Plain-language summary:
A stalled front will bring a significant temperature contrast and a lot of rain to the region today through Monday. The front will transition to a backdoor cold front by Monday night and weaken, with most of the rain exiting by Tuesday except a few lingering showers. A brief warmup will follow on Wednesday. Another cold front will quickly push through the region from northwest to southeast Wednesday night and bring an unseasonably chilly air mass for late in the week.
Meteorological discussion:
Today, a strong but almost stalled front is oriented from west-northwest to east-southeast from eastern Ontario to Maine. Summerlike temperatures with some sunshine are dominating to the south, from the southern Adirondacks to southern Maine, while occasional to steady showers, abundant clouds, and much cooler temperatures are dominating to the north.
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| Source: Aviation Weather Center |
The front will slowly push south as two elongated areas of low pressure ride along it. The first one will bring heavy rain to southern Quebec and central Maine this evening. After a short but still cloudy break tonight, the second one will bring heavy rain on Monday to similar or slightly farther south areas, from eastern Ontario and southern Quebec to all of northern New England except northern Maine. A widespread 1.5-2.5" (40-65 mm) of rain is expected in the zone receiving both storms. Localized flooding could be an issue, with scattered heavy downpours embedded in the longer period of lighter rainfall, especially in areas that received very heavy rain (>3 in or 75 mm in spots) on Tuesday, such as parts of the Champlain Valley and the eastern half of the Montreal area. The heaviest rain will pass north of the most severe drought area, as is typical for the last couple of months, but some rains will make it into the drought-stricken parts of the region.
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| Source: TropicalTidbits |
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| Source: PivotalWeather and U.S. Drought Monitor |
After the second low-pressure area moves out by Tuesday morning, the temperature gradient weakens and rain will be limited to scattered showers. However, there will be a lot of moisture in the low-levels left behind with no push of strong winds or dry air to scour it out. With the lower sun angle this time of year, low clouds will be widespread on Tuesday. With the clouds, temperatures will be on the cool side despite the coolest air mass aloft having exited to the northeast.
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| Source: TropicalTidbits and PivotalWeather |
Stronger southwesterly flow will finally scour out the low-level clouds and moisture on Wednesday, with a small piece of the building heat wave briefly making into the region with widespread highs in the 70s F (low to mid 20s C). However, the ridge will remain chiefly in the Midwest U.S. and southern Plains, a distinct change from a few days ago when it looked like the northeast U.S. would share in the heat wave as well.
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| Source: TropicalTidbits |
A very amplified trough will settle in the eastern U.S. by Thursday, dragging a strong cold front through Wednesday night. This amplification and the poor model simulation of it until recently could stem from the extratropical transitions of Typhoons Merbok and Nanmadol in the western Pacific. Strong northwesterly winds, a couple of showers, and unseasonably chilly weather are expected Thursday into Saturday. The first snowflakes of the fall will likely occur on the higher peaks. For now though, it looks too windy for frost and freezes to occur for most except at the high peaks, with a strong low pressure in Atlantic Canada that could be further amplified by Hurricane Fiona's extratropical transition there at that time.
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| Source: TropicalTidbits |
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