An explosive grenade is nicknamed a pineapple. A recent storm that clobbered California is nicknamed the Pineapple Express and it has been just as explosive.
The innocent sounding name comes from the type of wind that lofts up from the tropics to the West Coast. In the day of sailing vessels, it helped speed the voyage from Hawaii to Seattle, thus the name Pineapple Express. Of course, sometimes when the warm moist air hit the cool continental land mass, it would precipitate out in heavy rains, but Seattle was used to rains.
December’s Express was more than a Northwest drizzle. The Pacific Ocean was in the middle of a strong La Niña. This meant the Tropical Pacific and waters off the American coastlines were cooler than normal. Meanwhile the Western Pacific was unusually warm. West Pacific tropical disturbances were stronger and they could travel further north and east. When they neared North America, they hit the winter-cooled land and created a deluge.
Then the unexpected happened. The Arctic Oscillation has been strongly negative and has pushed a lot of US weather patterns further south than usual. (Just ask frozen Florida!) The Pineapple Express that normally sails happily to Seattle instead was steered south where it hosed down California.
This photo, taken by NASA satellite, shows the "pineapple express" storm that brought heavy rain to Southern California.
The results were stunning. For over a week California was hit by record-breaking storm after storm. Hillsides were hit with between 12 – 24 inches of rain, while one mountain sensor, Pascoes snotel, reported 17 feet of snow. From California, through Nevada, Utah, Colorado and Wyoming, regions reported up to 800% of their normal precipitation in that period. (See chart below. Credit: NOAA)
There were floods, landslides and avalanches, but not all results were bad. Reservoirs have been filled, Western snow packs are restored and California’s drought has nearly ended. Northern California is even reporting a resurgence in the number of returning salmon.
Most experts expect the Express to return to its normal Northwest route and California to return its normal dry La Niña weather. But it has been a pretty spectacular explosion for a wandering pineapple.
Have you ever "ridden" the Pineapple Express? Do we have any California fans? If you'd like to share your thoughts, I'd love to hear from you. (Just post comment below.)
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.