May 29th, 2019 by Roy W. Spencer, Ph. D.
by Roy W. Spencer, Ph. D.
I had an op-ed published at Foxnews.com yesterday describing the reason why we have had so many tornadoes this year. The answer is the continuing cold weather stretching from Michigan through Colorado to California. A persistent cold air mass situated north and west of the usual placement of warm and humid Gulf air in the East is what is required for rotating thunderstorms to be embedded in a strong wind shear environment.
The temperature departures from normal so far this month show evidence of this cold:
In fact, in terms of departures from normal, so far this year the Northern Plains has been the “coldest place on Earth”, averaging 5-10 deg. F below normal:
The strong wind shear and warm advection provided at the “tightened” boundary between the warm and cold air masses is the usual missing ingredient in tornado formation, unlike Alexandria Ocasio-Cortez’s claim that a New Jersey tornado warning was somehow tied to global warming.
As has been pointed out elsewhere, a trend line fit to the number of strong to violent U.S. tornadoes has gone down from 60 in 1954 to 30 in 2018. In other words, the number of most damaging tornadoes has, on average, been cut in half since U.S. statistics started to be compiled:
Or, phrased another way, the last half of the 65-year U.S. tornado record had 40% fewer strong to violent tornadoes than the first half.
To claim that global warming is causing more tornadoes is worse than speculative; it is directly opposite to the clear observational evidence.