Thursday and Friday mornings (January 9 and 10, 2020) saw some light snow throughout the Puget Sound region, but with little or no accumulation. A slight warm up followed on Friday afternoon and continued into Saturday. On Sunday, however, big changes are on the way. Outflow from the Fraser River Valley in British Columbia should start making its way into the Puget Sound by late Sunday afternoon. Plummeting temperatures are then expected through the middle of next week with lows in the teens and highs below 300F (degrees Fahrenheit).
As we get ready for the cold and possible snow, it is interesting to review past winter weather in Seattle. Statistics from SeaTac Airport are the most comprehensive, so let’s take a look at those. Temperatures in Seattle have clearly moderated in recent years. The lowest temperature ever recorded at SeaTac Airport was 00F degrees on 31 January 1950. In fact, 1950 had eight of the 11 coldest days in SeaTac history with low temperatures ranging from 00F to 70F. The last time SeaTac recorded a temperature below 200F was a 190F reading that occurred in December 2013. It is possible that the coming cold spell will see the coldest temperatures of the last decade.
But what about the possibility of significant snow this coming week? That is a tricky question. Historically, there have been some very snowy months in Seattle history. The snowiest month ever was January, 1950 when 57.2 inches of snow fell. In the period December 1968 to January 1969, a total of 67.5 inches fell. Just last February 20.2 inches of snow accumulated, making February, 2019 snowiest month since January, 1969.
Although the recent forecast models that have been consistent in predicting very cold temperatures, the timing and amounts of any moisture are unclear. For snow, not only do we need cold air, but we also need a moisture source. Frequently, an intense but short-lived snow event accompanies the initial outbreak of cold air from Canada’s Fraser River Valley. This is a possibility, for at least part of the region, Sunday night. The forecast models are indicating the possibility of moisture coming into Puget Sound by late Wednesday (15 January). We shall wait and see.