Visualize: Insights that power innovation

Visualize: Insights that power innovation

AER winter forecast predicts mild temperatures in northern and eastern U.S., cold in the southwest

By Judah Cohen  |  October 19, 2018

The 2018–19 winter forecast shows below-normal temperatures for the southwestern United States, the Central Rockies, Northern California, and Southern Oregon, with above-normal temperatures in the remainder of the country, including the northern and eastern U.S.

Above-normal precipitation

The winter precipitation forecast shows above-normal precipitation across much of the country, especially the Northern Rockies and along the East Coast, and below-normal precipitation across the Pacific Northwest.

The predictors that go into AER’s forecast include El Niño/Southern Oscillation (ENSO), October Eurasian snow cover extent, Arctic sea ice concentration, and an index that measures high-latitude blocking. October Eurasian snow cover extent is currently below normal; Arctic sea ice extent is below normal; and blocking at high latitudes so far this fall has been less active compared with recent years.

Below-normal snow cover and a lack of blocking favor a mild winter in the eastern U.S. An El Niño is also happening this winter, which favors a cold winter in the southeastern U.S. However, the signal is weak enough that other predictors are dominating the temperature forecast. This is a preliminary forecast and will be updated next month as more data becomes available.

The AER winter forecast has been widely acknowledged for its accuracy last winter in predicting cold temperatures with an active storm track. Last winter was one of extremes—with record cold, four consecutive nor’easters, and even record warmth. AER has tried to improve on seasonal forecasts that rely exclusively on ENSO by including information from high latitudes, an area of active research and the subject of many scientific articles at AER.

Much of last winter’s extreme weather was related to variability in the polar vortex. The climate and forecast communities are realizing the importance of the polar vortex on winter weather; and we believe that snow cover, sea ice, and high-latitude blocking are very good predictors of the behavior of the polar vortex. Two of our three indicators suggest that the polar vortex will be relatively strong this winter, potentially bringing extended periods of relatively mild weather to the Northeast this winter.

Dr. Judah Cohen is director of seasonal forecasting at AER.