La Niña Dissipates in the Pacific Northwest

By the time you’ve picked up this 352nd issue of the Leschi News, La “Niña” will likely have been replaced by her cousin, La “Nada,” which is the moniker we’ve lovingly given to ENSO-Neutral conditions in the Tropical Pacific, where we are neither in a La Niña or an El Niño state. “ENSO” simply refers to “El Niño Southern Oscillation” and is the broad term that describes the oscillation between El Niño, Neutral and La Niña conditions in the Tropical Pacific.

While La Niña’s effects are most pronounced after January 1, La Niñas exert some influence on large-scale atmospheric patterns earlier in the winter, and December and the first half of January featured uncharacteristically calm weather for a La Niña winter over our area as large, persistent ridges of high pressure repeatedly formed over the Pacific Northwest. La Niñas are typically characterized by an active, northwesterly storm track that keeps us cooler and wetter than normal, delivering copious amount of snow to the mountains. Though these ridges were interspersed by wet systems that brought moderate amounts of snow to the Washington Cascades/Olympics, these systems dropped very little snowfall to areas further to the south. I went skiing on Mt. Hood during late January and encountered all sorts of early-season hazards on many of the runs. The Southern Oregon Cascades were in even worse shape, with many spots barely receiving 20% of their normal snowpack by mid-January.

However, La Niña made up for lost time later in January and February, and though March was relatively calm, the first half of April was extremely cold and wet, dumping copious amounts of snow in the mountains in the process. As of mid-April, every single region in the Washington Cascades/Olympics had above-normal snowpack, and even Mt. Hood’s snowpack was close to average.

ENSO forecasts are typically very poor at this time of the year because the low-level winds that drive the changes in ocean circulation that lead to the development of El Niño and La Niña events are weakest in the springtime. Most models show us staying in a neutral pattern or transitioning to a weak El Niño by the end of 2018, but I wouldn’t put too much stock into these models just yet. Interestingly, last year’s models at this time had a similar forecast, yet we ended up going against the model consensus into a La Niña. We’ll have a much better idea of what state the Tropical Pacific will be in for the following winter by the time the kids put away their books for summer break.

I hope you’ve been enjoying the sunshine! After a long winter and a dreary spring, it’s wonderful to finally get a taste of summer.

~Charlie Phillips

Charlie Phillips, a Madrona resident, received his B.S. in atmospheric sciences from the University of Washington and works in Portland as a meteorologist forecasting wind energy along the Columbia River Gorge. Check out his weather website at weathertogether.us.