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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS61 KPBZ 260750
AFDPBZ

Area Forecast Discussion
National Weather Service Pittsburgh PA
350 AM EDT Mon Sep 26 2016

.SYNOPSIS...
-- Changed Discussion --
Showers and scattered thunderstorms can be expected with the
passage of cold front today. More seasonable temperatures are
expected for the rest of the week.
-- End Changed Discussion --

&&

.NEAR TERM /THROUGH TONIGHT/...
Deepening trough over the Great Lakes will push a cold front,
currently analyzed over eastern Indiana, across the Upper Ohio
valley this afternoon. Model consensus on timing is relatively
good between the deterministic models and the hi res short term
guidance. As such, very little adjustment was needed to
categorical probabilities with strengthening support for
thunderstorms as the boundary approaches southwestern PA/northern
WV. This will be where surface instability is likely to be the
highest based on the boundary`s timing, and less cloud cover.

The NAM is the most robust with it`s CAPE/dewpoints compared to
other model guidance, including the RAP and HRRR soundings, which
it tends to overdue in most convective scenarios. However, with
deep layer shear present and at least modest cape of 500j/kg,
some strong to severe storms may be possible which is supported
by the spc marginal risk over the aforementioned region.

Strong southerly flow and sunshine in advance of the boundary
should allow for temperatures to warm above seasonal averages this
afternoon followed by normal low temperatures with the fronts
passage progged to be east of the ridges by midnight.

&&

.SHORT TERM /TUESDAY THROUGH TUESDAY NIGHT/...
Temperature advection will be rather weak on Tuesday with
southwesterly flow expected aloft with the upper trough still
situated over the northern Great Lakes and high pressure present
at the surface. Thus, temperatures were forecast just below
seasonal averages.

&&

.LONG TERM /WEDNESDAY THROUGH SUNDAY/...
Most of this period will be dominated by the closed upper
low...which will dive from Michigan into the central Ohio Valley by
Thursday and linger as a cutoff through at least Friday.  Models are
beginning to converge on this scenario, with the lagging GFS finally
coming around.  As such, mostly chance PoPs were maintained through
the remainder of the work week for scattered showers.  Timing of
shortwaves around the upper low remains tricky at this distance.
Given the upper low representing a pattern change, felt the
SuperBlend temperatures were a bit too high and knocked them back a
couple of degrees early on, keeping daytime values a bit below
climatology.

The upper low should begin to lift out by next weekend as midlevel
heights build over the lower Ohio Valley.  This will bring dry
weather back by Sunday, as well as allow temperatures to recover
back to seasonal levels.

&&

.AVIATION /08Z MONDAY THROUGH FRIDAY/...
Mostly VFR conditions are forecast through midday. The lone
exception may be near DUJ around sunrise, as some low clouds try
to creep up the ridges on southeast upslope flow. Handling with a
MVFR TEMPO for now but may need to adjust depending on satellite
trends.

Conditions will deteriorate during the afternoon with the approach
and passage of a cold front. A short period of MVFR or even IFR
visibilities in showers or thunderstorms is expected, but timing
remains a bit problematic still. Used VCTS and expect to refine
timing in future updates. Some of the storms may be strong, with
heavy rain and gusty winds.

Behind the front, MVFR ceilings will linger for a few hours into
the evening hours, until drier air sweeps in from the west,
allowing for clearing skies.

.OUTLOOK /MONDAY NIGHT THROUGH THURSDAY/...
The next chance for restriction is expected by Wednesday as upper
level low pressure settles into the area.

&&

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

&&

$$