Snow marked the leading edge of warm and moist air surging in for many communities in Central and Northern New England - and parts of Southern New England, too - but this happened with a southerly wind which means it's not long to last in the most Central and Southern areas. Nonetheless, reports of a solid coating to an inch are coming back from especially elevated inland terrain. Warm advection continues on a southerly wind overnight as dewpoints rise and temp is forced upward overnight will result in areas of fog that will be most dense along the South Coast. Fog and low clouds will start the day Tuesday but a pocket of drier air from 800 mb upward comes thru midday onward and should induce breaks in the overcast, esp with the assistance of downsloping flow. With such a mild air in place - producing highs in the 50s and 60s today under plenty of clouds to our south and west - it should be easy to break 60 where the sun emerges and widespread 50s are anticipated elsewhere. Convective available potential energy (CAPE) climbs to over 250 J/kg in Western New England in advance of the vorticity maximum that will fire a line of convection to our west that should carry into New England during the afternoon and evening. These prefrontal storms should come in two rounds - and I'm uncertain of which one will have the best focus. The first is with a mid-level shortwave riding ahead of the main energy center and ahead of the surface front. This will have less instability to work with as it moves from 18Z in Western New England to a position off the coast by 00Z. At least some convective activity seems likely with this line. The next comes along the surface front, which will feature great low level convergence and available surface based instability, but drier air aloft and lower topped convection. Any storms that do develop in the first round will feed off of a moist sounding to produce heavy downpours and the potential for wet microbursts in an environment featuring 50-60+ kt winds through a very deep layer of the atmosphere, mostly unidirectional out of the southwest, implying straight-line wind damage is a threat with the afternoon convection from 18Z onward, and winds will remain strong for the evening line, too.
It's over Tuesday night and dry/cool advection settles in for a nice Wed/Thu. Next storm has huge differences between the guidance for Friday, with the ECMWF, Canadian GEM and GFS running the gamut, but most agree on a healthy tropical tap into New England for developing precip. The concern I have is lingering cold in Northern New England so I've kept a chance of some snow there.
Matt
This would be the areas first Spring thunderstorm assuming Matt isn't playing us for fools.
Posted by: Tom | Monday, March 31, 2008 at 04:14 PM