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Monday, February 5, 2007

Frigid temps through the weekend; temperature moderation next week could be an interesting twist

The underscored word of the week is "cold" of a widespread and very intense variety. Many cities across the Midwest are falling below zero for the first time in several years. The cold, in this instance isn't centered around New England. In contrast to what occurred on January 26th, this cold is centered across the upper Midwest where temperatures on a frigid scale are as impressive as December of 2000. At this risk of getting a little geekish, check out this colorful map which shows current temperatures across the country. I like this map because it shows a good percentage of Canada and depicts how the cold is configured around the Great Lakes.

http://twister.sbs.ohio-state.edu/surface/ustemp.gif

General Stark did pick up a dose of new snow, mainly Friday night but I am jealous of the Great Lakes. Those snowbelt areas are embarrassing us, particularly the tughill plateau in New York where some places seem to be picking up 1-2 feet of the good stuff every day. The lake bands this weekend were very condensed as they often are when extremely cold air moves over the lakes from the west-southwest. Whatever was left of the plume of moisture after it crossed the Adirondacks affected a limited area of the northern Green Mountains (Jay Peak). The heaviest snow bands have since shifted south and as of Monday morning there were a few snow showers over Mad River and points south. These could drop 1-3 wind driven inches on the mountain today and tonight so enjoy it if you can endure the cold.

No better than 10-degrees (-12 C) all week and usually much worse
The north country will be free of major weather systems through the weekend; instead, it will remain cold with temperatures failing to make it above 10 on the mountain through most of this week and possibly through the upcoming weekend. There are some small undulations in the intense polar jet as impulses rotate around the vortex of cold which is currently positioned near the Great Lakes. The first such disturbance impacts the region Wednesday or Wednesday night which could provide the high terrain with a re-freshening few inches of powder for Thursday although it doesn't look like much. The passing of this disturbance will allow a build up of brutally cold temperatures in Ontario/Quebec to drain over northern New England and thus create the two coldest and windiest days of the week Thursday and Friday.

First close-up look at the upcoming polar weekend
Model guidance has had difficulty timing some of these smaller weather systems because they are caught in this mammoth polar jet. One such system appears as if it will impact the region this upcoming Saturday but the if, the how, the when and about everything appears up in the air. Its not a significant weather system; but nonetheless, it brings us the chance for much needed new snow on the all important weekend day. The system will arrive as the last of the most intense pieces of the Polar Vortex rotates into the Great Lakes and into New England. This jet has been so incredibly energetic that it has been difficult for any of the smaller short waves (waves within bigger waves) to maintain any real potency and thus the impression prevails that we are under-achieving in this pattern. The capriciousness of the models certainly offers no certainties but its something to watch over the next two days since the outcome of this system may make the difference between a 6 inch snow weekend or a 1-2 inch snow weekend. I can make the determination that Sunday appears the colder and windier of the two weekend days although to reiterate, neither day is likely to see temperatures much past 10 on the mountain if at all.

The Big and Important Long Range Discussion
Beyond the upcoming weekend will bring us to our first potentially adverse situation. For the last few days the ensembles have been keying on the 14th-16th (Wednesday-Friday) of February as a mild group of days based strictly on jet stream anomalies. A big cause of the change will be the elimination of the high amplitude western ridge, which at this point will have migrated to the poles (more on that later). This will allow the western states to become unsettled while much of the eastern half of the country experiences a temperatures moderation. There are strong indications that a significant storm system will gather strength across the south during the middle of next week and then track northeast into the decaying cold air. If the rotting cold were to get scoured out quickly and the storm were to take the worst possible track, we could find ourselves getting precipitation other than snow only a few days after experiencing brutal cold. That being said I in no way think this happens. The break down of the western ridge is likely to occur but much of that blocking migrates to the pole which keeps the AO (Arctic Oscillation) safely in negative territory. The negative index indicates that arctic air is unlikely to give up its grip on the northeast without a drag-it-out fight which is what we want. In other words, what looks like trouble could turn out to be a significant snow producer in the best case scenario.

Someone sent me an email about links to these teleconnection indicators so I will provide a few here.

AO - http://www.cpc.noaa.gov/products/precip/CWlink/daily_ao_index/ao.sprd2.gif
NAO - http://www.cpc.noaa.gov/products/precip/CWlink/pna/nao.sprd2.gif
PNA - http://www.cpc.noaa.gov/products/precip/CWlink/pna/pna.sprd2.gif

After February 16th would bring us to the President's day holiday if I have my calendar correct. The warm-up next week is shown to be temporary and quickly replaced by another surge of below normal temperatures. The return to colder weather has the support of the AO as I mentioned above but there is no indication of a strong ridge in western North America. This would suggest that the cold will not be as intense nor as long in duration. I should be careful however with this statement because the weather becomes increasingly volatile climatologically in late February and early March and although a pattern as a whole may not match up to the last two weeks or next 7 days, individual weather or temperatures events are certainly capable of impressing.

The Quick Summary
Cold dominates through the weekend with new snow falling in small increments. Temperatures try and modify significantly as a storm system approaches next week. That could be bad or good but I am thinking good as far as new snow goes.

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