Plain-language summary:
After some showers and thunderstorms today, it will clear out with lower humidity tomorrow. However, heat and humidity will quickly surge back in for Monday and Tuesday. A strong cold front will likely bring strong to severe thunderstorms on Tuesday, followed by the first true taste of fall, with the chill being the most pronounced farther northwest with the core of it in northern Ontario. A warm up likely follows for a few days afterwards, with possibly hot weather returning by September standards.
Meteorological discussion:
A weak low pressure in southern Quebec that is bringing showers
and thunderstorms to northern New England today will drag a weak cold front southward
this evening. The front will stall in southern New England, but there will be
clearing and a noticeable drop in humidity to the north. A month ago, a weakening
front like this probably wouldn’t do much, but now cold air masses are growing
stronger with the lower sun angle. Many areas outside urban areas will approach 50F (10C) in the broader valleys and below that in the mountainous cold hollows Saturday night.
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| Source: TropicalTidbits and PivotalWeather |
However, ridging will quickly build across eastern Canada, the
flow will turn to the southwest, and heat and humidity will rebuild. A couple
of very weak disturbances aloft could throw some clouds and complicate
temperature forecasts, but most low-elevation areas will reach 86F (30C) or
higher on Monday, and from southern Quebec eastward, on Tuesday as well. A low
pressure will strengthen and move northeastward into Hudson Bay and then
northern Quebec on Tuesday, leading to breezy southerly or southwesterly winds,
especially where wind can channel, such as the St. Lawrence and Champlain
Valleys. The low pressure will also push a strong cold front eastward, and
depending on the orientation and timing of the front, could lead to strong to
severe thunderstorms given the heat and humidity.
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| Source: TropicalTidbits |
The much cooler air mass will only slowly move in, facing
resistance from the East Coast ridge and the incredibly warm ocean temperatures
off the East Coast. Combined with the upper-level trough positioned to the west
and more westerly instead of northerly flow, the cool air mass will modify as
it moves eastward, and northern/western Ontario will likely get the core of the
cool air. Still, it will be the beginning of September then, and it will provide
the first true taste of fall, with the most pronounced cooling over Ontario.
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| Source: TropicalTidbits |
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| Source: NOAA |
However, there are signs that there will be another warm up
to possibly hot temperatures a few days afterward, but by then, it becomes
increasingly difficult to sustain hot weather. Also, the mean ridge could be over central North America, which tends to lead to “sneaky” cold
fronts bringing cooler air from the north especially over eastern New England, though this could be counteracted by potential hurricane in the southwestern Atlantic pumping heat northward.
However, this is still quite far out.
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| Source: TropicalTidbits |