Cool and unsettled week ahead, especially Tuesday and Wednesday and from Vermont eastward; still no true soaking rain except for Maine; gradually turns warmer and drier afterward with uncertainty for the following week

Plain-language summary:

After record heat on Thursday and Friday, the following week will be rather cool, especially from Vermont on eastward. The weather pattern will be unusually slow-moving, with a slow-moving but weakening storm bringing cloudy and showery weather at times, especially Tuesday and Wednesday, but there will still not be a true soaking rain except for Maine. It will gradually warm up and dry out for the rest of the week, but there is uncertainty in whether the warming trend will continue into the following week.

Meteorological discussion:

The ridge that brought the record heat on Thursday and Friday retrograded westward to western and central Canada, allowing a trough to take over Quebec and Atlantic Canada with an associated strong backdoor cold front over the weekend, with temperatures in eastern New England dropping 40-50F (21-28C)! New Hampshire and Maine will continue to be the coolest for a while, as a cool air mass from the north combines with a maritime air mass off the Gulf of Maine, producing low clouds and rain, preventing the sun from warming the already cool air mass. They will also be the closest to a low-pressure system over Nova Scotia that will only slowly move due to the -NAO and corresponding Greenland blocking. West of the Green Mountains, it will be progressively sunnier and warmer the farther west you go, with eastern Ontario experiencing temperatures close to the climatological average.

Source: TropicalTidbits

Source: Climate Prediction Center

It will temporarily turn warmer on Monday ahead of another upper-level disturbance and cold front approaching from the northwest and as the storm in Nova Scotia slowly pulls off to the east. It will still be cool in Maine due to the lingering clouds and influence from that storm. However, the upper-level disturbance diving southeastward will interact with the storm in Nova Scotia on Tuesday and combine into one broad, vertically stacked storm over eastern New Brunswick that will move even slower and actually stall until late Wednesday before weakening and then slowly moving eastward. The blocking pattern associated with the -NAO and the ridge in western Canada associated with the +PNA are major contributors to this pattern. Initially, steady rain and extremely cool temperatures for June (perhaps highs below 50F or 10C) will dominate in Maine and perhaps the Eastern Townships of Quebec. Clouds and scattered showers will spread to eastern Ontario and the Adirondacks, especially on Wednesday, but there, occasional breaks of sun will lead to temperatures still being cool but not as cool. As the storm weakens and slowly pulls away after Wednesday, it will gradually warm up everywhere with temperatures likely returning to near the climatological average by early the following week.

Source: TropicalTidbits

Source: TropicalTidbits

The slow-moving vertically stacked storm to the east will cause persistent mid to upper-level northerly flow to bring smoke from numerous wildfires in central/northern Quebec all the way down to the mid-Atlantic U.S., even near the surface, causing degraded air quality! This will be especially true west of the Green Mountains, which is more in the direct path of the smoke and will receive less rain to dissipate the smoke. Maine appears to largely escape the smoke, with any smoke reaching there being dissipated by rain. The smoke will likely persist until the storm moves out over the weekend, with more W/WSW flow allowing smoke to stay well to our northeast by then.

Afterwards, different models and model runs diverge on the pattern evolution. Some suggestions are for the ridge in western Canada and blocking pattern to weaken (PNA decreasing and NAO increasing), allowing hotter and eventually more humid air to overspread from the southwest more frequently. Other suggestions are for another upper-level disturbance to dive southeastward into Atlantic Canada, prolonging the trough and reinforcing the cool weather. However, there is still little indication of a widespread soaking rain, which could allow drought conditions to develop given the lack of rain for the past month. Dry ground allows more of the Sun’s energy to go into heating the ground instead of evaporating moisture, which is especially important at this time of year with the high sun angle. This could allow at least daytime temperatures to be near the climatological average even if some upper-level troughing lingers, or even above average if the upper-level troughing goes away more quickly.

Source: TropicalTidbits