El Niño Comes Alive
Sea surface temperatures really ramped up in the Tropical Pacific over the course of October, and it is looking increasingly likely that we’ll have a weak to moderate El Niño for the 2018–2019 winter. The Pacific Northwest is generally warmer and calmer than normal during El Niño years, with near or slightly below average precipitation, below average mountain snowfall, and a significantly reduced risk of widespread arctic outbreaks and lowland snow events.
During El Niño winters, the increase in sea-surface temperatures at the equator warms the air mass over the Tropical Pacific, which in turn enhances the strength of the Pacific jet stream by increasing the meridional temperature gradient over the mid-latitudes. However, this jet stream often splits into two off the West Coast, with one stream going into the Alaska Panhandle and another going into California, leaving the Pacific Northwest warmer and drier than normal. This El Niño is expected to be similar in strength to the 2002–2003 and 2009–2010 El Niños, both of which had this split flow pattern in spades and had above-average temperatures, below-average mountain snowpack, and slightly below-average precipitation over the region.
Of course, all El Niños stick to the script of warmer and calmer-than-normal weather. The extremely strong 2015–2016 El Niño gave Seattle its wettest winter on record, and Seattle’s snowiest winter occurred during the weak El Niño of 1968–1969. My mom still talks about her sled races down Clyde Hill in Bellevue during January 1969—I wish I were there!
The Blob Returns, but will it stick around?
Remember the “Blob” of warm water off our coast in 2014 and 2015 that made the 2014–2015 winter the mildest one on record for many locations around the Pacific Northwest? Well, recent satellite observations show yet another “blob” of warm water in the North Pacific that was formed by a large ridge of high-pressure there. This blob may quickly dissolve during November or December if a series of storms move over the North Pacific and mix the water column, but if a general ridging pattern remains, the blob will continue to increase in depth and extent and will help increase surface temperatures throughout the West Coast.
The Final Word
Given the El Niño in the Tropical Pacific and the large area of warm water in the North Pacific, above-average temperatures look likely, with precipitation probably near or slightly below normal. If you are a skier or snowboarder, I’d hold off on a season’s pass at this point, as the odds favor below-average snowfall for the Cascades.
Charlie is a Madrona resident, received his B.S. in atmospheric sciences from the University of Washington and works in Portland as a meteorologist. Check out his weather website at charlie.weathertogether.net.