Another Sunday night prospectus - the time when I sit down and look at the upcoming "big picture" in the forecast to have a foundation to build from as the week brings the need for attention to detail.
For those of you who've looked at the prognostics for this week, it's enough to do a double take for sure! Aloft, we have a series of strong upper level lows near and over the Northeast, and this is going to keep things interesting. In the short term, a formidable ocean storm develops Sunday night through Monday, stacked beneath a well defined upper low, but remains progressive and stays offshore as the upper low starts out positively tilted until it nears Nova Scotia Monday night, at which point it interacts with the fast Westerlies and gets a push out.
By that point, a new, strong shortwave is digging through the Central Great Lakes, and this one means business. It's the combination of a piece of energy from the Aleutian Low by Alaska, and the polar vortex near the North Pole. This shortwave amplifies as it nears the mean trough position over the Northeastern United States. For those of you who've been keeping up with my day-to-day discussions on WeatherNewEngland.com, you've seen my thoughts on a colder-than-normal pattern with a chance for a significant precipitation event sneaking back in. The first of this combination comes this week, as the amplifying shortwave becomes a closed upper low, transitioning from positive to neutral tilt as it moves from New England to Nova Scotia. We should get a surface low developing in the cyclonic vorticity advection and upper level diffluence ahead of the vorticity maximum, and this will continue shooting east on Tuesday. But the air aloft is so cold with the upper level low - to the tune of -27 to -28 C at 500 mb - that this provides strong mid-level instability, and a resultant inverted/Norlun trough, perhaps even with a surface low circulation along it! This is important because, with a northeast wind behind the departing initial surface low, this means a moist several thousand feet in the lower levels of the atmosphere, and cold advection that brings widespread 850 mb temperatures below zero late Tuesday through Tuesday night and into Wednesday. 500 to 1000 mb thickness values are also below the critical 5400 dm values that would indicate snow for all of New England.
Of course, this time of the year it isn't all so simple. Critical will be the lowest few thousand feet of the atmosphere, which may be moist and chilly on a northeast flow, but will have significant trouble cooling for anything but a cold, cold rain in most spots. In the mountains of Maine and the Crown of Maine, however, a northeast flow means a surface wind directly from the center of the cold anticyclone east of James Bay, Canada. At least from the big, Sunday night picture, that tells me it should be cold enough for snow in these northern and elevated areas of Maine Tuesday night into Wednesday morning, with the potential for the cold to make it into the higher terrain of the White Mountains of New Hampshire!!! The hardest part of making this happen will be the surface/near ground cold advection, but in higher terrain this is always much easier to do.
Wednesday it looks like lots of junk lingers - low level moisture, chilly air, leftover convective bursts near a lingering inverted front as the upper low only slowly moves east. Thereafter, the next huge high builds in with very chilly but dry conditions thru Friday. There are divergent solutions for what happens with the deep upper level low from the nation's midsection by next weekend, but this all clearly points to a strengthening and retrograding longwave pattern.
You guys have any thoughts on this week? Add 'em in the comments!
Matt
