Area Forecast Discussion
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FXUS61 KPBZ 241831
AFDPBZ

Area Forecast Discussion
National Weather Service Pittsburgh PA
131 PM EST Fri Nov 24 2017

.SYNOPSIS...
Dry weather is expected today. Shower chances return with the
approach and passage of a Saturday cold front.

&&

.NEAR TERM /THROUGH TONIGHT/...
Current regional satellite imagery shows a general lack of cloud
cover over the area. Southerly flow and insolation has brought
temperatures back above average today.

Clouds will begin to increase tonight ahead of the weak system
expected tomorrow. High and mid-level clouds will move in
first, well ahead of the low-level moisture closer to the cold
front. Even if the clouds remain fairly opaque through the bulk
of the night, the boundary layer should remain fairly well
mixed. This, combined with rising dewpoints, will all mean that
lows tonight will be considerably warmer than last night`s
values. Lows should come in 5-10 degrees above averages.

&&

.SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/...
A shortwave in broad upper troughing, and it`s associated cold
front, are progged to track from the Midwest to the Great
Lakes/Ohio Valley region by Saturday. Models trending a few
hours slower with bringing in the cold front, so timing has been
adjusted. While the best forcing remains well north of the
area, favorable placement of the upper-level jet should provide
enough support for the low chance PoPs to be maintained. Still
some question as to whether enough moisture can be scraped
together, as there is considerable overrunning of what mid and
upper-level moisture does exist. All told, the cold front should
pass with little precipitation, falling as liquid through
Saturday evening.

Upper-level trough swings through Saturday evening, injecting
slightly deeper moisture and bringing cooler mid-level air. This
should help to re-invigorate shower activity, at least for a few
hours. Highest PoPs will be maintained north of I-80 and in the
higher elevations. Sometime around midnight, cooling aloft
should reach the point where rain can transition to snow. Not
expected much more than a coating for most locations north of
I-80 and in the Ridges, but a few locations could see up to a
half an inch. Low clouds may hang around well into Sunday,
especially north of Pittsburgh, but the inversion heights will
have dropped to the point where shower activity will no longer
be supported.

A weak surface trough should result in some cloud increase
Sunday night mainly north of Pittsburgh, though precip is not
expected. After near to above average temperatures tonight and
Saturday, a return to temperatures below seasonal levels is
expected Sunday.

&&

.LONG TERM /MONDAY THROUGH FRIDAY/...
Generally dry weather is expected through early in the week
with a de-amplified flow aloft. A weak trough is progged for a
Tue night/Wed passage, with mainly just an increase in clouds.
Another trough could result in better precip chances by late
week. Temperatures are expected to average near to several
degrees above seasonal levels.

&&

.AVIATION /19Z FRIDAY THROUGH WEDNESDAY/...
Clear sky this afternoon will give way to high clouds tonight as
high pressure moves off to the east. S/SW wind generally from 10
to 15 knots this afternoon will diminish a bit tonight at the
surface. However, a low level jet ahead of an approaching front
will bring low level wind shear concerns overnight. The jet
weakens as the front approaches after sunrise on Saturday,
ending the LLWS threat, but clouds will continue to thicken and
lower. Scattered showers are possible after 12Z, with ceilings
starting to lower towards MVFR levels by the end of the TAF
period.

.Outlook...
Restriction potential will continue through early Sunday, as cold
northwest flow changes scattered rain showers to snow showers.

&&

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

&&

$$



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