Another day that doesn't end - thus the 6 PM post as I finally have time to share some thoughts on the weather for you night owls who are interested. I promise to keep it short.
Basically, the attention in the coming days will be on the front that's draped across PA with showers. This front is stationary at the surface, but has varying intensity of warm and moist advection from 850 mb to 700 mb dependent upon each midlevel shortwave rippling through the flow ahead of an amplifying ridge. So, the overall theme to really grasping the forecast, at least in this meteorologist's opinion, is the idea of a slow moving but well defined low level front that will flare up with the passage of shortwaves, but also will quiet in the anticyclonic vorticity advection and subsidence behind them, with the constant cloudy exception to that rule found in the immediate vicinity of the frontal boundary. This was evidenced in PA today, and will probably continue to play out over the life of the front. Of course, with an amplifying ridge building into the Northeast in the coming days, there will be warm advection through a broad layer several thousand feet off the ground. Hence, the abundant cloud cover over a large area of the cool side of the front with the passage of shortwave induced warm advection. If not for the fact that confluent flow will remain east and northeast of New England thanks to the stalled upper low northeast of Maine, we'd be able to burst the late spring warmth of surface temperatures in the 70s and 80s up the remainder of the Eastern Seaboard from the Southern Mid-Atlantic and Appalachian Mountain Chain, and warm up quite a bit here in New England. But the trick this time around is that confluent flow in the middle and upper levels - favoring a surface anticyclone building/maintaining just east of New England and holding an easterly component to the wind that will keep cooler, drier air in place, and hold the warmth to our west. Though this results in continued periods of differential advection with warm advection aloft and cool near the surface - and that can sometimes produce prolific precipitation - the air in the lowest few thousand feet of atmosphere should be too dry to support much precipitation, limiting raindrops to only when the lift and warm surges are greatest, which will correspond to the passage of each vorticity maximum.
So, to put this all together, it looks like tonight (Thursday night) into Friday morning will be the first round of rainfall for southwest New England, but as the rain starts to move east/northeast with the vorticity maximum Friday morning, it will outrun its lower level support, and rain will dissipate to scattered showers, waning in intensity and giving way to leftover clouds in differential advection but a mostly dry Friday afternoon. The next shortwave is on tap for Friday night into Saturday, and this one also should get showers going in southwestern New England, closest to the boundary layer front that will still be stalled to our southwest. Though these clouds may linger on Saturday morning in Eastern New England, these eastern areas should see enough dry advection to break the deck up for some sun during the day. Meanwhile, most of Northern New England stays safely removed from this nonsense to enjoy only intervals of clouds through the period. Still, while eastern Central and Southern New England should find breaks, western locations - including most of CT and Western MA - may be far enough removed from the easterly dry advection...and close enough to the frontal boundary...to maintain saturated low levels and a totally cloudy day. At some point near this wavering front, the collision of airmasses should breed convection, and the backing wind profile should support severe weather near and on the warm side of the front. Right now, on Saturday, that appears to be Long Island to New Jersey, not New England, and even there it's more based on the synoptically favorable that I say this, as there's not a well-defined vorticity maximum overhead, but rather broadscale but still relatively weak cyclonic vorticity advection ahead of the large vort max digging east out of the Great Lakes. Nonetheless, it's an area and time period to watch.
In New England, the battle of dry air from the east and moisture near the front should continue on Sunday, but eventually the ejecting intense energy from the Great Lakes will break down the ridge, driving showers east into New England later Sunday. By Monday and Tuesday, there's lots of disagreement among the guidance, and especially Ensemble members, among what to do with the energy, but the general, rather blurry agreement on the evolution of the system seems to be to take this south and then southeast of New England, spawning perhaps a slow moving coastal reflection to deliver some meaningful precipitation Monday into Tuesday, though timing and intensity will have to wait for increasing agreement in the guidance. Nonetheless, the notion of a slow moving upper low makes sense given that it'll be replacing a rather amplified ridge and steering winds should be rather weak.
Matt
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