We’re expecting a storm, and its source will be an atmospheric river, or AR, which is exactly what it sounds like: a river flowing through the atmosphere. There are several, and they transport most of the water vapor outside of the tropics. River is the correct word, though maybe, Large River would be more appropriate. They average 300 miles wide and their flow by volume is similar to that at the mouth of the Mississippi.

AR is the correct term, but I am going to use sky river, which makes other rivers I have known land rivers.

A third to a half of West Coast rain comes from sky rivers, though usually not in April, which is one of our dryer months. That is, the ditty April showers bring May flowers did not originate here. We have flowers all year long, too.

Like the Mississippi, sky rivers meander, though in general they flow from the topics to the poles, just as land rivers flow from high ground to lower ground overall. Humans haven’t figured out a way to force sky rivers into fixed channels, so they wander freely.

The sky river arriving tomorrow is streaming directly from Hawaii to California, and is known as the Pineapple Express.

When a sky river wanders over land, it may release some of its water as rain or snow, or it may not. How much precipitation we will get, as well as its location and form, are still topics of speculation 24 hours before the event. Residents are advised to monitor forecasts during the next three days, as mudslide-creating  rain levels are one possibility.

Scientists have a lot to learn about global atmospheric phenomena, including sky rivers. We are still learning why some land rivers meander as well, and finding out that there are consequences to constraining them, including reduced biodiversity. Are there sky river creatures?  I hope so.

Do airplanes have to ford sky rivers?