When will we reenter an active severe cycle? (1 Viewer)

When will once again see large-scale outbreaks similar to those of 2008–14?


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warneagle

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I do wonder how much climate change is going to have on the distribution and intensity of tornadoes and tornado outbreaks; Grazulis posted some stuff on his Twitter that showed a trend that climate change might kill spring chasing, among other things. I wonder if tornadoes in America will shift locations as to areas where they most commonly occur (Dixie taking the Plains' place as the main hotspot for tornadoes, for instance) and maybe tornadoes and major outbreaks may not occur as often but when they do they will be much more powerful and intense (I think climate change has had that effect on hurricane frequency and intensity, actually). Perhaps violent outbreaks of tornadoes in unexpected places will happen more often? No clue, just thinking out loud.
I think we've certainly seen an increase in intense cool-season events (with the perpetual caveat that tornado counts are going to be higher now than they were in the past). That makes a lot of sense, since a warmer planet and a warmer Gulf would provide greater thermodynamic support in the cool season where there's usually going to be ample shear and lift regardless. Friday was a good example of this, with a crazy thermodynamic environment for areas that far north in mid-December. I would think that's the primary deterministic effect of climate change on tornadoes.

As far as the spring season goes, I've seen a few different ideas thrown around. Some people have said that the spring season may weaken because of decreased wind shear and upper level support, while other people have said that the issues may come from greater instability leading to less CIN (or rather enough instability to break the cap faster) and more widespread convection. We've seen the latter several times recently, where high-end environments were spoiled by early, excessive convection and messy storm modes (for example, 20 May 2019). I think it's probably harder to prove this is a deterministic effect though.
 

Kory

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Now that the recent +PDO trend since 2013 seems to be reversing itself, given -ENSO/-PMM in place as well, one may reasonably ask whether the background state will begin to favour large-scale outbreaks with multiple long-tracked supercells each producing one or more EF4+ tornadoes. By “active severe cycle,” I am referring to a period with outbreaks like those of 21–22 March 1932, 11–12 April 1965 (Palm Sunday II), 3–4 April 1974 (first Super Outbreak), 26 April 1991, 3 May 1999, 5–6 February 2008 (Super Tuesday), 27–28 April 2011 (second Super Outbreak), 24 May 2011, 27–28 April 2014, and so on. We have certainly seen significant events since 2014, but these have mostly been confined to localised, isolated, outstanding supercells that produce a violent tornado or two, rather than multiple, long-lived, violent families.
With 3 long track, violent tornadoes from Friday’s event, I think this has been firmly answered.
 
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This Wednesday looks like another situation in which a classic, low-amplitude solution seems to have turned into a forced, high-amplitude one, notwithstanding the -PDO/-ENSO/+TNI. There have been exceptions, but many large-scale events turned out to be relatively limited, once modelling focussed within two days or so. Just a few days ago this looked like a potential High Risk in the tornado department, but now looks to be mostly a significant wind-related, QLCS-generated threat, as opposed to an event with widespread discrete activity.
 

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