Think Snow, Tweet Snow !!!

Wednesday, January 3, 2007

Arctic air ready to shake things up

There is so much to talk about today that it will take an extra effort to avoid turning this into a 5-page essay. Overall, I am happy to report that major changes are in store for the North American continent overall and although we in New England aren't exactly sitting on the winning lottery ticket, we should be able to share in some of the winnings. As mentioned in the last post, the catalyst and key to all this will be the happenings above the state of Alaska; specifically, the development of a ridge which is expected to extend poleward and beyond and allow a pipeline of very cold Arctic air to push deep into North America and parts of the United States next week. For anyone following the 3-5 forecast it is obvious that I am getting a bit ahead of myself. Mild weather is poised to advance deep into New England Thursday and into Friday accompanied by plain rain and the benefits of any of these so called "changes" won't be felt until early next week.

Mild Weather and rain ruin another weekend
I won't spend too much time on this since the drama of the uncertain is gone and the news isn't good. NWS Burlington will do at least as good of a job nailing down the specifics here but it appears as if the first batch of precipitation arrives sometime during the night Thursday or early Friday as freezing rain or plain rain. The moisture is associated with a weather system which will ultimately track deep into Quebec thus making a push of mild weather and an eventual period of plain rain inevitable. The heaviest precipitation will fall as plain rain Friday Night or early Saturday. NWS Burlington is then calling for 40's on Saturday but if the clouds were to break for a few hours of Sun and some of those very warm temperatures aloft were "mixed" down to the surface, readings could climb well into the 50's which is record territory. The gradual trend toward colder temperatures does begin on Sunday but it will still be well above normal with no new snow.

A much needed week new snow and colder temperatures
Next week gets a little dizzying for me as their are so many parts of this story to tell. After sifting through the details it appears as if two significant "clipper" impulses will bring the chance for significant new snow. The first comes late Sunday or early Monday, the second Tuesday or Wednesday. The former proves to be more of the forecast challenge. It is complicated by the fact that a wave on the tail-end of the weekend cold front may try to ride up the coast Sunday night. The result of such an occurrence could be good or bad but probably bad since if the two impulses work out-of-phase with each other then the coastal system will rob us of some of the moisture from the clipper. Once this weather system clears the region by Monday however, we should have at least a little new snow at the high elevations plus the introduction of below normal temperatures. The second clipper system should deliver some much needed new snow to the mountains, tough to tell how much since its 6 days out but whatever falls in that January 7th to January 10th period will be much needed relief.

Big Arctic cold to make a big Rocky Mountain plunge
As we are finally being re-introduced to winter in northern Vermont early next week, there will be a major league push of cold into the Rocky Mountain west and High Plains. This occurs because this upper air feature described in the opening paragraph is establishing itself over Alaska or 155 W longitude as opposed 130 W which is over the Northwest Territories of Canada. Its a significant difference and creates a looming issue for us next weekend. If everything were progress as many of the numerical models are suggesting, it would mean another push of milder temperatures and possibly a snow to ice situation for the weekend of the 13th and 14th of January. This is where the debate begins and i have been watching it rage on amongst those in the weather community.

The 1998-1999 scenario
It was a year where in January, the prevailing upper air pattern was unfavorable but with the competing force of arctic air made for continuing drama. There was snow, bouts of very cold temperatures followed by freezing rain and even rain. It was not the year of the famous Quebec ice storm, it was the year after, a year which featured not just one big ice storm but many smaller ones. The medium range models are essentially showing most of this scenario but its important to note that 1998-1999 was a strong La Nina winter, this is certainly not which in my opinion should prove to have serious ramifications on the actual outcome.

The 1992-1993 and 2002-2003 scenario
I think it is safe to say that we have not exactly followed the template of these exceptionally great snow winters. I bring the two years up however because both were "El Nino" winters like this one (02-03 was weak) and in both cases, significant east coast ridges in the Jet Stream were advertised by the models only to be busted up by the southern branch of the Jet which in the end led to more east coast snow and cold. In the case of 92-93, the busting up of the ridge occurred in the middle of February and preceded an absolutely legendary period of snowfall lasting through late March. The 02-03 case occurred at Christmas time which was also a great period of snow for Vermont.

So how do I think this plays out ?
This winter has been so lackluster (to put it mildly) that it seems almost ridiculous to make comparisons to 92-93 or 02-03. Still, in an El Nino winter, getting arctic air on the playing field is the hardest part and so long as we can do that next week, which I think we will, it will prove to be a big step in the right direction. A 3-week period of very favorable weather is not guaranteed beginning next week but very possible in my opinion in spite of what the skeptics might say. The teleconnections, specifically the AO is expected to be neutral within 5-6 days and then at least slightly negative in a week. Thereafter, the outcome with the AO is still inconclusive but its still a major shift when you add the Alaska to North Pole ridge into the mix.

The Quick Summary
Mild weather and rain set to ruin another weekend but arctic air ready to shake things up next week.

1 comment:

Alex said...

Josh, can you include some links to weather data so we can learn more about these patterns? So far I found this daily AO index from CPC that includes predictions over 7-14 days. I'd be interested in similar source info for the polar ridge over 155W vs 130W, the current Jet Stream situation, and historical effects of El Nino on the NE US...

By the way, fascinating topic! Thanks for writing this.