Predicting winter weather? Fred has the ins and outs of making the forecast

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Winter Weather Outlook Web Extra_20151030020303

ABC9 Chief Meteorologist Fred Hexom predicts that the upcoming winter will be relatively mild. This is due largely to warm ocean waters along the equator in the Pacific Ocean, a phenomenon known as El Nino.

There is a 95 percent certainty that El Nino will remain in place over the winter and into the spring. The effect of this El Nino will be to produce above normal temperatures in Siouxland and much of the north central United States. El Nino is not a storm, but rather an atmospheric condition that influences the jet stream, and subsequently the temperatures and precipitation we experience.

Another factor Fred looked at is the Arctic Oscillation. The Arctic Oscillation, or AO, can be described as a belt of winds circulating around the Arctic. These winds act as a fence to keep cold air confined to the poles. When the AO goes into a negative phase, the “fence” breaks down and cool air spills southward, clashing with warm air to its south and producing stormy weather.

The AO has recently gone into the negative phase after being positive for much of 2015. It’s too early to determine if this trend will continue long enough to have an effect on our weather, but the fact that the AO has recently trended negative gives some early and tentative support to seeing snowstorms develop this winter.

Also, if we look at the AO in December 2009, we see a very sharp dip in the negative direction. This correlates well with a memory still fresh in the mid of many in Siouxland: the Christmas Blizzard of 2009, which dropped 20.7″ of snow on Sioux City over four days.

Fred Hexom and Siouxland’s Weather Team will keep you up to date on winter weather this season, tracking Fred’s progress as we go along.

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