Climate Denial Crock of the Week

Washington Post:

Water temperatures in the Gulf of Mexico often enter the conversation during hurricane season, but they also play a role in tornado season each spring. Concern is growing for the potential impact that abnormally warm sea surface temperatures will have in the weeks and months ahead, with experts warily keeping tabs on what could be a busy tornado season.

Friday’s tornado outbreak in Mississippi and Alabama, which killed at least 24 people, coincided with gulf waters up to several degrees warmer than normal and as high as the upper 70s.

April, May and June are historically the most active for severe weather and tornadoes, with an average of 660 twisters spinning up within the three-month window. They materialize seemingly like clockwork, creeping north across the Deep South before swimming over the Plains and the nation’s heartland.

While considerable variability can occur year to year, there may be ties between gulf sea surface temperatures and the frequency and intensity of severe weather events in the U.S. Deep South in particular.

In the months ahead, several key atmospheric processes could favor a busier-than-normal tornado season, including the warm gulf water, but the jury is still out on just how active it will be. Seasonal tornado forecasting is still in its infancy, and meteorologists are careful to remind the public that confidence remains low in what lies ahead.

The year has already been off to a historically active start, with a preliminary total of 168 tornadoes touching down across the Lower 48 states in January. That’s the second-most on record. In February, there were 55 tornadoes — double the average of 29. 

Oklahoma reported 17 tornadoes in January and February. The average during that window is one.

On Jan. 16, two tornadoes spun up in eastern Iowa, the state’s first January tornadoes in 50 years.

Alabama also logged 29 tornadoes during January, smashing state records, and New Jersey even faced an EF2 tornado, on the 0-to-5 scale for twister intensity, on Feb. 21. That marked the Garden State’s first February twister in nearly a quarter-century.

Warm Gulf of Mexico water temperatures probably boosted the winter activity, consistently running several degrees above average. In addition, temperatures were exceptionally high over land, especially in the eastern United States. January was 5.1 degrees above normal in the Lower 48. February was 2.7 degrees above average.

March tornado activity had been quiet until Friday’s outbreak in the South, which may have kick-started the spring season.

Tornadoes require two simple ingredients: fuel and spin. Enough fuel for storms — known as convective available potential energy or CAPE — must be present to build thunderstorms and brew storm clouds. CAPE is generated by warm and humid air. Changing winds with altitude, known as wind shear, can help those clouds to rotate.

Both ingredients need to overlap to yield a tornado threat. Without shear, thunderstorms tend to take the form of disorganized clusters, squall lines or clumps. That reduces the tornado threat. Too much shear, however, and a thunderstorm can be torn apart before it can mature and deliver a tornado.

During the winter, shear abounds — it’s largely ever-present thanks to the jet stream, which lurks over the United States throughout the cold season. But CAPE supplied is usually limited in the winter because of the lack of heat and humidity. During summer, CAPE is plentiful as it heats up, but shear is often lacking as the jet stream retreats. Spring marks the juxtaposition of both.

Below, following the unprecedented DeRecho and tornado outbreak of December 2021, I spoke to a number of experts who outlined how a warming climate favors stronger storms both earlier, and later in the season than we have traditionally seen.