Scattered showers and possibly a thunderstorm today mostly in western areas; cool, mostly cloudy, and showery Monday before warm or mildly hot and mostly sunny through Friday, though with possible scattered showers over terrain; likely storm next weekend but with to-be Ernesto likely staying offshore; then brief cooldown before turning warmer but not excessively hot for a while

Plain-language summary:

 

It has mostly dried out after Debby's heavy (in some places historic) rainfall on Friday. Some scattered showers and possibly a thunderstorm are expected today mostly in western areas, with seasonably warm temperatures in eastern areas and cool temperatures in western areas. After a cool, cloudy, and showery Monday, it will turn hotter, drier, and mostly sunny, but not particularly hot, with scattered afternoon and evening showers mostly over higher terrain still possible. A storm will likely bring more rain next weekend, with some timing uncertainty, but to-be tropical storm or hurricane Ernesto will very likely pass to our southeast and not bring direct impacts to our area. It may temporarily turn cooler and drier afterward before a stretch of mildly or moderately hot late-summer weather takes hold.

Meteorological discussion:

The remnants of Debby that were initially expected to likely stay to our south ended up bringing heavy rain to most of our region on Friday, even record rainfall of up to 8" (200 mm) in just 24 hours in southern Quebec, even with its very fast movement. The trough over the Midwest U.S. ended up bring deeper and farther east than earlier expected and was therefore able to pick up Debby and swing it well to the north into Quebec.

 

Source: CoCoRaHS

Source: TropicalTidbits

 

 

Debby is long gone, with the upper-level trough that directed Debby into our region now slowly moving in. The cold air aloft along with relatively warm surface will lead to some instability, leading to scattered showers and possibly even a thunderstorm, especially west of the Green Mountains, with areas east of the Appalachians being farther from the upper-level low still being mostly dry. Temperatures will still be close to average east of the Appalachians, but will be rather cool in eastern Ontario, closer to the upper-level low center. Tomorrow will be the coolest day for most of us, failing to get much above 70F (21C) even in lower elevations, as the upper-level low moves directly over northern New England. It will also be rather cloudy and showery.

 

Source: TropicalTidbits

Starting Tuesday, a very broad though weak surface high pressure will dominate in southeastern Canada, New England, and Midwest U.S. The upper-level ridge in northwestern Canada that has led to record heat there for the past few days will slowly move into central and northern Quebec by mid-week, leading to slowly warming temperatures. However, the August sun is a little weaker, and with weak northerly flow not accessing any of the truly hot air from the west, it will not get hot quickly, with temperatures reaching only slightly above average. As the high pressure eventually moves off the East Coast by Friday, weak southerly flow could finally lead to it being a little hotter, but that depends on the timing of another likely cut-off low moving in from the Great Lakes that will likely bring more rain, perhaps heavy rain next weekend, and the timing of such slow-moving systems always has high uncertainty, perhaps by a day or more. However, it looks rather dry from Tuesday through Friday, though scattered afternoon and evening showers during peak daytime instability are possible, especially over elevated terrain, with the strongest ridging located just to the north.

 

Source: TropicalTidbits

Different models all valid next Sunday evening
Source: TropicalTidbits

 

 

 

Next weekend, soon-to-be Ernesto, likely a hurricane at this point, will very likely be offshore the U.S. East Coast. It is way too early to know exactly where it goes from there, but the cut-off low likely to be near the U.S. East Coast by that time could sling Ernesto northward into Atlantic Canada, or it could miss the connection and get squashed or pushed eastward out to sea. It appears to be too far east to affect our region, perhaps except the immediate coast, unless it gets into the perfect position relative to the upper-level low to get slingshot northwestward inland into New England. For now, we will assume that Ernesto will not have a direct impact to our region, and somewhat cooler and drier weather is expected early the following week (though with uncertain timing as previously mentioned) behind the likely weekend cut-off low. Long-range ensembles suggest that it could turn hotter than average with broad ridging encompassing most of the contiguous U.S. and southern Canada, similar to the end of July and beginning of August. However, confidence is not particularly high with no strong teleconnection signals, albeit with a slightly negative PNA and positive AO which would argue for broad upper-level ridging in our region and a lack of high-latitude ridging to push unseasonably cool air masses into our region. Still, with the lower sun angle and average temperatures dropping now, extreme heat is unlikely, especially given all the rain we have had recently. It is more likely to be an extended stretch of mildly to moderately hot and humid weather.

Source: TropicalTidbits

Source: Climate Prediction Center