Area Forecast Discussion
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FXUS61 KPBZ 261134
Area Forecast Discussion
National Weather Service Pittsburgh PA
734 AM EDT Mon Sep 26 2016
Showers and scattered thunderstorms can be expected with the
passage of cold front today.
.NEAR TERM /THROUGH TONIGHT/...
The only changes needed for the post dawn update were tweaks to
cloud cover and wind based on the latest obs and model soundings.
A deepening trough over the Great Lakes will pull a cold front
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 average low temperatures in the wake of the
.SHORT TERM /TUESDAY THROUGH TUESDAY NIGHT/...
Temperature advection will be quickly neutralized on Tuesday, with
warm advection resuming on the southeastern flank of Great Lakes
low pressure. As such, temperatures were forecast near the seasonal
.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
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 /11Z MONDAY THROUGH FRIDAY/...
VFR will give way to condition deterioration this afternoon as a
cold front sweeps across area terminals. General MVFR is anticipated
with the feature, with IFR visibility in heavier convective activity.
As mixing improves today, expect gusts of 15 to 20 kts, with higher
values in any aforementioned convection.
Improvement can be expected through the evening as subsidence and
dry advection erode clouds and precip. Sufficient wind to prevent
fog is anticipated overnight, with VFR continuing through Tuesday.
.OUTLOOK /TUESDAY NIGHT THROUGH THURSDAY/...
The next chance for restriction is expected Wednesday as upper
level low pressure settles over the area.