Showery and cool today and Monday; warmer and drier for a few days afterward, then thunderstorms Friday and somewhat cooler again next weekend; possible first heatwave afterward

Plain-language summary:

It will be rather cool and unsettled today and tomorrow due to a cool pool of air aloft directly over us. After a steady light rain from southern Vermont to southern Maine this morning, it will partially clear out with scattered convective showers this afternoon and evening. Showers will mostly dissipate tonight before some more form mostly along and northwest of the Appalachians tomorrow before drying and clearing out everywhere tomorrow night, leading to a cooler night. However, sunshine and a warming air mass will lead to quickly warming temperatures through Friday, before a cold front brings thunderstorms on Friday and cooler temperatures again next weekend. However, next weekend will not be a repeat of this weekend, as it will still be rather clear and dry and also not as cool as this weekend. It will likely heat up for the following week, with us possibly experiencing the first real heatwave of the summer.

Meteorological discussion:

A broad upper-level low slowly moving eastward through our region is making for a cool and showery weekend for most. A disturbance rotating around the upper-level low is bringing steadier light rain to southern Vermont to southern Maine this morning. Then, there will be some clearing and periods of sunshine, but with the cold air aloft, that will lead to instability, leading to scattered convective showers across the region this afternoon and evening. The showers will mostly dissipate with the loss of daytime heating tonight. Despite the overall cool air mass, the residual clouds, wind, and low-level moisture will lead to overnight temperatures still slightly above average tonight. Another subtle disturbance will shift the winds from westerly to northwesterly Monday afternoon, leading to some more showers (especially along and northwest of the Appalachians with upslope enhancement, with little rain southeast of the Appalachians due to downsloping) and a more direct shot of cooler and drier air. Ahead of this reinforcing shot of cooler air, from Vermont and southern Quebec on eastward, temperatures will be similar to or slightly warmer than today, while west of there, especially over eastern Ontario, it will be quite chilly for June, generally below 60F (16C) even in the afternoon. With fewer clouds and drier air, as well as high pressure approaching our region, Monday night will be cooler for most of the region.

 

Source: TropicalTidbits

Source: TropicalTidbits

The high pressure will take over our region for the middle of the week, leading to more sunshine and temperatures quickly warming back to above average in the region as the strong June sun modifies the cool air mass, and winds calm down and then shift to southwesterly, promoting weak warm advection. By Friday, another low pressure will move into central/northern Quebec, bringing a cold front into our region. The lack of strong ridging building in beforehand will limit how hot it gets, with temperatures of 86F (30C) or higher being unlikely next week. Nonetheless, it will get warm and humid enough for thunderstorms to erupt along the cold front, with some of them possibly being strong, as they often are in summer.

 

Source: TropicalTidbits

Behind the cold front, a cooler, drier air mass will follow associated with a cool Canadian high pressure, though with sunshine, temperatures will only be slightly below average. With the NAO turning to near neutral, systems will be moving faster, and there does not appear to be another slow-moving upper-level low to produce days of cool, showery weather like this weekend. Instead, the Canadian high pressure will move southeastward into our region and then to the south east by the following week, leading to a quick modification of the cool air mass in the June sunshine as the cool northwesterly flow stops and then switches to a warm southwesterly flow. In addition, the PNA will be turning slightly negative in association with an upper-level trough entering the Pacific Northwest, a reversal from the strong ridging this weekend. That will also trigger an upper-level ridge to build over the eastern U.S., likely bringing the first big widespread heat wave of the summer. It remains to be seen exactly who gets the core of it (perhaps more likely just to the southwest over the Midwest U.S. and Great Lakes regions) and how intense it is, but it appears likely that there will be at least a few hot to very days in our region, particularly on days with strong westerly flow right ahead of a cold front. A surge of tropical moisture and convection into the Gulf of Mexico and Deep South of the United States associated with a tropical wave or possibly even an organized tropical storm will also release a lot of latent heat into the environment and spread it into the eastern U.S., where the heated air sinks, amplifying the ridge and heat wave. However, it's also possible that most of the heat centers to our west, with eastern New England especially avoiding most of the heat with backdoor cold fronts and southeasterly flow off the still cool Atlantic waters just offshore. Another possibility is that the tropical moisture manages to track northward into our region, leading to very high humidity but more clouds and rain, leading to lower temperatures, especially during daytime.

Source: Climate Prediction Center

Source: TropicalTidbits