TULSA, Okla. (KTUL) — It's weird to think that cooler than average water temperatures off the coast of Peru mean warmer than average temperatures in Oklahoma. Yet that's what NOAA said when they announced that La Nina was likely for this fall and winter.
La Nina is a multi-year climate shift where waters off the coast of western South America are temporarily colder than normal and water temperatures around SE Asia are significantly warmer than normal. It's known to impact weather phenomena around the world.
For the US, most typically we see cooler and wetter conditions across the northern states, and warmer and drier conditions for the southern states, including Oklahoma.
Meteorologist and Climate Specialist Nicole McGavock from the National Weather Service says the reason we see those conditions is due to how the warmer waters from SE Asia impact the polar jet stream.
"The air with those thunderstorms near the equator goes up, and when it hits the troposphere it splits going north and south," said McGavock. "As that air moves towards the poles, it begins to cool and sink. Where that air sink is where we find the jet stream."
The jet stream is a river of fast-moving air that circles the planet. In the northern hemisphere, it typically shifts south during the winter bringing more rain, storms, and sometimes snow to places like Oklahoma. A La Niña weather pattern tends to push the jet stream farther north keeping the storms away from the southern US.
This doesn't mean that Oklahoma will go without snow or cold this year. One overarching rule of weather is there are always exceptions.
"What El Niño and La Niña do is kind of tip the scales one way or another," said McGavock. "But there are a lot of other influences that impact what we see on a day to day basis and over a winter season."
Looking at historical La Niña events, data shows that while most of them tended to be drier, there were a few that were significantly wetter. For snow lovers, while La Niña winters tend to be warmer, they conversely tend to have more small snow events. "Small" though, is the keyword.
"We find that we actually see more days with flurries or a dusting of snow during La Niña winters," said McGavock. "What we don't see is a correlation between La Niña and snowfalls with more than half-an-inch."
NOAA studies also point to an uptick in severe weather during the springtime after a La Niña winter, but even that isn't set in stone. Some years like spring of 2011 were big for severe weather in Green Country and the end of a two year La Niña phase. 2007 was also a La Niña year but it was only an average year for severe weather.