The short term is fairly straight-forward with dry air throughout the atmospheric column producing lots of sun, and winds light beneath surface ridge axis. As the ridge has started to nudge east of New England, winds have slowly come to blow out of the south, but ocean-land interaction has a well-defined sea breeze circulation underway. The key to coastal temps was nailing the pinnacle of morning rise before the sea breeze would kick in, because the water/air combination are cool enough to keep sea breezed locations in the 50s thru the afternoon once the cycle sets up, and this cycle may get strong enough to drive cool air through about 20 miles of the coast! Elsewhere, the temperature rise has been unusually slow, but that hasn't been surprising given the limited vertical mixing of the boundary layer owing to a subsidence inversion beneath the ridge axis.
This evening should be fantastic through the interior as a light south wind eventually teams up with late evening cirrus blanket moving east out of NY State to keep temps up, while coastal locales through most of ME will find the coolest temperatures thanks to longest lasting mostly clear skies (especially in ME) and more importantly the cool, marine air near the coasts. Of course, the clouds coming in are in advance of the cold front marching across the Great Lakes that will be pressing through New England on Thursday. This front has been active diurnally, with convection evident along the boundary again today, though the larger band of convective and stratiform processes ahead of the front are coming with the combination of a moist theta-e tongue in the lower levels, and height falls with vorticity maximums riding in the west-southwest flow in the mid-levels. This band of showers will lose some intensity Thursday night over New York State as the theta-e tongue is muted by its encounter with the dry and cool air in place over the Northeast. Still, a few scattered and light showers should survive the trip into VT and Western MA early to mid morning Thursday. As has been mentioned here the past few days, I think the amount of altocumulus/altostratus will be rather significant, and this should limit diurnal temperature rise. NMM surface temperature forecast is warmer than today in Eastern New England, which makes sense for the coastal locales given absence of sea breeze (except coastal Maine and south facing coasts), but I think the implication of 70s for all of Eastern 2/3 of MA is overdone. I have to say, though, that it's with only low to moderate confidence that I make that statement, because the other thing I've been pointing out in these discussions for Thursday is that, technically, the warmest airmass *is* in place ahead of the front with the strengthening southerly wind...I just think the presence of clouds through most of the column in most of New England means we can make 60s widespread...but 70s should be more localized to places where breaks of dim sun are seen the most.
The surface cold front will be an important feature in the forecast for Friday, as the front will continue slowing on its progression through New England, reaching the waters south of New England Thursday night where it will stall in response both to rising heights in the mid-levels (shortwave ridging) in advance of a stronger shortwave digging from the Central Great Lakes and Ohio Valley to the Northeast and Mid-Atlantic coastlines on Friday. This shortwave ridging not only stalls the cold front, but also means Friday should start dry in New England, ahead of the surface reflection of the aforementioned upper level disturbance. That surface reflection will be a steadily strengthening low pressure center ejecting from the Tennessee River Valley and moving northeast off the NJ coast and south of New England Friday through Friday night.
The details of this event are still up for grabs, as we do have some similarities to this past Friday evening/night event...billed to be a heavy rain maker but in reality taking most of the rain south of New England as a flat wave. While this Friday's event has similarities of being a flat and rather progressive surface wave resulting from what is perhaps the most important similarity - channeled vorticity - there are differences in the evolution of the upper level pattern over the weekend. Let's start with the channeled vorticity thought - Dave Eichorn, the Chief Meteorologist at WSYR in Syracuse, used to share with me when I worked there that some of the biggest blown forecasts he'd experienced and seen came from giving too much credit to channeled vorticity, or a vorticity maximum that has a relatively small area of cyclonic vorticity advection ahead of it. Putting this in simpler terms, what he was saying is that it doesn't always matter that an energetic disturbance is strong, or elongated, or impressive to look at. What matters is the angle at which that energy is coming in. It's a basic concept that any meteorologist learns - the strongest lifted air favoring clouds and precipitation comes from a perpendicular face of vorticity to the mean wind flow - but can easily be forgotten in the heat of battle. This was a big part of last Friday's failed rain forecast, and I see a similar potential evolution this time around. The difference with this Friday night's event is that the stakes are higher because the surface baroclinicity (temperature difference along the front) is stronger and closer to New England, so the storm will strengthen quicker in the game, even though the end product isn't as impressive as last week's stacked low in extreme Eastern Canada.
Of course, the longwave pattern is important here, too, and remember the thinking from early this week that the wavelengths in North America aren't matching up, and this storm is really going to deepen and probably persist as it's forming in a necessary effort to bring atmospheric equilibrium (if I just lost you, read the discussion from Monday). This means the upper low will eventually end up stalled over Southeast Canada and New England, posing different challenges later this weekend than what we saw a week ago.
So, the bottom line here is that I'm banking on a shot of rain and wind for Southern New England later Friday after a dry and perhaps partly sunny start, with the heaviest precipitation coming through Friday night ahead of the surface reflection of low pressure. I'm indicating the heaviest rain should shift to Northern New England on Saturday in my on-air forecasts, but review of the latest data shows the upper low may actually expand east too fast to allow good warm air advection into Northern New England on Saturday, meaning the heaviest rain may fall over the Gulf of ME and Nova Scotia but this will have to be re-examined...is my gut on this for now though.
Convective potential Saturday in Western New England beneath the cool pool, then for all of New England on Sunday, but downsloping flow and occluded mild air in at least southern new england on Saturday should allow mild and windy conditions before cold air moves in Sunday with possible flakes in the mountaintops or at least graupel beneath convective bursts!
Matt
