Well below normal temperatures are a certainty through next weekend
and beyond as a deep longwave trough remains anchored over eastern
North America. In fact, it will turn even colder Friday through the
weekend, with some areas across the higher terrain possibly not
getting out of the 30s for high temperatures on Friday and Saturday.
A highly amplified +PNA pattern will continue for at least the next
10 days, with a strong western ridge and eastern trough. This will
continue to direct fresh batches of modified arctic air southward
into the Great Lakes and New England.
Looking at the details, a potent mid level shortwave will cross the
eastern Great Lakes Thursday night, along with an attendant cold
front. This will bring an increasing chance of showers, which may
mix with some wet snow overnight as cold advection increases.
Friday and Saturday the trough reloads across the Great Lakes, with
a highly anomalous 525DM or lower 500MB vortex dropping into the
Great Lakes and New England, while a secondary push of even colder
air in the low levels pours across the region on Friday. While the
large scale pattern is well agreed upon in model guidance, there has
been a good deal variability in the synoptic scale features with
most model guidance suggesting several embedded shortwaves and
associated surface lows crossing the Great Lakes Friday and
Saturday. Given the timing and placement differences from run to
run, it remains difficult to pin down the most likely time frame of
precipitation.
That said, the strong upper level trough and deep instability
beneath the cold pool will support scattered to numerous rain and
wet snow showers Friday and both days this weekend, with some lake
response possible downwind of the lakes during the overnight and
early mornings as 850MB temperatures become sufficiently cold
enough. Cold temperatures will continue Saturday, with highs only in
the low to mid 40s at best, if there are breaks of sun. Overcast
skies would only yield highs in the upper 30s given 850mb temps
approaching -10C, with some areas across the higher terrain possibly
not getting out of the upper 30s either way.
The airmass will begin to modify a little by Monday, but
temperatures will still run well below normal. Another low is
forecast to move through the Ohio Valley and eastern Great Lakes,
bringing a chance of some additional rain and wet snow showers.