Is El Niño to Blame For These Winter Tornadoes?

We've seen more tornadoes than average in the U.S. so far this winter. You may be tempted to blame El Niño for this. But does even one of the strongest El Niños on record actually have anything to do with the more tornadic winter?

Several Notable Severe Events Since November

First, there's been a number of notable severe weather events since the beginning of November, including:

• A Veterans' Day derecho spawned over a dozen tornadoes, primarily in Iowa.
• The following week, roughly 30 tornadoes touched down in the High Plains, including an EF3 tornado near Liberal, Kansas, that was the strongest on record so far west so late in the season. 
• Christmas week, an estimated 55 tornadoes tore through a dozen states from Texas to West Virginia and North Carolina. EF4 tornadoes hit Holly Springs, Mississippi, and Garland, Texas. At least one tornado was reported in the U.S. for a record-tying six straight December days.
• A killer tornado struck Duette, Florida, on Jan. 17.
• At least 10 tornadoes struck the Deep South on Groundhog Day, including an EF2 tornado near Scooba, Mississippi, and an EF1 at Fort Stewart, Georgia.
• Roughly two dozen tornadoes, including an EF3 tornado near Century, Florida, touched down over the South on Presidents' Day.
• Just one week later, over a dozen tornadoes carved through parts of the Deep South, including Pensacaola, Florida.

According to Dr. Greg Forbes,  severe weather expert for The Weather Channel, a preliminary total of 235 tornadoes occurred in the U.S. from November 2015 through early morning, Feb. 24, 2016.

This count is almost 57 percent higher than the 20-year average count through that same time period of 150 tornadoes, according to Forbes.

Breaking the totals down by month, only January was less tornadic than average in the U.S.

All this has happened during what has been a record-tying strong El Niño, so surely El Niño is the cause, right? 

Well, in the words of the late Leslie Nielsen playing in the classic 1980 comedy, Airplane, "Don't call me Shirley."

El Niño-Tornado Connection: Hazy, At Best

El Niño does not, by itself, spawn tornadoes or tornado outbreaks.

El Niño is the periodic warming of the central and eastern equatorial Pacific water that exhibits a forcing on the overall atmospheric pattern, particularly in the winter months.

One thing common to strong El Niños is a more bullish southern-branch, or subtropical jet stream. 

While this subtropical jet stream typically camps, at times, over parts of the southern U.S. each winter, in a strong El Niño, it is most anomalously strong farther south, from the eastern Pacific Ocean through Mexico, into the Gulf of Mexico, then into the Florida Peninsula.

This tends to pull the track of winter frontal systems closer to the Gulf Coast and Florida. Coupled with a stronger southern-branch jet stream, severe thunderstorms can be more numerous in parts of the South. 

Numerous studies since the 1990s have examined the potential link between El Niño and tornadoes, not simply in the winter, but also in the more active spring and summer months.

(MORE: Weakening El Niño -> More Dangerous Hurricane Season)

Forbes says year-to-year tornado statistics can be skewed by either the occurrence or lack of one or more large outbreaks. "These are due to strong transient weather systems (such as strong jet-stream streaks and their associated strong frontal systems), relatively independent of such large-scale influences (as El Niño)."

Essentially, tornadoes, and tornado outbreaks occur at a much smaller scale than the huge scale of an El Niño. Tornadoes are notoriously fickle, forming on some days with a favorable overall environment for severe weather, but not on others. El Niño simply doesn't operate on that small a scale to determine whether you'll simply have an area of thunderstorms with flooding rain, or a tornado outbreak. 

Basically, even a record-tying El Niño is not the only "driver" of the atmospheric pattern at any given time.

(MORE: El Niño's Facts and Myths)

One other monkey wrench that clouds any possible trends in tornadoes during El Niños is "tornado inflation", the overall increase in observed weaker (EF0 or EF1) tornadoes over the past several decades due to more widespread spotter networks, advancements in technology (Doppler radar, smartphones, social media), and population increase.

There are, however, at least a few tendencies of note from previous studies.

For example, of the 27 largest, most impactful tornado outbreaks in U.S. history, twice as many January-through-April outbreaks occurred during La Niña (6) as did El Niño (3), according to Dr. Forbes' research.

From May through December, however, 9 such outbreaks occurred during an El Niño, compared to just 2 during a La Niña and another 5 during a neutral season.

A recent study by the National Weather Service in Tallahassee, Florida, found that about double the number of tornadoes can be expected in an El Niño from November through April in central and South Florida compared to a La Niña or neutral season.

Similarly, Dr. Forbes examined 13 previous moderate to strong El Niños and La Niñas, and found 8-9 more November through April tornadoes had occurred in the Sunshine State during each of the 13 El Niño seasons examined than during the La Niña seasons.

Most infamously, Florida's deadliest tornado outbreak occurred during the previous strong El Niño. On Feb. 22-23, 1998, 42 were killed and over 3,000 buildings were damaged or destroyed during a central Florida tornado outbreak, which included a trio of F3 killer tornadoes in the Orlando metro area.

(MORE: 10 Worst Tornadoes of 2015)

Previous studies by Joe Schaefe, former head of the Storm Prediction Center, and others have noted at least a weak correlation with stronger winter and early-spring Florida peninsula tornadoes (EF2+) and El Niños. 

The bottom line is both El Niño and La Niña may have some influence on the occurrence of tornadoes, but it's difficult to separate the many other smaller and large-scale factors in play.

MORE ON WEATHER.COM: South Tornado Outbreak (Feb. 23-24, 2016)