Abstract
Abstract During the week of Christmas 2021, winter storms pummeled the Pacific Northwest and broke daily temperature and snowfall records in scores, especially west of the Cascades and notably in Oregon. With La Niña ruling the tropical Pacific, the record-setting, disruptive snowfall during Christmas week raised questions about its origin, especially as the seasonal outlook was for below-normal precipitation. We show that Pacific–North American (PNA) teleconnection—a well-documented subseasonal variability pattern during winter—reigned over the region in its negative phase; it was the strongest 7-day PNA episode in December in more than 50 years. It led to robust northwesterly onshore flow, whose interaction with the Coastal, Cascade, and Sierra ranges led to blockbuster snowfall and precipitation. Note that one seldom encounters circulation anomalies consisting of just one winter teleconnection pattern. Also worth noting is the tremendous power of subseasonal variability in recharging Western water resources in the context of the seasonal gloom from a La Niña–intensified West Coast drought.
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