Volume 6, Number 7, April 2016
People are starting to ask: What impact will a large pool of cooler than normal water out in the middle of the equatorial Pacific Ocean have on this summer's weather in Alabama?
NOAA has issued a La Niña "watch" for the upcoming year, and sea surface temperatures in that part of the Pacific are already cooler than normal, after being warmer than normal during the just passed El Niño Pacific Ocean warming event.
We will most likely be in the transition between the two this summer, which history tells us means a slightly higher than normal chance of a summer than is warmer and drier than seasonal norms, especially in the southern two-thirds of the state.
"Slightly higher than normal" means that if most summers have a 50/50 shot at being warmer or cooler, a La Niña transition summer might have a 55 or 60 percent chance of being warmer and drier. We've had wetter and cooler La Niña summers in the past, but that's the way statistics sometimes work.
That slightly higher than normal chance of warmer and drier also extends into the winter during a La Niña year, especially the closer you are to the Gulf. La Niña pushes northern and Ohio Valley states toward cooler and wetter (brrrrr) winters. North Alabama is sort of in the pivot area between the two, so we can go either way or one and then the other. And then back. It's what makes our weather so ... interesting.
El Niño warming and La Niña cooling do these things, in part, by pushing around the jet stream over North America. El Niño tends to pull the jet stream further south, while La Niña tends to keep the jet stream more anchored in the north. But that's just a tendency, not a long range forecast.
June 1 is the start of the Atlantic hurricane season, and we are still in the longest major hurricane "drought" in U.S. history. Hurricane Wilma, in 2005, was the last major hurricane (category 3 or larger) to hit the U.S., so this drought is going on eleven years. The previous longest streak without a major hurricane was eight years.
We should note Atlantic hurricanes tend to be more frequent during La Niña years (not always, but more so than normal), so this might be a good time to make your severe weather plans for this summer and fall.
-- John Christy