The findings may help improve winter forecasts for the Washington area, which now are often of limited value because meteorologists can’t reliably predict the behavior of a highly influential and fickle weather pattern known as the Arctic Oscillation.
The oscillation helps determine the placement of Arctic air masses, and it influences how they move. When the pattern is in a “negative” phase, cold air gets drawn down from the Arctic and into the United States. Most of Washington’s snowiest winters have occurred during such a phase, including the record-setting 2009-2010, when more than 56 inches fell.
In other words, a negative Arctic Oscillation may be a D.C. snow lover’s best friend.
When the oscillation is in a “positive” phase, cold air tends to get bottled up in the far north, leaving the eastern United States milder and drier than average.
Thinking positive
Improved seasonal forecasts would enable weather-sensitive businesses as well as households to better prepare for upcoming swings in temperature and precipitation, thereby reducing economic losses. More-accurate seasonal outlooks would also permit cities and towns to set more realistic snow removal budgets and take other actions to prepare for a particularly snowy winter.
The trouble is, despite sophisticated computer models and networks of air, land and sea observations, the oscillation still frustrates most forecasters’ attempts to anticipate its behavior.
Cohen thinks he knows how to change that. His study, recently published in the journal Geophysical Research Letters, shows a statistically significant link between the rate of change in Siberian snow cover during October and the dominant phase of the Arctic Oscillation during the following winter. A rapid advance of Siberian snow cover, Cohen and his colleague Justin Jones found, is linked with the negative phase. A slow advance, by contrast, is linked with a positive oscillation, which brings milder winter weather to Washington.
Cohen claims that rapidly advancing snow cover in Siberia can set off a chain of events from Earth’s surface to the stratosphere. The quick expansion can lead to a large dome of cold high pressure over Siberia. That dome, in turn, perturbs the jet stream so it flows more north to south in addition to west to east, resulting in more intense cold-air outbreaks in eastern North America and western Europe, which often breed snowstorms.
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