Plain-language summary:
It will be hot and humid through Thursday, hottest on Wednesday for most, as we are in the climatological peak of summer. With the heat and humidity, each day has a chance of isolated thunderstorms at least over higher terrain, with more widespread showers and thunderstorms today into Monday and Thursday into Friday. It turns cooler and drier next weekend, with likely alternating periods of modest heat and humidity and cooler, drier air masses afterward.
Meteorological discussion:
Hot and humid through Thursday with showers and thunderstorms today into Monday
We are now in the dog days of summer, the climatological peak for temperatures in the region. It is indeed hot and humid across the region, aided by a -PNA and associated upper-level trough in the western U.S. and ridge in the eastern U.S. Although it is not record hot, it will be persistently hot through Thursday (and southeast of the Appalachians, possibly Friday), with the chance of at least isolated thunderstorms each day with the heat and humidity, especially over higher terrain. One exception will be coastal Maine today, where the southerly wind off the chilly Gulf of Maine will cause clouds and much cooler temperatures, like many days earlier this week. A weak disturbance will trigger more widespread showers and thunderstorms today in eastern Ontario and southern Quebec, gradually shifting into northern New England tonight into tomorrow, though the cool, stable air in Maine may prevent thunderstorms there. The lack of strong dynamics should preclude widespread severe thunderstorms. The clouds and rain will make tomorrow slightly cloudier and cooler for northern New England, but it will still be very humid. The disturbance will have moved far enough east Wednesday will likely be the hottest day for most, with temperatures exceeding 90F (32C) in many lower elevation locations away from the Atlantic Ocean. Although the cold front won't arrive until Thursday night into Friday, increasing clouds and perhaps scattered thunderstorms on Thursday will likely keep temperatures slightly lower that day.
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| Source: Aviation Weather Center |
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| Source: TropicalTidbits |
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| Source: TropicalTidbits |
Showers and thunderstorms late Thursday into Friday, then more frequent cooler air masses but still hot and humid at times
A low-pressure system pushing into central Quebec on Thursday will bring a cold front into the region, likely triggering more widespread showers and thunderstorms, but it remains unclear if any of them will turn severe. The cold frontal passage will occur Thursday night into Friday, though increasing instability, deeper moisture, and falling upper-level heights could already lead to more thunderstorms on Thursday well ahead of the cold front. The cold front will end the prolonged stretch of heat and humidity, though it might only turn slightly cooler than average if the push of cool air weakens as it approaches our region. July is the month in which these cool air masses tend to be the weakest. Still, with the PNA turning neutral to slightly positive, favoring at least some upper-level ridging in western North America, combined with the NAO turning slightly negative, it appears likely that there will be enough troughing at least occasionally in eastern North America to provide cold fronts and cooler, drier air masses on a regular basis starting late next week and continuing into the following week, preventing any prolonged heat wave, though it could still get quite hot and humid ahead of any cold fronts, as it is July. It also appears unlikely for there to be sustained cool temperatures.
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