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Oscillation Effects on Tornado Seasons

Will La Niña Trigger a Dangerous Spring Severe Weather Season? | The  Weather Channel - Articles from The Weather Channel |
Low level moisture flow with El Nino and La Nina (Source:

When it comes to El Nino and La Nina, they can usually play a role in the way tornado seasons play out in the United States.

El Nino’s Impacts on Tornado Season
El Nino usually leads to less tornadoes during the peak tornado season in the spring. This is due to El Nino weakening the surface winds which prevents warm, moist, unstable air from making it far as the Great Lakes. This leads to tornadoes only being concentrated over the Southern States with lesser tornadoes being possible in the Northern U.S. States.

La Nina’s Impacts on Tornado Season
La Nina can usually lead to an increase in tornado activity especially for the east half of the U.S. This is due to La Nina bringing moisture further north which can lead to tornado outbreaks happening as far north as the upper Great Plains and the Great Lakes. Unfortunately, this could mean the potential for possibly some devastating tornado outbreaks such as the 2011 Super Outbreak that brought 360 tornadoes within a span of 4 days in late April 2011. This lead to around 12 billion dollars in damages and the outbreak killed 321 people. Even more baffling, 4 EF5 tornadoes would touch down on one day during the outbreak.

Remembering the deadly Super Tornado Outbreak of 2011 | AccuWeather
Area that the Super Outbreak of 2011 affected. (Source: Accuweather)

Without El Nino and La Nina Impacts on Tornado Season
Without either oscillation, there is still the potential for a significant tornadoes.

Intensity of El Nino and La Nina
The intensity of El Nino and La Nina can also have an effect on how either oscillation plays out. For example, with a weak La Nina, this can lead to a gradual increase in tornado activity while moderate and greater leads to a sudden increase in tornado activity during the spring. With a weak El Nino, they typically mean a slow increase in tornado activity during the spring while a moderate to strong El Nino can lead to lesser activity compared to weak El Nino.

Overall tornado activity can often be correlated to how oscillations such as El Nino and La Nina. Even without the presence of both tornado activity can still be dictated due to the pattern.


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