Plain-language summary:
Somewhat similar to at the end of May, a strong heat wave baking the central, southern, and Midwest U.S. will largely fail to reach northern New England and southeastern Canada. It will briefly turn moderately hot and humid in western areas on Thursday and in southern Maine on Friday, but with maritime moderation. Some showers and thunderstorms will occur on Friday, but very little if any severe thunderstorms are expected. An unseasonably cool air mass will settle in for the weekend and early next week, especially in eastern areas which will be cloudier and have showers. Some warming is expected next week but the core of the heat will likely still stay to the west.
Meteorological discussion:
After the hot spell in mid-May, real summer heat has been largely absent. This week, a strong ridge is building over the southern and midwestern U.S., but a persistent trough over Atlantic Canada will lead to northwest flow aloft. The air mass is not particularly cool, and areas with sunshine will actually have slightly above average highs today and tomorrow, though with low humidity.
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| Source: PivotalWeather |
However, somewhat similar to at the end of May, the northwest flow will cause the warm front to slow its progression northeastward. At the same time, surface high pressure moving just offshore will be far enough north for the low-level flow to be more southerly or southeasterly off the still cool Atlantic shelf waters, moderating the hot air mass that is trying to slowly move in from the southwest. The hot and humid air mass will be forced above the cooler, low-level air, causing clouds and showers to form on Thursday, further reducing the potential for hot weather. Southeastern Ontario and northwestern New York could be the exception, where temperatures could reach 86-90F (30-32C) in some spots, as that region is the farthest from the Atlantic and will receive some downsloping from the southerly flow off the Adirondacks.
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| Source: TropicalTidBits |
Meanwhile, an upper-level low over central Canada will dive southeastward, dragging a cold front on Friday which will suppress the hot air to the south, though southern Maine may get rather hot with downsloping westerly flow right ahead of the front. The front won't be particularly well defined, with it being more like a large area of cold advection. With some daytime heating, showers and thunderstorms will form in the afternoon, but there will not be that much instability with the humidity already pushed to the south, and the best dynamics will be off to the north and east. So few if any severe thunderstorms are expected.
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| Source: PivotalWeather |
By Saturday, everyone becomes unseasonably chilly as the trough deepens over eastern New England. Northern New Hampshire, western Maine, and the Eastern Townships of Quebec could fail to reach 59F (15C) on Saturday with brisk northwesterly flow, cloudy skies, and some showers. The upper-level low will slowly move eastward and out of the area, leading to a sunnier but still cool Sunday, except Maine which will still be cloudy and even cooler.
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| Source: TropicalTidBits |
The upper-level pattern this weekend will almost resemble an Omega block, which is a relatively stable, slow-moving weather pattern. However, unlike some model forecasts a few days ago showing the upper-level low stalling and producing record cold temperatures, it now appears likely that the system will slowly move out and be completely out by Tuesday. Normally, substantial warming would take place as this occurs, but the northwest flow aloft looks persistent and could block any real surge of heat trying to come in from the southwest once again. Areas that get stuck in the warm front would have rain and more unseasonably cool daytime temperatures. However, as we approach the peak of summer, the cold air masses and upper-level troughs over eastern Canada typically weaken, which will probably allow some of the heat to eventually reach our area, perhaps at the end of June or in July.
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| Source: TropicalTidBits |
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