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Date: 11/25/2013

Title: Blocking Patterns and Arctic Surges

Last week we hinted at the possibility of sharply colder conditions across many areas of the USA as we head into December. Since then, our confidence is growing that a large portion of the USA will experience very cold temperatures for the first 10 to 14 days of December.
The reason for our confidence is based on a jet stream pattern forming that is primed to drive very cold air from the high latitudes south into the USA. A strong ridge of high pressure will be developing next week in the Gulf of Alaska this will help drive cold air south out of Alaska and the Yukon to the south. Enhancing that flow of cold air form the north will be another big ridge of high pressure near Greenland. These two big ridges of high pressure will act as “bookends” to the Arctic air over the northern latitudes helping to drive very cold air south into the USA and at the same time help to hold it in place. This pattern “blocks” any major jet stream pattern changes for days and sometimes weeks.

The graphic below illustrates this pattern. The black line represents the mean jet stream pattern in early December with the high pressure ridges in the Gulf of Alaska and Greenland areas.

The Thanksgiving week will be dominated by cold and stormy weather in the eastern sections of the USA while generally quiet weather will be found in the central and western areas of the USA.

Next week is when we expect the above illustrated weather pattern to develop. The end result will be much colder temperatures and some snow for many areas of the USA from the Pacific Northwest east across the northern Rockies and into the Plains and Midwest, eventually reaching the eastern and southeastern states as well.

The cold and snow will be a concern for stock growers as the potential for severe cold, cold wind chills and snow will be possible in many areas next week and the week following. This cold snap will eclipse any cold snap that occurred during the December of 2012.

Stock growers are urged to keep a keen eye on the expected weather between the dates of December 3rd to December 15th. More cold and snow could also occur during the second half of the month.