La Niña, such as the one now occurring, is considered to be conducive to wind shear, a known factor in tornado conditions – as mentioned below.
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On the night of Dec. 10–11, 2021, an outbreak of powerful tornadoes tore through parts of Arkansas, Mississippi, Missouri, Kentucky, Tennessee and Illinois, killing dozens of people and leaving wreckage over hundreds of miles, says The Conversation (via Phys.org).
Hazard climatologists Alisa Hass and Kelsey Ellis explain the conditions that generated this event—including what may be the first “quad-state tornado” in the U.S.—and why the Southeast is vulnerable to these disasters year-round, especially at night.
What factors came together to cause such a huge outbreak?
On Dec. 10, a powerful storm system approached the central U.S. from the west. While the system brought heavy snow and slick conditions to the colder West and northern Midwest, the South was enjoying near-record breaking warmth, courtesy of warm, moist air flowing north from the Gulf of Mexico.
The storm system ushered in cold, dense air to the region, which interacted with the warm air, creating unstable atmospheric conditions.
When warm and cold air masses collide, less dense warm air rises upward into cooler levels of the atmosphere. As this warm air cools, the moisture that it contains condenses into clouds and can form storms.
When this instability combines with significant wind shear—winds shifting in direction and speed at different heights in the atmosphere—it can create an ideal setup for strong rotating storms to occur.
On a tornado ranking scale, how intense was this event?
At least 38 tornadoes have been reported in six states during this outbreak, causing widespread power outages, damage and fatalities.
The National Weather Service rates tornadoes based on the intensity of damage using 28 damage indicators from the Enhanced Fujita, or EF, scale. Storm assessments and tornado ratings can take several days or longer to complete.
As of Dec. 12, at least four EF-3 and five EF-2 tornadoes have been confirmed. EF-2 and EF-3 tornadoes are considered strong, with wind speeds of 113–157 mph and 158–206 mph respectively.
Continued here.
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[…] Why the southern US is prone to December tornadoes […]
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Tornadic storms in the Southeast are often powered by an abundance of wind shear. They do not rely as heavily on rising warm, humid air that creates atmospheric instability—conditions that require daytime heating of the earth’s surface and are more prevalent in the spring.
Forecasting for this event was accurate and predicted a major outbreak several days in advance.
This has been rushed out, by the look of it (‘Not peer reviewed yet’).
But why would warming, if it goes on, mean more La Niñas (which bring cooling to parts of the Pacific) that help to provide tornado-favourable wind shear conditions?
DECEMBER 14, 2021
Study: Winter tornadoes to get more powerful as world warms
Nasty winter tornadoes—like the deadly ones last week that hit five states—are likely to be stronger and stay on the ground longer with a wider swath of destruction in a warming world, a new study shows.
The combination of a longer and wider track with slightly stronger winds means some rare winter tornadoes that are killers now will have nine times more the power by the end of the century if carbon dioxide levels continued to rise, according to a study presented at the American Geophysical Union conference Monday.
The study, which pre-dates the devastating Mayfield, Kentucky, tornado outbreak, looks at strength and not frequency of big tornadoes as climate change progresses. Not peer reviewed yet, it was presented in poster form as a peek at new research to be published later.
https://phys.org/news/2021-12-winter-tornadoes-powerful-world.html
‘nine times more the power by the end of the century if carbon dioxide levels continued to rise’ – sounds absurd.
Trapp took the conditions during two large tornado strikes in 2013—the Hattiesburg, Mississippi, tornado that in February of that year injured 82 people with winds of 170 mph and the Moore, Oklahoma, tornado that killed 24 people with winds up to 210 mph (340 kph) in May— and put them into dozens of computer simulations of worst-case climate change scenario by 2100, which other scientists say is increasingly unlikely.
There’s your problem, or one of them – silly computer games using far-fetched scenarios. Hardly a ‘study’.
hold of their folks, I got the 411 the other night about these tornadoes and storms. Presidunce Xiden has looked at his tea leaves and the entrails of goats and determined – global warming did it!
Well there ya have it. Now we can shut down all those expensive research studies and such and move onto saving the world from CAGW. Or something.