In the whirlwind that is 2018, there has been a notable lack of high-end twisters.
We’re now days away from this becoming the first year in the modern record with no violent tornadoes touching down in the United States. Violent tornadoes are the strongest on a 0 to 5 scale, or those ranked EF4 or EF5.
It was a quiet year for tornadoes overall, with below normal numbers most months. Unless you’re a storm chaser, this is not bad news. The low tornado count is undoubtedly a big part of the reason the 10 tornado deaths in 2018 is also vying to be a record low.
While we still have several days to go in 2018, and some severe weather is likely across the South to close it out, odds favor the country making it the rest of the way without a violent tornado.
If and when that happens, it will be the first time since the modern record began in 1950.
2005 came close to reaching this mark. That year, the first violent tornado didn’t occur until Nov. 15, much later than typical for the first of the year, which tends to come in early spring.
This year’s goose-egg may seem to fit a recent pattern.
In simple terms, there have been down-trends in violent tornado numbers both across the entire modern period, and when looking at just the period since Doppler radar was fully implemented across the country in the mid-1990s. A 15-year average as high as 13.7 in the mid-1970s will drop to 5.9 next year.
Expanding to include all “intense” tornadoes, or those F/EF3+, this year’s 12 is also poised to set a record for the least.
Right now, the mark there is held by 1987 when there were 15 F3+ tornadoes. As with violent tornadoes, this grouping is also exhibiting both a short and long-term decrease in annual numbers, likely for similar reasons.
The causes for 2018′s lack of violent tornadoes are many, but one key factor is high pressure tending to be more dominant than normal throughout peak season this past spring. This was particularly so during April and May, when tornado numbers were below to well below normal.
Although the country ended up seeing a number of memorable tornado events after the spring, including several this fall, in most years over half of the tornadoes occur from March through May. Making up those numbers is difficult at other times of the year when ingredients for them are less likely.
Despite the downtrend in annual numbers, studies continue to find that more tornadoes are happening on fewer days. In that light, it is certainly possible this drought won’t last much longer.
HT/marcusn, SMC, Neo
via Watts Up With That?
December 27, 2018 at 08:02AM