Plain-language summary:
Cloudy and showery weather dominates
again through Tuesday, especially south of the U.S./Canada border, with warmer and
sunnier conditions expected to the northwest, except
for isolated thunderstorms. It turns hot on Wednesday and
Thursday, especially west of the Appalachians, with showers and thunderstorms
likely on Friday from Vermont on northwestward but still hot to the east. It
will likely turn cloudier, rainier, and somewhat cooler again next weekend or early the following week, though
the clouds and high humidity means that nighttime lows will still be relatively
warm. No heat waves are expected for a while afterwards as well, as cloudier
and stormier than usual conditions for July continue.
Meteorological discussion:
After a hotter day southeast of the
St. Lawrence Valley yesterday, it is turning cloudy and cooler yet again today,
especially south of the U.S./Canada border. A weak disturbance, debris convective clouds and
low-level moisture from yesterday and yesterday night’s rain will keep most of
Northern New England cloudy today, with rain from southern Vermont to
southern Maine. The northern Champlain Valley on north and west will stay
mainly rain-free, except
for isolated thunderstorms, unlike yesterday, with increasing amounts of sunshine heading
northwest. It could reach 28-30C (82-86F) over the sunnier locations in eastern
Ontario.
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| Source: Penn State Meteorology |
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| Source: TropicalTidbits |
Meanwhile, another slow-moving but
relatively weak low pressure system is approaching from the west, and will be
over central New England by Monday and Tuesday. This will cause cloudy and showery
conditions underneath, with it turning drier, sunnier, and hotter heading
northwest, especially northwest of the St. Lawrence Valley. It will likely be warmer, especially on Tuesday with more sunshine but also more instability that could lead to more showers and thunderstorms. Localized
heavy rain and flooding could occur again from southern Vermont to southern Maine, with localized amounts through Tuesday night of 4” (100 mm) possible, with much less of a threat heading to the northwest.
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| Source: TropicalTidbits |
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| Source: PivotalWeather |
It will heat up noticeably Wednesday
and especially Thursday as ridging briefly takes over. On Thursday, widespread
88-93F (31-34C) temperatures are expected at low elevations of the Champlain
and St. Lawrence Valleys that get downsloped with the weak southerly flow, with
the ridging likely preventing any convective storms or limiting them to
isolated areas over higher terrain. East of the Appalachians will be slightly
cooler, with no downslope flow, especially near the coast, where the sea breeze
will also cool it off.
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| Source: TropicalTidbits |
The hot spell will be cut shorter than
earlier expected as yet another trough approaches from the west and slows down.
Friday will likely still be hot from the Champlain Valley on southeastward, but
this depends on the exact timing of the cold front that will bring showers and
thunderstorms with it. As the trough possibly stalls over the weekend and into the following Monday, more
cloudiness and storminess is likely, with somewhat cooler temperatures but
still high humidity as most of the cooler, drier air mass gets modified and deflected
to the northwest. It is uncertain just how long the storminess will last, but
it could be a few days before it turns drier again, at which point the air mass
will likely be somewhat cooler and not supportive of a hot spell.
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| Source: TropicalTidbits |
The -NAO and associated high-latitude blocking
that subsided somewhat over the past 1-2 weeks is returning and likely not
going away that soon. There is no real +PNA or ridge in western North America
to force deep troughs with truly cool air masses over our area. Rather, the -NAO
appears to promote low pressure systems to tunnel underneath farther south than
usual over our area beneath ridging over northern Ontario and central/northern
Quebec, where it could actually be hotter than over our area. These low pressure
systems will cause cooler daytime highs due to cloudiness and storminess, while
the clouds and high humidity keep nighttime temperatures relatively elevated. Although
some hot days are possible, true heat waves are unlikely, and although it is still
early, it is very possible that the record heat on June 1 could be the hottest
of the entire summer.
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| Source: Climate Prediction Center |
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| Source: TropicalTidbits |
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