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Date: 10/16/2013

Title: Rest of October and Arctic Oscillation

The month of October has been a cold and stormy one for the Northern Rockies and Northern Plains. All indications suggest there is more cold weather on the way not only for the Rockies and Plains but for many areas of the Corn Belt and east as well.

The 8 to 14 day outlook below is calling for much below normal temperatures in many areas of the USA. There will also be periods of rain/snow in many areas from the Rockies east. The colder weather cold last through Halloween and into early November for many areas.



 The Arctic Oscillation

One reason we are seeing some early season snow and cold in many areas is that we are experiencing some negative phases of what is known as the Arctic Oscillation.

While not as well known or discussed as much as El Nino or La Nina, the Arctic Oscillation is quickly becoming well known among meteorologists and others who track weather and climate.

You won’t hear about it during the nightly news during the local weather segment or even on your favorite cable tv weather program, however, you will read about how the Arctic Oscillation is behaving on this blog during the winter season.

Unlike El Nino and La Nina which are weather phenomenon based in the Pacific Ocean (warmer or colder than normal ocean waters), the Arctic Oscillation is all about what is going on in the polar regions.

Arctic Oscillation is an atmospheric circulation pattern in which the atmospheric pressure over the polar regions varies in opposition with that over middle latitudes (about 45 degrees North) on time scales ranging from weeks to decades.

It comes in two phases, a positive phase and a negative phase. In the positive phase, higher pressure at mid latitudes drives ocean storms farther north, and changes in the circulation pattern bring wetter weather to Alaska as well as drier conditions to the western United. In the positive phase, frigid winter air does not extend as far into the middle of North America as it would during the negative phase of the oscillation. This keeps much of the United States east of the Rocky Mountains warmer than normal. A negative phase of the Arctic Oscillation can lead to major cold outbreaks in the lower 48. This was especially true in February 2010 when severe cold hit most of the nation.

To whittle this down to layman terms, whenever we discuss a negative phase of the Arctic Oscillation during the winter, expect a higher probability of colder temperatures and winter weather to develop over time. A positive phase can mean warmer, less “winter like” weather conditions. Interestingly enough, many Arctic cold outbreaks across the USA happen when a strongly negative phase turns positive. This is because cold air can build during a negative phase and be released and pushed south during the phase change. 
As we head into winter, there are strong indications that Arctic Oscillation may be strongly negative at times, so keep the mittens handy and snow shovels as well, especially in the Rockies, Northern Plains and Upper Midwest.