Cooler temperatures return but we are dry for another week

Across the entire continent of North America, there is only significant weather producer. Its a significnat one, a blizzard, poised to bury much of eastern Colorado with snow. Eastern Colorado and western Kansas are lonely places however, void of mountains and most vegetation. Resorts such as A-Basin, Keystone, Copper, Vail and Aspen are in the central and western sections of Colorado, west of the divide. Those areas will actually only get a few inches out of this storm proving that it has been a very painful year for almost everyone. The exception ? The Canadian Rockies which has reaped the benefits of the same very active Pacific Jet stream I have been groaning about all year.

The "loosening" of this active Pacific Jet will occur on schedule and the result will be the development of a large upper level Ridge across western North America. This feature will be the biggest in the Northern Hemiphsere for a period of a few days, so big in fact that it will take longer to funnel cold toward the eastern third of North America. Temperatures will be close to seasonable this weekend but the "blizzard" across the western Plains will not have a reinvigorating catalyst when it moves east and it will innocently move toward the Mid-Atlantic coast late Saturday then off the coast Sunday without threatening any part of New England with precipitation.

The beginning of next week is also expected to be benign with temperatures making another charge toward above-freezing levels Monday afternoon. Tuesday should see more clouds as the front marking the leading edge of colder temperatures marches southeast. This front will be riding the momentum of the aforementioned western ridge, it doesn't have much in the way of moisture to work with but flurries or a brief period of light snow is possible Tuesday and Tuesday night before another we enjoy another dry and seasonable day Wednesday.

The next chance of significant snow will come toward the end of next week in what appears to be an interesting time frame. As next week continues to progress, the ridge across the west will allow a polar vortex to move south from the polar regions to eastern Canada. Recent runs of many of the computer models have suggested that the impact of this "PV" will be confined to eastern Canada and the northeast U.S. next weekend. Certainly it could result in some of the coldest weather of the season but we are in dire need of a bit more than just bitter chill. We need some of this "PV" energy, even a small piece of it, to combine with undercutting Pacific energy to produce a storm. Its not an impossible task but requires "split flow" in the jet stream. The polar component of the flow looping around the western ridge deliving us the cold and upper air support and a southern branch of the jet delivering the moisture. We haven't heard much talk of "split flow" the last two years since La Nina makes it a tough sell. I would love to see it return however since it has certainly provided us with some epic times.

So we think a vague picture has emerged regarding next weekend including cold weather and hopefully at least a little new snow. Beyond that however begins an all out war between the two major ensemble packages. It is one of the biggest disagreements I have ever seen in the 10-15 day time frame. Interestingly, both ensembles keep a blocking pattern in place through the AO. The European however destroys the western ridge completely, showing another sharp tightening of the Pacific Jet and ultimately a return to zonal flow across the country. The American GFS weakens the western ridge but does not eliminate it. Instead, ridging that stretches from the North Atlantic, over Greenland and to the poles evolves gradually into a large "block" that allows for a continuation of both cold and frequent chances for snow. The European has been winning these arguments for much of the year but this battle has not been fought with the underlying teleconnection indices as favorable as they are now. I remain frustrated but have not abandoned hope.