Plain-language summary:
Today will be the first day since
Friday of last week to reach near to above average temperatures for most. After
an even warmer Monday except in eastern Ontario and northwestern New York where
clouds will arrive sooner, rain and thunderstorms will move through the region
from southwest to northeast Monday evening through Tuesday afternoon. Somewhat cooler and showery weather will return
for Wednesday through Friday, though not as chilly as this past week. Warming
and drying is expected this weekend, and perhaps the following week as well,
though there could still be some cool, showery pockets that are not as
long-lasting and intense as the one this past week.
Meteorological discussion:
The slow-moving vertically stacked
storm is weakening and finally moving off to the east, taking the unseasonably
cool, cloudy, and showery weather with it. Today will be the first day since
last Friday to reach near to above average temperatures for most, as ridging
briefly builds in, allowing for a warmer air mass and more sunshine. The air
mass will warm further by Monday due to southerly flow ahead of another almost
vertically stacked low slowly moving eastward that will be over the eastern
Great Lakes. Clouds ahead of it will keep eastern Ontario and
northwestern New York cooler, while more sunshine will lead to warmer
temperatures farther east, except along the Maine coast where the onshore southerly
wind will bring in cooler maritime air.
The surface low pressure will move
northward to the Ontario/Quebec Monday night, with a line of showers and possibly
thunderstorms associated with the storm’s cold front affecting most of the
region. It will likely be the strongest over northern New York, eastern Ontario, and southern Quebec, where
although it will not be particularly hot and humid, enough daytime heating for
some modest instability could occur. The southerly flow will also pull some
Gulf of Mexico moisture into our area, a rarity for the past month, leading to
higher humidity and the potential for heavier rainfall, possibly >1” (25 mm)
in many spots. With the rain and more humid air mass, dew points will be the
highest seen so far this year Monday night into Tuesday. The line will likely
weaken late Monday night into Tuesday morning as it moves into New Hampshire, Maine, and eastern Quebec as instability wanes with the loss of daytime heating.
A pocket of cold air aloft associated
with the upper-level low and broad general upper-level troughing behind the
cold front will lead to modest instability and showers, especially in the
afternoon and evening. This will once again lead to cooler temperatures, but
not nearly as cool as this past week, with the upper-level low being weaker and
faster-moving. As such, temperatures will be less than 10F (6C) below average except
for the few areas under more persistent cloud cover and rain. This will be most
pronounced in the core of the upper-level low, which will move from the eastern
Great Lakes on Wednesday to eastern New England on Friday, weakening along the way.
The upper-level low will move out of
the region by next weekend, leading to warming and drying conditions with more
sunshine. The upper-level pattern across North America will generally feature a
trough in the Pacific Northwest and a ridge in the Plains, extending from Texas
to Manitoba and likely into the Great Lakes as well. Normally, this pattern
will lead to abundant sunshine with westerly or west-northwesterly flow aloft bringing
in relatively dry air, as well as surges of heat from time to time. However,
the persistent -NAO and associated high-latitude blocking pattern could lead to
more slow-moving upper-level lows in our area, leading to pockets of cooler,
showery weather. But with the +PNA and ridge in western North America mostly gone, it is
likely that any cool pockets will be relatively short-lived, and it would be
difficult to completely avoid the warmth and likely humidity from reaching our
area at least occasionally.
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