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Livestock Wx for November 3, 2017: Discusses the potential for a cooler than expected winter over parts of the south-central and southeastern U.S.
While the current La Nina is likely to have the greatest impact on the Central and Southwest U.S. (i.e. above-normal winter temperatures), there are other weather and climate variables which could impact key U.S. cattle-producing regions.
One of these factors is the Arctic Oscillation and its relationship with the current Eurasia snow cover.
You might have noticed that NOAA’s winter temperature outlook keeps milder weather to the south and hints at a “dip” in temperature anomalies over the North Central U.S. and into parts of the Midwest. Could this hint at a persistent dip in the jet stream (red-dashed line), and an unusually harsh winter, over the middle of the nation?
The Arctic Oscillation (AO) is a climate pattern characterized by winds circulating counterclockwise around the Arctic at around 55°N latitude. When the AO is in its positive phase, a ring of strong winds circulating around the North Pole acts to confine colder air across polar regions. This belt of winds becomes weaker and more distorted in the negative phase of the AO, which allows penetration of colder arctic air-masses and increased storminess into the mid-latitudes.
An amplified dip in the jet stream, primarily over the Midwest and Southeast U.S. can represent a negative phase of the AO.
The predominant phase of the AO very well could determine the harshness, or not, of the upcoming weather season.
The AO will alternate between positive and negative phases during a typical winter; however, the predominant phase during the core 8-week period from late December through early February can shape the entire winter season.
Unfortunately, there is not much skill in predicting the AO outside of several weeks. While predictability is limited, new research indicates there could be a strong linkage between an increase in Eurasian snow cover in October with colder winters over parts of the southeast and eastern U.S.
Widespread deep snow cover effectively reflects sunlight back into space and allows dense and extremely cold air to remain near the earth’s surface. A significant increase in Siberian snow cover in October tends to enhance the potential of a negative AO during the winter. Eurasian snow cover stalled for a while in October but picked up again late in the month. Currently, Eurasian snow cover is above normal and similar to last year at this time.
Take Away: If the AO is persistently-negative during the core 8-week winter period, it could be an unusually cold winter across parts of the Midwest and Southeast U.S. While AO predictability is limited, at this time, there are some signs pointing towards a negative wintertime AO, which would significantly alter NOAA’s winter outlook.
Livestock Wx will continue to track the status of the AO and report on its status throughout the winter.