Weather Folklore: Do big weather events come in 7 year cycles?

WSAV NOW Weather

SAVANNAH, Ga. (WSAV) — Weather is cyclonic – swirling areas of high and low pressure systems bringing tropical cyclones, tornadoes, thunderstorms, coastal flooding, ice and snow storms, and even excessive heat all around the globe.

Weather patterns do change. We see this every day but usual longer, decadal changes are caused by ocean & atmospheric interactions. One of the more well-known cycles is called ENSO (AKA El Niño-Southern Oscillation).

There are two phases of ENSO: El Niño, the warm phase, or La Niña, the cold phase. We talk about this cycle during hurricane season with how El Niños or La Niñas can affect tropical systems.

South Carolina Emergency Officials had a news conference last week over winter weather preparedness. They mentioned that while severe winter weather is rare here, it does happen like the ice storm of 2014. This 7 year old example made me think of the weather folklore – weather comes in 7 year cycles.

ENSO events occur every 3-7 years in the Pacific Ocean with either El Niño or La Niña lasting up to 1 year. This is where the 7 year cycle folklore comes from. Each event brings a change in weather patterns.

El Niño VS La Niña

Normally in the Pacific Ocean, trade winds along the equator blow east to west, bringing warm water towards Asia with up-welling of cold water to replace the missing warm water near South America. El Niño and La Niña patterns try to change this normalcy and end up changing global weather patterns.

As an El Niño develops, trade winds weaken. This allows warm water to instead to be brought back east. In a La Niña pattern, stronger than normal easterly trade winds are able to push even more warm water towards Asia. This leads to a stronger up-welling of colder, deeper ocean water brought to the surface.

Warm water near the equator influences not only where the jet stream sits but also the weather patterns it drives. During an El Niño, warm waters allows the Jet Stream to move further south, causing the southeast to be wetter and cooler than usual.

During an La Niña pattern, cold waters push the Jet Stream more north, causing the south to be warmer abd drier than normal. It can cause a more severe hurricane season.

Currently, La Niña conditions have developed in the Pacific Ocean according to the National Oceanic and Atmospheric Administration.

7-Year Weather Cycles: 2021-2008

Now let’s test to see if the 7 year cycle myth is true. I looked back from 2021-2008 to see if there would be any correlations for winter storms, excessive heat, coastal flooding, and severe weather over a 3-7 year stretch and then compared it to a possible El Niño and La Niña pattern at the time.

From 2008 to 2021, there have been only 2 instances of a 7-year weather pattern occurring. Around the 4th of July earlier this year, we were dealing with Tropical Storm Elsa. 7 years earlier in 2014, we were tracking Hurricane Arthur around the same time. The other instance was the 2018 and 2011 winter storm events, both happening in early January.

Most repeat events happen every 3-4 years with the exception of spring severe storms occurring almost every April.

EVENTDATEPATTERN
Winter StormJanuary 3, 2018La Niña
Winter StormFebruary 11-13, 2014Neutral
Winter StormJanuary 28-29, 2014Neutral
Winter StormJanuary 10, 2011Major La Niña
Winter StormFebruary 12-13, 2010El Niño
Excessive HeatMay 25-31, 2019Neutral
Excessive HeatAugust 2016Neutral
Excessive HeatJuly – August 2010Early La Niña
Coastal FloodingNovember 3-11, 2021Early La Niña
Coastal FloodingDecember 22-24, 2019Neutral
Coastal FloodingNovember 28, 2018Early El Niño
Coastal FloodingSept 25 – Oct 7, 2015Strengthening El Niño
Severe Wx / Heavy RainApril 23, 2020Neutral
Severe Wx / Heavy RainApril 19, 2020Neutral
Severe Wx / TornadoesApril 13, 2020Neutral
Heavy RainJune 10-12, 2019Neutral
Severe WxApril 19, 2019El Niño
Severe ThunderstormsApril 3, 2017Neutral
Severe ThunderstormsJune 17, 2016Neutral
Severe ThunderstormsApril 25, 2015Early El Niño
Severe ThunderstormsApril 19, 2015Early El Niño

El Niño and La Niña cycles drive larger scale weather patterns. It does have some influence on our day to day weather, but we see more of their influence with cooler or warmer temperatures and wetter or dry patterns over a longer period of time.

Hurricane season storms flourish when we are under a La Niña as this pattern leads to weaker wind shear and less atmospheric stability. The record-breaking 2020 hurricane season started out under neutral conditions but as we saw last year, storms quickly amplified as La Niña conditions became stronger through the end of the season.

While swirling areas of high and low pressure drive different weather patterns across the Coastal Empire and Lowcountry, weather is still be unpredictable weeks to years in advance. With winter storms occurring here every 3-4 years with under a La Niña set up, does this mean we are due for one soon? I guess we will just have to wait and see.

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