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Friday, December 30, 2011

Less enthused about New Years eve Clipper and about the pattern overall starting next weekend

Unfortunately, we are going to have to lower expectations with the polar pacific clipper system. It has some moisture with it as it passes through the Midwest but much of this moisture, according to some of the latest high resolution models, will get rung out over the Great Lakes. In the end, occasional light snow Friday night and Saturday will amount to 1-4 inches. This will be followed of course by the push of milder weather which is expected to impact the region on one afternoon. It will actually be a rather pleasant late December day with temperatures in the 40's but we are in much greater need of both more snow and more cold.

Much of the eastern United States will get its biggest blast of cold so far this winter. The front will arrive late in the evening of New Years Day and we are not expecting much in the way of any rain. Enough low level instability in the wake of the frontal passage should set the stage for a period of terrain induced snow showers throughout January 2nd and into January 3rd. A little too early to tell about the potential for accumulations in this time frame except to say at least an inch or two. Later in the week the large upper trough, responsible for the widespread outbreak of cold will get re-enforced briefly by a clipper system that is expected to drop into the eastern Great Lakes around the time frame of Wednesday the 4th. This system may bring some snowfall to Vermont or may bring the bulk of its effects to areas farther south.

The concern expressed a few times on the blogs relates to the lack of blocking associated with next week's cold outbreak. You can think of this as a ship reaching port without an anchor. Jet stream blocking at high latitudes is this anchor and although the North Atlantic and Arctic Oscillations have been neutralized they have yet to resemble the picture that we need to turn this thing completely around. The result will be the erosion of cold weather by next week and perhaps even another 1-2 day stretch of unneeded milder weather. I have been watching the upper level pattern in the Pacific closely for signs of a change; indeed, there are some changes but not all of them good. It will be another coupling of upper ridging in the Pacific/Polar Vortex over Alaska which will drive the cold out next weekend. The vortex of cold in Alaska however will move out of that region toward western North America allowing a somewhat more tradional La Nina set up to establish itself by January 10th or so. The result ? cold weather in western North America, warm weather in the southeastern United States and anything goes across the Great Lakes and Northeast. My guess is that temperatures between the 8-14th of the month will be above normal. We could however see slight above normal temperatures with a few snow/ice events or we could see more substantial above normal temperatures with ice and rain events. Our friends in the western United States should do very very well in this set-up.

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