Plain-language summary:
After a relatively rain-free, hot, and
humid day today, more showers and thunderstorms are likely tomorrow, leading to
more flash flooding concerns especially in Vermont and Quebec. Another hot and
humid day on Monday will likely be followed by some more showers and thunderstorms
on Tuesday, and then another round of wet weather is likely on Friday. The persistently
wet pattern could break by next weekend and beyond, with an initial subtle
decrease in humidity followed by a return in modest heat and humidity but with more
scattered showers and thunderstorms.
Meteorological discussion:
Today, there will be a relative lull
in the unsettled pattern. A weak low pressure well to the northwest rotating
around a very persistent and potent vertically stacked low pressure over northern Ontario will
provide weak southerly flow, bringing in modest heat and humidity, with many low
elevation locations reaching 86F (30C), but will be far enough away for minimal
chances of showers and thunderstorms. Another disturbance will move in
tomorrow, sparking more showers and thunderstorms, first over eastern Ontario
and northwestern New York by sunrise, and then spreading to Quebec, Vermont, and New Hampshire later in the morning, and then Maine in the afternoon. The increased clouds and showers will
lead to cooler daytime temperatures, but it will remain very humid. With all
the moisture, localized downpours will occur, leading to more flash flooding, especially
in Quebec and Vermont, given the extremely wet ground from the heavy rains
earlier in the month. Given that the storms will be mostly moving along though and mostly over by late tomorrow night, rainfall amounts will be much lower than with this past week's storm, with isolated amounts of 2"+ (50 mm+).
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| Source: TropicalTidbits |
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| Source: TropicalTidbits |
The broad low pressure over northern Ontario
will only slowly move eastward into Quebec and weaken slightly next week, with disturbances rotating
around it. After another brief break with heat and humidity on Monday, another
round of showers and thunderstorms is likely on Tuesday, though it is too early
for any details. It appears a tad cooler for Wednesday and perhaps Thursday as
the upper-level low and coolest air pass directly to the north, and then there
could be another storm bringing more showers and thunderstorms on Friday. Tuesday's heavy rain appears to be less widespread and intense than Sunday's with a rather weak system, but Friday's could be rather widespread and intense with what for now looks like a stronger system bringing a lot of moisture from the south again. The unusually warm western Atlantic waters will aid in providing extra moisture for the storms.
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| Source: TropicalTidbits |
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| Source: Northeast River Forecast Center and TropicalTidbits |
As the blocking -NAO pattern eases and the broad
low pressure finally weakens and moves to the northeast, we will probably see
fewer disturbances to trigger showers and thunderstorms, with weaker flow aloft
and initially cooler and slightly drier air advected by weak northerly flow on
the back side of the departing broad low pressure. A bit of ridging will likely
take over most of the eastern U.S., with modest heat and humidity gradually returning
but without the potent low pressure over northern Ontario to bring repeated disturbances
to spark showers and thunderstorms. However, the PNA appears to be mostly slightly positive, and the associated western U.S. ridge will probably prevent a big ridge from developing in the eastern U.S. and producing a big heat wave. There also still remains the risk of a slow-moving
cut-off low tracking through the Ohio Valley and mid-Atlantic U.S., tunneling underneath
the main jet stream over Ontario and Quebec, as has happened several
times since May, but the main jet stream could set up far enough south to prevent any systems from truly cutting off.
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| Source: Climate Prediction Center |
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| Source: TropicalTidbits |
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