Pineapple Express

Chugga chugga chugga chugga choo choo! just kidding. This pineapple express has nothing to do with the movie nor the beloved children’s book titled The Pineapple Express. In fact, it this pineapple express refers to a weather phenomena that happens nearly 3,000 miles away on the western coast of North America, specifically, California.

For those living on the West Coast, and for those following the weather in that region, they may notice a massive increase in the amount of precipitation occurring over the next few days. The cause? The result of something called an atmospheric river. An atmospheric river functions much like a river does on land. It brings a great deal of moisture from one region to another. In the atmosphere, this is often done thanks to the jet stream in the upper air, along with some lower level system.

Figure 1: The surface chart valid for December 1st, 2012


As shown in Figure 1, the low pressure system sitting off of the coast of Washington provides the support to move the moisture shown in green in towards California and Oregon. In this particular case, since the moisture is taken from the Hawaiian Islands, it has been dubbed, “The Pineapple Express.”

Events like this can least several days and bring a lot of precipitation to the region in addition to higher winds. Certain parts of the region have been forecasted to receive over ten inches of precipitation and winds over 100 miles per hour as they approach the mountains. These events are important though as a large percentage of the annual rain fall for the region can be made up of just one Pineapple Express stopping by to say hello.

-by Timm Uhlmann

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