Here’s the news – La Niña, that cool pool of water in the Tropical Pacific, is back.
It’s baaaack! La Niña has returned to the Pacific. Source: NOAA
Here’s the question: Is that good or bad news?
Here’s the answer: It’s good news for the East Coast and not for Texas. It’s great news for a mellow autumn and rough news for mid-winter cold. It’s good news for retailers and ski resorts, it’s bad news for Christmas air travel. In short, it is a mixed bag of weather.
In the second week of September, the water in the Tropical Pacific became 0.9˚F (0.5˚C) colder than normal. This was low enough that the US weather service officially announced that a new La Niña had begun. Over a million square miles of ocean water were cooling the air above it, making the air dry and cold. This changed the air pressure, which changes wind patterns and weather. When such a huge amount of air is changed, it changes weather all around the globe.
Some of the weather changes were great. In general, La Niñas produce warmer and drier autumns, allowing some of those Midwestern crops that were planted late during the spring floods enough time to ripen. This will help the price of food. Unfortunately, the La Nina will also dry conditions in Texas, which could really use some rain.
La Niña also tend to shift the wind and air pressure patterns that steer Atlantic hurricanes. Since the event began in September, hurricanes have been shooting up the Atlantic Ocean, rather than skimming the East Coast, like Hurricane Irene. Storms in the Caribbean have gone due east rather than veering north into the Gulf Coast, like Tropical Storm Lee.
La Niñas frequently create global wind patterns that tend to steer Atlantic hurricanes away from US shores. Source: NOAA
La Niñas also tend to better the odds for cool, snowy mid-winters. This may make Christmas air traffic a mess, but it is the answer to skier’s prayers. This tends to increase midwinter clothing sales, a gift to retailers. And it provides a pretty, white Christmas.
Just remember this Christmas, as you watch the snowflakes fall—it all started with some cool water in the middle of the vast Pacific.
Evelyn Browning Garriss, historical climatologist, is a longtime writer for The Old Farmer's Almanac. She is also editor of The Browning World Climate Bulletin  and has advised farmers, businesses, and investors worldwide on upcoming climate events and their economic and social impact for the past 21 years.