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Let all the dreamers wake the nation: Another atmospheric river runs through Portland.
Your commute home Thursday night was wetter than usual and not just your imagination (or if you’re a night worker, here’s your heads-up). The National Weather Service has observed a series of frontal systems moving now through Wednesday that could by Monday be considered a flood hazard.
One- to two-thirds of an inch of rain is likely for Portland by tomorrow, while the coast could see between 1½ and 3 inches and the Cascades up to 4 inches of rain. Oregonians can handle rain, usually, but wind is another story. Friday could see winds between 20 and 30 miles per hour, so strap down your holiday lawn lights.
As one system fades Saturday, another will pass through on Sunday. The weekend will be a little dryer for the coast and mountains, but Portland could see between a quarter and a full inch of rain by Monday. The NWS recommends staying vigilant if you live in an area prone to flooding.
Monday is when we learn once again that moisture is the essence of wetness. It’s not the amount of rain that will be the problem, but how much water from atmospheric rivers gets into the actual rivers from Monday to Thursday. Add the threat of winds up to 30 to 40 miles an hour, and Santa might want to do more than keep his wind surfboard handy. The NWS notes that there is still much uncertainty around the fronts as they develop and move, but expect at least minor flooding at this stage.
If “atmospheric river” seems like a new phrase weather forecasters made up to sell weather, think again. The Christmas Flood of 1964 and the Willamette Valley Flood of 1996 were both caused by atmospheric rivers, so here’s hoping history doesn’t repeat itself. They can drop the rough equivalent of “the average flow of water at the mouth of the Mississippi River,” according to the NWS (which calculates this by determining “the mass of water vapor in the atmospheric river and divid[ing] by the density of liquid water,” if you want to know how they know that). They’re serious events, even for areas allergic to umbrellas.
