Plain-language summary:
Although it will be warm to hot for most on Monday, a strong cold front coming from the northeast will dramatically cool temperatures down Monday night across Maine and the Eastern Townships of Quebec and then all the way to southern New England and eastern Ontario by Tuesday night. The heat will attempt to surge back on Wednesday, but the wind will not be in the ideal direction to do so, and clouds, showers, and thunderstorms will limit heating ahead of the "main" cold front approaching from the west. Temperatures appear to be near to slightly below average for the rest of the week.
Meteorological discussion:
Ridging starts building in today, with mostly sunny and warmer conditions for most. Humidity will be relatively low, but it will increase as southwesterly flow advects hotter and more humid air by Monday. However, this ridge is weaker and more suppressed to the south, with a strong, cold upper-level low over Labrador bring closer than models had shown earlier, shown in the model trend loop below:
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| Source: TropicalTidBits |
Because of this change, the heat wave that was originally expected to occur will not occur, except perhaps in far southwestern areas. It will be warm or hot for most of us on Monday, as a front stalls just to the north, except in northern Maine where it will be cloudy.
However, after a subtle, elongated low pressure passes along the front in the evening, a strong back-door cold front will push southwestward, and temperatures will actually be below average on Tuesday northeast of the Green Mountains and in southern Quebec. Temperatures will drop sharply in many areas as the front passes, especially in eastern New England, as winds change from westerly to northeasterly and low-level clouds move in. In Maine and the Eastern Townships of Quebec, it could be below 50F (10C) for most of the day, an impressive feat for the last day of May! It will still be hot in southern Vermont and southern Adirondacks before the cold front pushes southward and westward, eventually down to eastern Pennsylvania by later in the night.
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| Source: TropicalTidBits |
The cold air mass will lose its intensity and its core will pass to the east, and southerly flow will return by Wednesday. However, this flow is still incorporating influence from the still cold Atlantic Ocean, and warm, moist advection will lead to clouds and showers, preventing a dramatic warmup. The hot air mass will continued to get squeezed by a cold front approaching from the west and a cool maritime air mass to the east.
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| Source: TropicalTidBits |
The cold front combined with a little daytime heating ahead of it will generate showers and thunderstorms in the early afternoon over northern New York and moving towards Maine by late evening. Some of the thunderstorms could be severe in far southwestern areas, but areas to the northeast will be too stable with the cooler maritime air at low-levels.
After the cold front, no more heat is expected for a while, with a strong and cold upper-level low over central Canada dominating for the second half of next week. Our region will be well to the east of there and so will not get the full force of the cold air mass, but it will still be cooler than average on most days. Interestingly, this would make it the 7th year out of the last 8 which featured a cool early June, with last year being the big exception. Our position to the east of the upper-level low combined with the June sun angle is also favorable for rounds of showers and thunderstorms, more due to colder air aloft than true low-level heat and humidity.
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| Source: TropicalTidBits |