Area Forecast Discussion
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304
FXUS61 KPBZ 271341
AFDPBZ

Area Forecast Discussion
National Weather Service Pittsburgh PA
941 AM EDT Tue Sep 27 2016

.SYNOPSIS...
An encroaching upper low will return rain chances for the latter
half of the week.

&&

.NEAR TERM /THROUGH TONIGHT/...
The only changes made for the late morning update were some upward
tweaks to wind speed as per the increasing pressure gradient between
the Northern Great Lakes low and Mid Atlantic States high. The
resulting south, to southwest wind has already neutralized cold
advection in the wake of yesterdays front, and resuming warm
advection should support highs near the seasonal averages despite
the encroaching, cold upper low.

Partial decoupling and a dry airmass should result in decent
radiation tonight, so no major alterations were needed to already
seasonably cool lows.

&&

.SHORT TERM /WEDNESDAY THROUGH FRIDAY/...
The Great Lakes upper low is forecast to dig southward across the
Upper Ohio Valley Wednesday, settling near KY/WV and cutting off
from the upper level pattern through at least Friday. As models
are coming into more consistent depictions, confidence in the
forecast of showery weather with sub-average temperature is
improving. The better chance for sustained rainfall is over
Northwestern PA where a southeasterly wind will briefly support
transport of deeper Atlantic moisture inland on Thursday. Overdone
omega fields and lack of mid level convergence/frontogenetic
forcing in the current models do not lend confidence to a heavy
rain forecast, nor do ensemble means for the period.

&&

.LONG TERM /FRIDAY NIGHT THROUGH MONDAY/...
Most of the models lift the stubborn upper low from the middle Ohio
Valley at the start of the period into the eastern Great Lakes by
12Z Sunday.  Details of individual waves rotating around the low
remain tricky at this distance, so kept PoPs fairly general, with a
slow decreasing trend through the weekend.  Expect Sunday night into
the first portion of next week to be dry as a flattening ridge
arrives.  Near-climatological temperatures will edge back above
normal by the end of the period with the departure of the upper low.
SuperBlend values were slightly knocked back early in the period,
but later numbers looked reasonable.

&&

.AVIATION /13Z TUESDAY THROUGH SATURDAY/...
General VFR is expected for the period with afternoon wind gusts
of 15 to 20 kts in the tightening pressure gradient over the
region.

.OUTLOOK /WEDNESDAY THROUGH SATURDAY/...
Upper-level low pressure will settle over the region for the rest
of the week. Periodic restrictions in showers, with more sustain
potential at DUG and FKL should be anticipated.

&&

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

&&

$$
15



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