After an extended period of clouds and showers, the culprit front is settling farther south of New England, taking the feed of Gulf of Mexico moisture slowly southward with it. The moisture is being replaced by dry and cool autumn air, streaming southward as an area of high pressure - fair weather - muscles its way southward across Ontario and Quebec, and close to the U.S border with Canada, eventually set to pass over North-Central Maine late Thursday night. The feed of tropical moisture, however, will still be established from the Southeast to the Mid-Atlantic and Appalachian Mountains, and will be ready to return to New England soon enough.
For now, though, the drier air pushing southward has been resulting in a very sharp line of clearing moving from northwest to southeast, and as sprinkles diminish on the South Coast, clearing follows, but will arrive to these South Coastal areas last, perhaps not until just prior to sunset for some. Nonetheless, temperatures will be relatively uniform across all six states, largely because those areas farther north with the longest duration of sunshine today are sitting more squarely in cool Canadian air, while those in milder air have remained under lingering cloud cover, thereby bringing almost all communities into the upper 50s and lower 60s with somewhat cooler temperatures deeper into the cool air at the Canadian border. Winds will remain light from the northwest across northern New England and the northeast in Southern New England, and will diminish Thursday evening. These conditions bode well for Game Two of the World Series at Fenway Park, with clear skies, a light wind blowing in from right-center field and temperatures either side of 50 - no problem for the Sox, who played in similar temperatures and conditions in Game 2 of the 2004 World Series, but chilly for fans sitting in the stands! As for the full moon this evening, it's a special one and runs parallel to the recent role of full moons in pivotal Red Sox games - check out my main page for more on tonight's special full moon!
By predawn Friday morning, temperatures will have dipped into the 30s in many communities across New England, resulting in many areas of frost, though urban areas of Southern New England and those near the South Coast will hang in the lower 40s. This cool start will rebound with the help of sunshine early Friday, though the atmosphere will be in a state of change. At the surface, change will be slow as high pressure slides east of New England and over the Scotian Slope - the waters south of Nova Scotia - and wind flow remains out of the east...and slowly turning to blow from the southeast...keeping any rapid warmup from making its way into New England. Aloft, however, the wind will blow from the south and southwest between a storm crossing the Midwest and the high pressure to our east, and this will tap air from the Appalachian Mountains and Mid-Atlantic, carrying it into New England later Friday. Remember what's found to our south - the very same Gulf of Mexico moisture we just sent southward today! The key player in holding this moisture in place just to our south, and keeping it available to return, is a large upper level storm over Mississippi - it's been in place for a couple of days and is the same disturbance looked at in this discussion over the past few days. As long as the upper level system sits over the southeast and swirls counter-clockwise, it's going to continue sending a feed of moisture northward through the Eastern United States.
Once our dome of high pressure begins to move east of New England, this warm and moist southern air will be allowed to spill north, and clouds will increase after morning sunshine on Friday. The more substantial surge of warmth and moisture follows on Friday evening and night with a resultant swath of rain moving from southwest to northeast across New England, with most areas picking up half an inch to an inch of rain, and some of Western New England receiving closer to an inch and a half in localized bands where terrain enhances precipitation in the Berkshires and Green Mountains. This moisture will leave behind morning clouds and fog, but a mild southerly flow early Saturday. As Saturday wears on, the showers marking the leading edge to warmer air will stall across Northern New England early, holding clouds across the North but likely allowing some sun to break through in Southern and Central New England. With a strengthening southerly wind flow, temperatures should rise into the 60s for most of these areas, though 70s are a distinct possibility in Southern New England where the sun makes it greatest appearance and enough mild air will be in place. As the upper level disturbance dislodges from the Southeastern U.S., however, and moves across the Northeast, a chunk of it's energy will be strung out before swinging across New England, likely resulting in heavy rain Saturday for New York State, then carrying thunderstorms and downpours into New England from west to east Saturday afternoon, evening and night. By Sunday, cooler air will filter into New England, though at least some clouds are likely to bubble up in this new air, and the clouds may outweigh sunshine through the day with the combination of not only cooler air, but also moisture left behind from the upper level disturbance that was chock full of tropical air originally. In fact, as a strengthening storm center wraps from Lake Ontario into Central Quebec, it will tap a source of deep cool air out of Hudson Bay, Canada, and sent it sailing southward. The leading edge to this new air - a reinforcing cold front, if you will - will bring a Sunday afternoon shower to Northern and Western New England, and the hilly terrain of Central New England.
Behind Sunday's disturbance, the flood gates for cool air will open, and a shot of below normal air will spill into New England, bringing sunshine but holding high temperatures only in the lower 50s, on average, for Monday, with the higher terrain of Northern and Western New England holding in the 40s! This pattern of cool daytime highs and chilly overnight lows will return in surges every few days for the next couple of weeks, it seems, as a jet stream trough will remain carved out across the Northeast...allowing for swings in temperature between below and near normal values.
Technical Discussion: Time has been quite limited as of late...none for today.
Matt
