La Niña could boost this year’s tornado season just as it was deadly in 2011

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In recent months, we have seen the strongest La Niña signal since the winter of 2010-2011. So the question is whether this spring continues to reflect that year, which was the most expensive ever for tornadoes and the deadliest in nearly 100 years.

“The severe weather season is actually a collection of different short-term weather events, and it’s usually tricky to anticipate individual events over long lead times,” Sam Lillo, an atmospheric researcher at the University of Colorado at Boulder, told CNN.

“What we can say instead is whether the chances of the ingredients coming together for these events are higher or lower than normal: this year it’s higher than normal.”

The deadliest tornado season in modern history

The remarkable 2011 tornado season was the deadliest in the modern era, with more than 550 fatalities – second only to a total of 794 tornado deaths in 1925.

Nearly all deaths in 2011 occurred during the extremely active months of April and May. In April alone, 875 were seen confirmed tornadoes, more than any month. The Super Outbreak on April 27 recorded 226 tornadoes, the most tornadoes ever seen in a single day, including destructive twisters in Birmingham and Tuscaloosa, Alabama.
Volunteers search destroyed homes on April 30, 2011 in Tuscaloosa, Alabama.
Just a few weeks later, Joplin, Missouri was hit by a first-class EF5 tornado that killed more than 160 people. It was the deadliest tornado in more than 60 years, as well as the most expensive tornado on record, with nearly $ 3 billion in direct damage.

“Looking back at 2011, it was the sheer magnitude of the number of events, the fact that affected so many populated areas and, of course, the unbelievably high toll in terms of deaths, injuries and dollar damage,” said Bill Bunting, chief. of forecast operations for the National Weather Service’s Storm Forecast Center (SPC).

While local and small-scale weather features played a role in setting up both tragic days, the general large-scale weather patterns that have brought in in the historic 2011 tornado season are worth looking at to determine the risk for similar days this year.

“Every year has some potential (from tornado outbreaks); it’s just a matter of trying to accurately predict, with as much lead time as possible, where that area is likely to be and then making sure people are prepared and have a plan , ‘Said Bunting.

A person investigates the damage one day after a tornado ripped through Joplin, Missouri, killing dozens on May 23, 2011.

Active forecast for this spring

To paint a picture of what the weather for the next few weeks to months might look like, forecasters look to La Niña and other global climate and weather patterns, such as the Arctic Oscillation (which is different from the polar vortex). construct what are so-called sub-season forecasts.
Lillo runs one of these models that “focuses on the slow, predictable parts of the atmosphere” to make forecasts several weeks in advance. Such forecasting models are important for things like seasonal temperature forecasts, which are used in the energy trading markets, and hurricane season forecasts published every year by the National Oceanic and Atmospheric Administration (NOAA).

Lillo’s model recently predicted – with a one-month turnaround time – the Arctic outbreak that gripped the central US in February. Now the focus is shifting to what these long-term patterns could reveal as we enter spring’s severe storm season.

“In general, the forecasts show ridges with above-average temperatures in the south, cooler in the north, and that temperature gradient that amplifies the jet stream through the middle of the US,” Lillo said. (The jet stream is the main storm path across the mid-latitudes of the Northern Hemisphere, distributing colder air to the north and warmer air to the south.)

During La Niña, stronger temperature differences develop between warm and humid air in the south of the US and cooler, drier air in the north. This allows for a faster jet stream that can cause severe weather outbreaks.

“The faster jet stream has all the potential for stronger storm systems and severe weather,” said Lillo.

In March, the southern United States has historically been the area where severe storms, including tornadoes, are more likely. Then, as the Northern Hemisphere starts to warm up, the rose for tornadoes will shift west to the central US in the summer and eventually north to the northern plains.

“The jet stream pattern is not unfavorable for severe weather as we come a little later in March and certainly beyond,” said Bunting. “If that pattern continues, very strong Gulf Coast wind fields in close proximity to warm, humid air suggest that the Gulf Coast may be an area to keep a close eye on in the short term.”

How La Niña relates to tornadoes

Like this year, a moderate La Niña was the main feature in 2011. La Niña, and its counterpart, El Niño, may play an important role in the position of the jet stream, temperature and precipitation patterns over the US, all of which play a role. in the formation of severe weather.

The El Niño or La Niña conditions in the winter months can be used to determine the tornado frequency during the peak of the severe storm season in the spring, recent studies show.

“The flow of warm, moist air from the Gulf of Mexico intensifies during the sources that track La Niña and produce the fuel needed to form storms,” ​​said Jason Furtado, assistant professor of meteorology at the University of Oklahoma.

“The stronger current increases the low wind shear, which also promotes the formation of tornadoes and hailstorms.”

Recent months have been the strongest La Niña since 2011, and this pattern is expected to continue to affect the weather in the months ahead, in the heart of the tough weather season, according to NOAA’s Climate Prediction Center.

It is now time to prepare

While severe storms occur in the US year-round, the peak time for severe storm outbreaks is during the meteorological spring, which includes March, April, and May.

This year there have been only 27 tornado reports so far, which is well below normal. Over the past 15 years, the US generated an average of about 130 tornado reports in the first days of March.

But it’s not just tornado reports that aren’t available. Reports of hail and damaging wind have also been below average so far this year.

“There have been many seasons that started off quietly and did the exact opposite,” said Bunting.

2011 also started below average for both tornado and hail reports for much of March, according to data collected by the SPC, before accelerating rapidly throughout the remainder of the spring.

The upcoming forecast depends on where the jet stream will end in the coming weeks.

Now is the time to rethink your bad weather plans. Know where to find your daily local weather forecast. Have multiple ways to get severe storm and tornado watches and alerts: via Wireless Emergency Alerts, NOAA Weather Radio, local news stations, and more. And know where to hide at home, at work or at school when a tornado strikes.

Advised Bunting: “This is the time of year when we need to start thinking a little more about the possibility of severe storms and develop that pre-event planning.”

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