Fire Hose in the Pacific

The MJO, Madden Julian Oscillation, is a harmless looking little pool of wind and water drifting in the Tropical Pacific. It doesn’t look like anything special. But look out! It can shape hurricanes and droughts, floods and blizzards.

Currently California is being blasted by storm after storm. A powerful jet stream is carrying the tropical moisture from Hawaii to the West Coast, thus the name Pineapple Express. The direction of the jet stream and the blast of moisture is no surprise, however. It occurs every time that the MJO shifts into position.

The Pineapple Express not only drowns the West Coast, it shapes weather further east.

The MJO has two patterns: wet and dry. The wet types are areas where tropical winds are unusually quiet and the ocean surface is still, soaking up sunshine. It becomes unusually warm and heats the air above it. Moist air holds more water and as the hot air rises, it creates heavy rainfall. Winds blow out from the equator to the poles so a wet pool of rain stretches out from the MJO. As it drifts to the east, the MJO finally is south of the Hawaiian Islands. The Pacific jetstream catches the plume of moisture and carries it northeast. When the hot, wet air hits the cooler land, the tropical moisture pours itself out in a series of flooding rains. In the mountains, the Pineapple Express creates blizzards and avalanches.

The Pineapple Express causes floods and blizzards in the Western US and Canada. SOURCE − Walter Siegmund

The results can create weather on the West Coast as damaging as a hurricane on the East Coast. It is like a high-pressure fire hose blasting the coast with water. Like a loose hose on your lawn, it whips around, now blasting Seattle, next hitting San Francisco.

However, the impact is not limited to the West Coast. There is a lot of pressure in that stream of moisture as it blasts eastward. The jet stream carries weather patterns northeast. Moisture blasts the Northern Rockies and Canada’s Prairies. Unfortunately, the moisture is blasted away from the Midwest. Most of our Northern Plains are left high and dry and the jetstream normally doesn’t re-enter the US until the Great Lakes.

The Pineapple Express not only drowns the West Coast, it shapes weather further east.

The good news is that the impact of these rains will linger. Western reservoirs will refill. The snowpack will build and, the springtime melt will feed rivers from the Sacramento to the Missouri.

The first blog I ever wrote for the Old Farmer’s Almanac was about the Pineapple Express, so I will end this blog as I did that one.

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.)