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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS61 KPBZ 040515
AFDPBZ

Area Forecast Discussion
National Weather Service Pittsburgh PA
115 AM EDT Wed Oct 4 2023

.SYNOPSIS...
Dry and seasonably warm weather is expected through most of
Thursday under the influence of high pressure. A strong upper
level low will bring cooler air and periods of rain to the
region late Thursday night through the weekend.

&&

.NEAR TERM /THROUGH TONIGHT/...
-- Changed Discussion --
Expect another morning of river valley fog developing after a
night of clear skies under high pressure. Strong radiational
cooling be The result will be morning low temperature ending
around 5 degrees above the daily average.

The setup heading into the coming day will feature the
initiation of a pattern change as an upper level trough begins
deepening across the central plains and edges the ridge to the
east coast. The Upper Ohio River Valley will remain under the
influence of high pressure that shifted east, with weak
southerly flow helping to maintain 10-15 degree above normal
daytime high temperatures.

The slow intrusion of high clouds amid moist advection ahead of
the trough should mitigate nocturnal fog development tonight into
Thursday morning, though a few valleys near the Laurel
Highlands may still see patchy development.
-- End Changed Discussion --

&&

.SHORT TERM /THURSDAY THROUGH FRIDAY/...
-- Changed Discussion --
High clouds will continue to spread eastward through the day
Thursday, though southerly flow will maintain well above average
daytime temperatures. Lack of surface forcing and displacement
of jet dynamics west should preclude precipitation across the
region much of the day. However, there remains low probability
for late afternoon convective initiation across far eastern
zones as the upper jet impinges the region.

Precipitation chances are expected to more dramatically increase
and slowly progress eastward Thursday night coincident with
initial shortwave passage ahead of the main trough axis. This
precipitation will be primarily driven by upper-dynamics as the
surface cold front will remain farther displaced west. Due to
this, overnight temperature should remain elevated save for
rain-cooled locales in eastern Ohio.

The surface cold front is favored to cross Friday and aided by
shortwave movement. The combo should foster showers and low
probability thunderstorms ahead of the boundary as it traverses
east through the day. An upper level dry slot should quickly
follow this feature and may promote a brief dry spell that
currently is not captured in PoP values. Deep mixing given
abundant cloud cover is unlikely to occur ahead of the boundary,
which should limit severe threat and keep stronger winds aloft.
Post-frontal passage, steepening lapse rates and deeper mixing
offer potential for gusty wind around 30 mph (probability of 40
mph remains generally below 20 percent and limited to elevation
peaks).
-- End Changed Discussion --

&&

.LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/...
-- Changed Discussion --
The Upper OH Valley region heading into the weekend is expected
to see the deepening of the incoming upper trough over the
Great Lakes region, with periodic shortwaves rounding its base.
This pattern favors a prolonged period of scattered rain shower
chances, seasonably cool temperature, and periods of gusty
winds.

Periodic showers and breezy afternoon winds are likely to
continue Saturday into early next week as the upper low remains
overhead. Areal coverage of precipitation varies and will be
dependent on north-south position of trough as well as wind
angles (which could activate lake-enhanced showers). As 850mb
temps drop below 0 degrees celsius and 700mb below 10 degrees
celsius Saturday night into Sunday, there is a low probability
(less than 20 percent chance) for a precipitation type change
over in the highest terrain, assuming precipitation is even
present during that period. If even snow does occur, temperature
is still marginal enough to likely preclude any accumulation.

Upper level pattern evolution for early next week shows greater
variation, so range of potential outcomes is highest then; mean
values do suggest continued northwest flow over the region after
the trough axis that will create mainly lake enhanced showers
over northwest PA and continue seasonably cool temperature.
-- End Changed Discussion --

&&

.AVIATION /05Z WEDNESDAY THROUGH SUNDAY/...
-- Changed Discussion --
With little change in the air mass have largely gone with a fog
forecast based off the previous 24hrs at individual TAF sites,
with restrictions confined to valley ports. Vis restrictions
will lift quickly with daytime mixing. Outside of valley fog,
high pressure centered northeast of the region will maintain VFR
and light SSE wind.

.OUTLOOK...
Outside of early morning river valley fog, VFR is expected
through Thursday under a large area of high pressure.
Restrictions are likely with rain late Thursday night through
most of the weekend with the approach and passage of a cold
front, and with a subsequent crossing upper low and cold
advection.
-- End Changed Discussion --

&&

.PBZ WATCHES/WARNINGS/ADVISORIES...
PA...None.
OH...None.
WV...None.

&&

$$

SYNOPSIS...Shallenberger
NEAR TERM...Shallenberger
SHORT TERM...Frazier/Shallenberger
LONG TERM...Frazier/Shallenberger
AVIATION...88