Plain-language summary:
Today, it will be warm and humid with scattered showers and thunderstorms, some severe and mostly southeast of the U.S./Canada border. It will then be mostly sunny and dry from Monday through Wednesday, except some more clouds and maybe a few showers north of the U.S./Canada border on Wednesday; this marks the longest dry stretch for most since before last week's heat wave. Widely scattered showers and thunderstorms with moderate heat and humidity are expected from Thursday through next weekend, though there will be subtle day-to-day variations that are still uncertain. While extreme heat is unlikely in the foreseeable future, that could be the start of an extended period of (at least moderate) heat and humidity.
Meteorological discussion:
It has been an amazingly wet period since last week's heat wave ended, with rain almost every day in some areas! We will have one more wet day today for many, as warmth and humidity has briefly surged in right ahead of a potent cold front plowing through eastern Ontario and southern Quebec this afternoon. With the daytime instability, scattered severe thunderstorms will fire ahead of the cold front, especially along and southeast of the Appalachians, where the storms will arrive the latest and therefore it will the hottest before the storms form. However, unlike yesterday, dry air aloft is keeping skies relatively clear and sunny outside the storms, not everyone will get rain, and the rain will only be in brief thunderstorms.
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| Source: TropicalTidbits, Aviation Weather Center, and Storm Prediction Center |
A cool Canadian high pressure moves in tomorrow, though the air mass is not as cool as the one earlier this week and will quickly modify with abundant sunshine, a rarity in recent days. With a much weaker temperature gradient and associated jet stream, the high pressure will only slowly move eastward through Wednesday, assuring sunshine and warming temperatures for most until then, though areas north of the U.S./Canada border will see more clouds (possibly even showers) and be cooler on Wednesday due to closer proximity to a low pressure moving into central Quebec then. This will mark the longest dry stretch for most since before the heat wave. The low pressure will drag a weak cold front through our region Wednesday night into Thursday, possibly sparking scattered thunderstorms, but with most of the dynamics going to the north and lack of any strong trough pushing in, widespread heavy thunderstorms are not expected. In some areas, it could actually be hotter on Thursday than on Wednesday, especially east of the Appalachians, with slight descent from weak cold advection, downsloping westerly flow, and the lack of direct northerly flow to usher in any real cool air mass. The upper-level ridge will mostly remain just to the south for the rest of the week, keeping most of the heat down there (where it has also been much drier, allowing the sun's energy to go into heating the ground more than up here). However, we will likely still see surges of moderate heat and humidity ahead of any likely weak cold fronts and upper-level troughs to the west, and northern areas will likely see the hottest temperatures since last week's heat wave. Daily specifics are hard to tell now due to the dependence on subtle disturbances producing areas of clouds and showers that will be hard to predict until a few days in advance.
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| Source: TropicalTidbits |
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| Source: TropicalTidbits |
Beyond next week, models interestingly show ridging expanding across most of the U.S. and southern Canada, bringing hotter than average temperatures from the West Coast to the East Coast, which goes against the usual cool West/warm East or warm West/cool East regime. However, this might be plausible due to the positive NAO and AO preventing any high-amplitude troughs from ushering in arctic air into the contiguous U.S., and the climatological retreat of the jet stream northward into Canada going into mid-summer, allowing heat and ridging to dominate most of the contiguous U.S. Given how wet it has been, it is unlikely to turn super hot right away in our region, but if ridging can persist in our region, and the rains remain less persistent starting next week, then we could be seeing real heatwaves by mid-July.
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