La Niña can boost this year’s tornado season, just as it did with a deadly effect in 2011

La Niña can boost this year’s tornado season, just as it did with a deadly effect in 2011

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The past few months have seen the strongest La Niña signal since the winter of 2010-2011. So the question is whether this spring continues to mirror that year, which turned out to be the most expensive ever recorded for tornadoes and the deadliest in nearly 100 years.

“The harsh weather season is actually a collection of several short weather events, and anticipating individual events over long delivery times is often tricky,” Sam Lillo, an atmospheric researcher at the University of Colorado at Boulder, told CNN.

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

The most deadly tornado season in modern history

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

Almost all deaths in 2011 occurred during the extremely active months of April and May. In April alone he saw 875 confirmed tornadoes, more than any registered month. The Super Outbreak on April 27 registered 226 tornadoes, the largest number of tornadoes ever seen in a single day, including destructive tornadoes in Birmingham and Tuscaloosa, Alabama.
Volunteers search homes destroyed on April 30, 2011 in Tuscaloosa, Alabama.
Just a few weeks later, Joplin, Missouri, was hit by a large 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 almost $ 3 billion in direct damage.

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

While localized and small-scale weather features played a role in shaping these tragic days, it is worth examining the general large-scale patterns that fueled the historic 2011 tornado season to determine the risk of similar days this year.

“Every year has some potential (of 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 make sure people are prepared and have a plan, “Bunting said.

A person examines the damage the day after a tornado hit Joplin, Missouri, killing dozens on May 23, 2011.

Active forecast for this spring

To paint a picture of what the weather in the coming weeks to months might look like, meteorologists look at La Niña and other global climates and weather patterns, such as the Arctic Oscillation (which is different from the polar vortex), to create what are called sub-seasonal forecasts.
Lillo runs one of those models that “focuses on the slow and predictable parts of the atmosphere” to create forecasts several weeks in advance. Forecasting models like this are important for things like seasonal temperature forecasts, which are used in energy trading markets, and hurricane season forecasts released each year by the National Oceanic and Atmospheric Administration (NOAA).

Lillo’s model recently predicted – a month in advance – the outbreak in the Arctic that hit the center of the United States in February. Now, the focus shifts to what these long-term patterns can reveal as we move into the spring-heavy storm season.

“In general, forecasts are showing furrows with above normal temperatures in the south, cooler in the north and this temperature gradient increasing the jet stream in the center of the United States,” said Lillo. (The jet stream is the main storm path in the mid-latitudes of the northern hemisphere and divides the coldest air in the north and the warmest air in the south.)

During La Niña, stronger temperature differences tend to develop between hot and humid air in the southern United States and cooler, drier air in the north. This sets up a faster jet stream that can cause severe weather outbreaks.

“The fastest jet has all the potential for stronger storm systems and harsh weather,” said Lillo.

In March, the southern United States is historically the area where severe storms, including tornadoes, are most likely. Then, as the northern hemisphere begins to warm up, the tornadoes’ target will shift westward to the center of the United States and eventually northward to the northern plains in the summer.

“The pattern of the jet is not unfavorable for severe weather, as we arrived a little later in March and certainly later,” said Bunting. “If this pattern continues, very strong wind fields along the Gulf Coast close to the hot and humid air suggest that the Gulf Coast in the short term could be an area to be closely watched.”

How La Niña relates to tornadoes

Similar to this year, a moderate La Niña was the main feature in 2011. La Niña, and its counterpart, El Niño, can play a significant role in the position of jet flow, temperature and precipitation patterns over the US, which all play a role in the formation of severe weather.

El Niño or La Niña conditions in the winter months can be used to help identify the frequency of tornadoes during the peak of the strong spring storm season, recent studies have found.

“The flow of hot, humid air from the Gulf of Mexico increases in strength during the springs that follow La Niña, which produces the fuel needed to form storms,” ​​said Jason Furtado, assistant professor of meteorology at the University of Oklahoma.

“The stronger flow increases the shear of the low-level wind, which also favors the formation of tornadoes and hail storms.”

The past few months have seen the strongest La Niña since 2011, and it is expected that this pattern will continue to impact the climate in the coming months, in the middle of the severe weather season, according to the NOAA Climate Forecast Center.

The time to prepare is now

Although strong storms occur throughout the year in the United States, the peak occurrence of strong storms is during the spring weather, which includes March, April and May.

So far this year, there have only been 27 reports of tornadoes, which is well below normal. In the past 15 years, the United States has recorded an average of about 130 tornado reports in the first days of March.

But it is not just the reports of tornadoes that have declined. Reports of hail and damaging wind are also below average this year.

“There were many seasons that started off smoothly and did just the opposite,” said Bunting.

2011 also started below average for tornado and hail reports for much of March, according to data compiled by the SPC, before accelerating rapidly through the rest of spring.

The next forecast depends on where the jet stream will stop in the coming weeks.

Now is the time to review your plans for the harsh climate. Know where to find your daily local forecast. Get multiple ways to get storm and tornado alerts and warnings: via wireless emergency alerts, NOAA Weather Radio, local news stations and more. And know where to take shelter at home, at work or at school in the event of a tornado.

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

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