A reminder to check out the Meteorology Memos and More Page for some fun new posts lately.
The next several days will bring relatively quiet weather to most of New England, and though this brings a much deserved break in the action, the longwave pattern of a Northeast U.S. trough will continue for the foreseeable future, to the end of July.
In the short term, the departure of Thursday night's cold front has meant a rapid infusion of dry air to all levels of the New England atmosphere. The lower relative humidity air came rushing in aloft around dawn, clearing clouds quickly from west to east as the storm center strengthening to our northeast and the bubble high pressure center over the Ohio Valley teamed to increase the pressure gradient and corresponding westerly flow at 10-20 mph. Winds verified a bit lighter than I'd thought they would yesterday, with mixing to 900 mb but only about 20 knots at the top of the boundary layer available to mix down. Dewpoints dropped steadily through the morning but should level off this afternoon before decoupling occurs in sheltered valleys this evening, allowing min temps in the 40s in cooler spots, 50s elsewhere, and a dry 60s in cities that hold the heat, like Boston and Providence.
For most, Friday is straight-forward: a quick temperature rebound as sunshine quickly modifies cool, dry air. Mixing slightly exceeds 900 mb in models progs, which would yield middle or even upper 80s, but I've gone a bit cooler than this given the proximity of the surface high and light wind, implying mixing may not be as deep as it's advertised by the computers. Nonetheless, mid 80s is supported for most spots, cooler in the higher terrain with a steep low level lapse rate lingering. It's this same lapse rate that becomes a forecasting challenge on Friday, as the cold pool aloft keeps mid level lapse rates rather steep as well. This actually lowers lifted indices to -2 all the way into Worcester County, MA, by late afternoon and evening, at the same time a shortwave swings through aloft. This shortwave is moderate in strength and with the steep lapse rates, it won't take a very high convective top to get showers. A thunderstorm may be a bit more difficult with active ice nuclei at about 450 mb, but where orographic lift assists, low-topped thunder is certainly possible. Large dewpoint depression (temp/dewpoint spread) indicates some hailstones are a possibility in the North Country. The toughest call is storm coverage, and with so much dry air around, I have to believe the most likely spot for scattered thunder will be where dynamic lift is greatest, which will be in the path of the vorticity maximum. The NMM indicates that'll be across Southern New England, while the GFS is farther north, which is the solution I favor given the fast and relatively flat flow, not to mention the surface high moving just south of the South Coast during the day, holding dry low level air in place. For these reasons, I've held the chance of scattered showers and possible thunder to the North Country.
Thereafter, I expect Saturday to be dry regionwide with a gradual moderation in temperature, and upstream temps supporting middle to upper 80s Saturday and Sunday, with dewpoints creeping back up Sunday. Disagreement among the guidance comes later Sunday and Monday with regard to thunderstorm threat, based largely upon when the feed of southern stream moisture sets up. At this point, the undeniable trend has been slower among the guidance. That said, the upper level flow is southwesterly while the low level flow becomes more southerly through 850 mb, tapping tropical moisture directly from Cuba, and with a mid to lower level shortwave embedded in the flow later Sunday, blossoming tropical showers/thunder are possible later Sunday. We're right on the cusp of a major rain event Sunday night and Monday, and this will largely depend upon how the tropical low level jet and the incoming cold front out of Ontario interact...likely to breed a band of thunderstorms and heavy rain from New York into Northern and Western New England heading into Monday. Timing on this remains tricky, but again, the trend is to keep the two features separate on Sunday - a northern stream cold front over NY and blossoms of showers in the southern stream that may move over parts of Southern new England late Sunday, with a greater interaction Monday.
This interaction doesn't last too long, with midweek high pressure settling in and anomalously cool air through the middle of the week. Thereafter, the Northeast US trough dominates, but flexes over the next couple of weeks, allowing continued shots of deep summer warmth, as we've been seeing.
No discussion slated for tomorrow...enjoy the wonderful weekend!
Matt