ST. LOUIS, Mo. – It may be hard to believe, but changes in water temperatures half a world away can have a major impact on weather patterns here in St. Louis. But, that is why we have been keeping a close eye on the central and eastern Pacific Ocean for the past several months.
Normally, the trade winds blow from east to west and cause warm surface water near the equator to stretch out from Central America all the way across the Pacific. However, in some years those trade winds get stronger and that forces the warm water all the way out into the western Pacific. This creates a vacuum that pulls much colder water from deep down in the eastern Pacific up to the surface – a process called upwelling.
This pattern of colder than normal water in the eastern pacific is called La Nina. The La Nina pattern forces the jet stream much further to the north than normal. This can lead to above normal temperatures across much of the southern United States with big time cold focused more into western Canada, the Pacific Northwest and into the Northern Plains.
As for precipitation, the south can tumble into drought while above normal precipitation impacts the Pacific Northwest and a small portion of the Ohio Valley with St. Louis hanging right on the edge.
In St. Louis La Nina years tend to be highly variable. No two are exactly alike. They can be warm or cold. They can range from dry to somewhat wet. On average snowfall is pretty close to normal with 20-25 inches in most La Nina winters. We can even get a couple of severe thunderstorm events during a La Nina. This is 2020 so maybe we should be ready for anything and everything!