According to new research, Washingtonians shouldn’t blame bad luck for the recent string of high-impact snowstorms, from “Snowmaggedon” two years ago to last January’s “Commuteageddon.” Instead, it may be more justified to cast a suspicious gaze toward Siberia, about 6,000 miles away.
Famous for its bone-chilling cold, Siberia typically starts building a snow pack during October, and the speed of its transition from tundra to snowscape helps to shape winter weather throughout much of the Northern Hemisphere according to a new study...
Cohen’s study unveils a new index, called the Snow Advance Index (SAI), that skillfully predicts the phase of the coming winter’s Arctic Oscillation (AO), based on the growth of Siberia’s October snow cover. Historically, he reports, the index has explained “close to 75%” of the AO variability.
Readers of this blog know that when the AO tends negative during winter, it strongly favors cold, snowy conditions. But historically, forecasters have stopped short of trying to predict it. For example, NOAA has described the AO as a “wild card” in seasonal forecasts.
But Cohen’s study concludes: “...the AO, while thought to be unpredictable, may in fact be one of the most easily predicted phenomenon known in the climate system.”
This viewpoint isn’t universally accepted, and Freedman’s article discusses some alternative ideas.
Irrespective of whether the AO is as predictable as Cohen claims, inquiring minds surely would like to know what Siberia snow cover has done this fall. Freedman’s piece offers the scoop:
Siberian snow cover advanced at almost exactly the normal rate during most of October, with the exception of a dramatic expansion at the end of the month, which has Cohen a little nervous about this year’s forecast. Without a clear Siberian snow signal, he relied more on other factors to make his forecast, including the likelihood of continued La Nina conditions in the Pacific.
In light of all the above, Cohen is predicting a milder than average winter in D.C. and along the East Coast with near normal snowfall. In an email to me today, he offered a little more detail:
I feel that the snow-atmosphere coupling this fall continues to favor a milder winter in the East.
I think the winter starts off overall mild in the East and the better chance of more persistent cold is later in the winter.