A dome of high pressure cresting over New England is locking in a stretch of fair weather, though a persistent onshore flow will bring varying amounts of clouds to eastern parts of Southern New England in the coming couple of days. The stretch of fair weather will continue for quite some time, lasting through the upcoming weekend when temperatures will climb across the Northeast and record high temperatures may be set early next week.
In the meantime, it may not have been record cold but it certainly was a chilly start Monday morning across New England with frost at dawn across many communities in Northern and Western New England, and the deeper valleys of Central New England, and fog in some other valleys that burned off after only a couple of hours of sunshine. The remainder of Monday has been the second fine fall day in what will be an extended stretch, featuring the center of a high pressure cell lodged over Northern New England with light and variable winds in the North Country and a light northeast wind under the belly of the fair weather cell elsewhere in New England, set in motion by the clockwise flow of air around the center of the high pressure dome. Of course, while one result of an onshore flow is to keep coastlines cooler, the other result is to add moisture to the otherwise dry air as the wind picks up water vapor from the Atlantic Ocean. As this increasingly moist air moves over the land of Eastern Massachusetts on the northeast wind, the warm land contrasted with the cool sky allows this water vapor to rise, cool and condense, forming puffy white cumulus clouds. These will be fair weather clouds Monday afternoon, though a few may lower just enough in the sky for pilots to observe an isolated patch of marginal visual flight rules.
With the setting of the sun and our dome of high pressure only very slowly inching east toward New England waters and locking New England firmly into dry air, any cumulus clouds will melt away to give way to clearing skies, and winds will become nearly calm, allowing excellent conditions for radiational cooling (remember, you can double click on words like "radiational cooling" to see the definition from answers.com). As the heat from our warm ground escapes skyward, temperatures will once again fall into the 40s south and 30s in northern, central and western New England, especially in valleys where a renewed round of frost is likely.
Tuesday morning will once again dawn with sunshine that will provide a quick rebound in temperature for New England, boosting most communities to either side of 70 by day's end - still a degree or two below normal for the date, but quite pleasant for one and all. As high pressure shifts east of Maine Tuesday afternoon, a northeast wind will continue, and an input of moisture will continue to allow development of puffy cumulus clouds Tuesday afternoon. Meanwhile, south of the dome of high pressure, a weak wave of low pressure will develop in the lowest few thousand feet of the atmosphere, and the counter-clockwise swirl of air around it may launch some low altitude clouds far enough north to move over Cape Cod Tuesday evening and night, and linger into Wednesday morning, perhaps even producing a bit of drizzle as this shallow moisture moves west and backs into eastern coastal locales of Southern New England. Admittedly, we'll find ourselves just barely on the western edge of these clouds and it's possible they don't expand westward as much as forecasted, but given that the push comes overnight Tuesday night, the cool conditions of the overnight do favor some of this moisture expanding into Southeastern New England.
Regardless, any deck of moisture should erode from the edges inward toward the center of cloud cover Wednesday morning, yielding another day of sun and clouds with temperatures very close to normal. Most of New England is likely to find ourselves in a sliver of warmth behind the high pressure cell, sitting offshore and providing a southwest wind behind it, and ahead of an approaching cool front defining the leading edge to another push of Canadian air settling south across Quebec. In this sliver of warmth, temperatures should come to either side of 80 in many New England communities with the aforementioned cool front settling over New England but not entirely sweeping south of the region, providing cooler air but still a mild and pleasant day that will likely end up at least a few degrees above normal.
The upcoming weekend will put the squeeze on between a moderately strong storm cutting across Southern Ontario and Quebec, and the stubborn bubble of high pressure that will, by that point, be drifting southeast of New England. At the surface, this provides a continued west and southwest flow of air, and it's unlikely much cool air would settle south, allowing warming in the lower levels of the atmosphere. Meanwhile, a major change will be shaping up aloft, high in the sky at the jet stream level. Remember that the jet stream winds are the fast winds tens of thousands of feet high that flow like a river across the planet, steering storms and acting as a thermostat for the atmosphere with cool air to the north and warm air to the south. By the end of this week and the upcoming weekend, the persistent area of high pressure along the Eastern Seaboard will merge and bridge with a large ridge of high pressure over the Atlantic, creating a mammoth jet stream ridge - a bubble of warmth and relative high pressure - from the Eastern United States into the Atlantic Ocean. To our west, a significant chunk of cold Canadian energy will dig a trough, or dip, in the jet stream across the Western United States, further locking in the pattern of a bubbling Eastern United States ridge and thereby forcing warmth northward deep through the atmosphere, until record warmth may be attained early next week in the Northeastern corridor. As for our chances for rainfall, large ridges of high pressure tend not only to bring warmth but also dry air, and significant precipitation seems unlikely for the next week, while this ridge remains in charge of our weather pattern. Eventually, the ridge will break down and when it does, this should allow a tap of moisture directed from the Gulf of Mexico to the Great Lakes to move east, and that may happen by the middle of next week.
Have a great Monday.
Technical Discussion: A bit behind the 8 ball today. Will try for one tomorrow.
Matt
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