Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Pittsburgh PA
1219 am EDT Sat Nov 1 2014
low pressure will cross the region through Saturday with
unsettled weather. High pressure returns early next week.
Near term /through today/...
a rapidly filling area of low pressure at 850 mb is evident smack
dab over the forecast area as of midnight. Weak flow around this
is bringing moisture in from the east...and managing to force just
a bit of precipitation out of said flow via weak low level
deformation. The net result is widespread very light rain and
drizzle across the region. The only exception to this is generally
about 2900 feet in the ridges...which is mainly Tucker
County...where a bit of light snow has been mixed in at times.
Given the rather steep lapse rates...this is not particularly
As the 850 low fills and the surface low recongeals over the
Carolinas by morning...flow will turn progressively more northerly
from late tonight into the morning hours. This will finally start
to drag some colder air into the area. 850 mb temperatures will
start to fall off during the day from around -2c at sunrise toward
-6 to -8c by afternoon. Even with the departure of the best large
scale forcing to the southeast and the deepest moisture with
it...light rain will likely change to light snow in the ridges
before the moisture departs. Otherwise...precipitation chances
slowly diminish elsewhere. The lone exception to this will be as
flow becomes more northerly...lake effect bands off of Lake Erie
may come into play. At the moment...one massively dominant band is
evident in northeasterly flow coming off the lake to the west of
Cleveland. As the flow backs by Saturday afternoon...this dominant
band is likely to break up into multiple smaller bands that could
well affect all of our northern tier of counties. While inversion
heights are falling by that juncture...steep low level lapse rates
may suffice to maintain some bands toward our forecast area. While
the surface is unlikely to be cold enough to sustain any
accumulation outside the ridges...a few snow flakes may start to
mix in by late afternoon from Coshocton to Franklin in this
activity. However...even in the ridges...given marginal
temperatures and weak precipitation rates...any accumulations
should be minor and confined to grassy areas. Fries
Short term /tonight through Monday night/...
widespread freezing temperatures expected Sat night...significant despite having passed date
of average freeze with several counties not yet having experienced a hard freeze.
Cloud cover will help slow cooling process...but cold advection will
The deep trough pulls east Sunday morning...with skies clearing
as a midlevel ridge begins to approach. Sunday night will be
mostly clear and cold as the surface high drifts by to our south.
After a cold start temperatures will begin to moderate Monday as
surface ridge shifts east and southwest flow returns. Only a few
high clouds increasing late day Monday. Middle and high clouds will
be on the increase Monday night and will help hold temperatures in
the middle and upper 30s.
Long term /Tuesday through Friday/...
a cold front crossing the region later Tuesday into Wednesday
with a chance for showers. Next front and push of colder air timed
for Thursday with showers which look to end as snow showers in the
ridges Friday morning. Close to wpc forecasts through the period.
Aviation /04z Saturday through Wednesday/...
widespread MVFR conds and showers are expd into Sat morning as a deepening
upper trough advns across the Great Lakes and Ohio Valley region. With low level moisture
in place some patchy IFR is also possible tonight. Deep moisture is
prognosticated to dcr Erly Sat as coastal surface low pressure develops in response
to the digging upper trough...decreasing the shower covg over our region. MVFR SC
and scattered showers are expd to continue however through Sat with cold air
Outlook.../Saturday night through Wednesday/...
ceilings rstrns are experimental into Sun morning in cold northwest flow. Rstrns are possible
again with a middle weak cold front.