Riskpulse, the leading provider of weather risk analytics for supply chains, has released their 2017/18 Winter Outlook. This outlook builds on an earlier October report that catalogued the ‘given’ variables going into the season and their likely impacts: these ‘knowns’ included the overall trend of warmer winters over the past few decades and the equal odds of a cold/warm winter during La Niña events.
Now Riskpulse possesses substantially more information about the conditions underlying this winter’s weather. The short version is that the southeast and east coast should expect a warm winter—but cooler than the past two ‘megawarm winters’—and drier conditions. The northwest and Great Lakes regions should expect a somewhat colder bias and more active storms with precipitation. Riskpulse forecasts a large western zone of increased risk of transportation disruption from Vancouver, east to Winnipeg, south to Sioux Falls and Denver, and back west through Salt Lake City to Eugene.
We break down Riskpulse’s thinking on these forecasts below.
The Polar Vortex, a large-scale low pressure zone that rotates counter-clockwise above the North Pole, appears to be relatively strong, circular and stable, although that can change. A stable Polar Vortex with strong rotation will maintain a circular shape and will be less likely to leak Arctic air into lower latitudes in Canada and the United States; a weaker Polar Vortex tends to deform into an elliptical shape that can send frigid air flowing southward. In this outlook, released on Monday, Riskpulse expects the Polar Vortex to remain strong at least through early December.
Sea surface temperatures (SSTs) can be used to predict long-term atmospheric pattern evolution because of their relative stability—it takes a long time for large ocean regions to change temperature. In their report, Riskpulse includes a map of current SST anomalies worldwide. The northern Atlantic appears warmer than usual while the equatorial Pacific has a band of colder anomalies. Riskpulse says this is consistent with a warmer, drier outlook for the American southeast and eastern seaboard and a colder, wetter forecast for the American northwest.
The snow cover in northerly latitudes in the mid fall can indicate how much Arctic air is forming as winter approaches. As of early November 2017, snowpack is roughly normal, in the middle of the distribution for the past 10 years. Riskpulse reads this as a ‘neutral variable’—it does not contribute to either a colder or warmer winter forecast.
On temperature, Riskpulse concludes, “Hence, the region with an increased risk this winter of longer duration cold is the Pacific Northwest, Northern Rockies, Northern Plains and adjacent areas in Southwest Canada. The eastern and southern U.S. have the highest probabilities for warmer than normal temperatures.” With regard to precipitation, Riskpulse’s meteorologists write, “Winter storms are more likely from the far western Great Lakes to the Pacific Northwest; this includes adjacent areas of Canada. Storms are less likely compared to normal in the southern U.S. and along the East Coast. We feel that the total number of Nor’easters this season will be less than normal.”
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