this storm and event unprecedented? Historically, tornado outbreaks have occurred on nearly every day of the year – if the conditions are right, any day can produce devastating tornadoes. We know that long-track tornadoes have occurred in the past with path lengths exceeding 100 miles.
The longest single-track tornado traveled an extraordinary 219 miles across Missouri, Illinois and Indiana – the "tri-state" tornado of March 18, 1925 – and killed 695 people, injuring thousands.
We also know that many of what were thought to be single tornadoes in history turned out to be families of tornadoes.
Whether the longest tornado track for this event is a record or is discontinuous remains unknown; damage on the ground will reveal what happened. Even if it wasn’t just a single tornado, this doesn’t diminish the impact of a long-track tornado at night, which we know produce significantly more fatalities. If this tornado were to be rated an EF5 with winds in excess of 200 miles per hour, it would be one of the rare few that have occurred outside of the spring months typically associated with tornado season. December, though, is no stranger to EF5s. On Dec. 18, 1957, Sunfield, Illinois, was destroyed by one.
While a rating is sometimes used to ascribe importance to an event, we need to remember that for those impacted, the tornado rating matters little, and people’s lives will never be the same for what they have experienced and lost. EF2-EF4 events have produced no shortage of damage, injuries and fatalities.
Does climate change play a role?
Significant tornado events outside typical tornado season raise the question of whether climate change may have played a role. Event-based attribution for climate change is still in development, particularly for tornadoes that need fine scales to model. Given the historical precedent, it would be misleading to definitively state a relationship to climate change without further assessment.
Even so, there are potential signs. Observations suggest an eastward shift in tornado frequency in recent decades and increasing frequency of tornadoes in outbreaks, though the ties to climate change are as yet uncertain. Climate projections for the late 21st century have suggested that the conditions favorable to the development of the severe storms that produce tornadoes will increase over North America, and the impact could be greatest in the winter and fall.
New research has also identified that these changes might be more rapid than we thought. Projections suggest increases in severe storm environments in fall and winter of 16% to 25% relative to now, per degrees Celsius of warming.
How this will impact tornado frequency or intensity remains uncertain, but even with frequency remaining static, the expansion of built-up areas in the frequently impacted southeastern USA is seeing increasing tornado vulnerability.
There have been no EF5-rated tornadoes since 2013. This year, we are running below the average of 1,368 a year, with 1,230 preliminary tornadoes through Saturday. As recent events demonstrated, it can all change in a single day.
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