On the "surface" (pun intended!) it's more of the same today - only a fraction of you reading compared to the normal daily average, so a sincere thanks for stopping by, especially since there's still plenty of weather to challenge forecasters into and through the upcoming weekend.
In the short range, why restate the obvious? Not much has changed from yesterday with respect to fire danger, which continues to build thanks to gradually rising temperatures but a lack of moisture. In fact, early morning temperatures dipped into the lower 40s and even some 30s as far south as Northern Florida! This should serve as evidence to just how penetrating this dry airmass has been, and how little moisture is really available, even with a south and eventually southwest wind taking over. So, by driving the temperature up, all we do is drive the relative humidity down more, and this has created the dry fuel we looked at yesterday. An updated fire danger class map can be found here. 
Also worth noting that air quality forecasts are for moderate in the urban areas of Southern New England, but this doesn't really correlate well with the atmospheric setup, which still features deep mixing through all of New England, except at the coastlines but there we have an active sea breeze. So, even though winds are light, air quality really shouldn't be all that bad given these parameters, and real-time monitoring systems indicate mostly low particulate, and extremely low ozone, levels. The only way I could really see that worsening is with limited mixing, or advection of polluted air into New England, neither of which is likely.
The ocean storm off the coast is really impressive on a number of levels. Convective clusters firing around its center have been showing impressive cool cloud tops to as cold as -55 and -60 Celsius in stronger bursts of thunderstorms. Quikscat satellite derived wind estimates are in excess of 50 knots, as shown in this image. 
The storm is gone on Friday and airmass modification continues. Weak warm advection has been gradually bleeding a warmer air into New England, and even with dry air and mostly clear skies with light wind in a lot of spots, Thursday night will be milder than previous nights thanks to the warmer airmass moving in. Slightly higher pedestal to build from will also help Friday's high temperatures to recover nicely, and though 850 mb temperatures would support widespread 75 to 80 in Southern New England, and I do expect good mixing, I don't think the mixing will be quite that deep and I prefer 925 mb temps as guidance instead. This gives almost all of New England highs squarely in the 70s, with warmest spots coming within a degree or three of 80. Cold front sagging south puts the brakes on at the Canadian border for a time, but moves south through Northern ME with cool air surging south and temps in places like Aroostook County, ME, dropping from the 60s to 40s in only a few hours Friday afternoon. This type of change should be an indication of what's to come for the remainder of New England.
I make that last statement because high pressure will be sliding east across Quebec while strengthening Friday night through Saturday, and this will launch the cool air farther south as a rather well defined back door cold front. The real challenge is determining how quickly and with what intensity the front backs in. This time of the year, it's VERY easy to slide a front like this over the ocean, because water temps are about equal to the air that's coming in, so there's really no displacement that has to take place. Therefore, not long after the front reaches the Maine coast, you can take the eastern end of the front and swing it south, bringing it into Eastern MA. So, by 12Z this is probably into Cape Ann and the South Shore of MA, then across most of the I-95 corridor by 18Z. The backdoor front is actually so wrapped up, though, that rather than a northeast wind, it's an east and southeast wind that tries to take over. This will bring cooler air, but not necessarily a lot of clouds. For now, seems wise to put highs in the 50s through ME on Saturday, in the cool air, 60s with immediate coastal 50s in Eastern MA, and reserve the warmth for Central and Western New England, where highs may hit 80! Given the surface convergence along the front, the lifted index dropping to 0 and CAPE values of a few hundred jewels per kilogram, tendency is to put thunder in, and I did that for Saturday afternoon on the warm side of the front. Upon further evaluation, though, I'm not sure the guidance are accurately forecasting dewpoints (50s...where does that come from?), so that thunderstorm threat could probably come out of the forecast. In the warm air, bounday later temps are warm enough to support around 80!
We all transition to the cool air for Sunday, but the southeast rather than northeast wind implies not a raw overcast so much as a cool blend, but mid level warm advection may make up for that by pushing clouds back in over the top of the surface front on Sunday, keeping narrow warm advection rain band on New York State before bringing it slowly into New England on Monday. As mentioned yesterday, Monday may still bring enough dry advection to Eastern New England from the Maritimes high to result in showers losing a lot of liquid on the eastward trip across New England, with higher amounts found west, and the 12Z GFS appears to be picking up very well on this solution. It takes until the middle of next week to get warmth successfully back in ahead of a weakening cold front moving out of the Great Lakes.
Matt
What a plseaure to meet someone who thinks so clearly
Posted by: Miles | Thursday, April 26, 2012 at 03:03 PM