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000
FXUS61 KPBZ 181843
AFDPBZ

Area Forecast Discussion
National Weather Service Pittsburgh PA
243 PM EDT Fri Aug 18 2017

.SYNOPSIS...
Showers and possibly strong storms could roll through Saturday
afternoon and evening. Sunday will be the better of the two
weekend days for outdoor activities. Less humid this weekend as
well.

&&

.NEAR TERM /THROUGH SATURDAY/...
Tonight, some clearing will be realized, but we will remain
under the influence of the upper trough. This could work in some
additional clouds, but meager moisture will quell any shower
chances. Lows will remain just above seasonal average values,
but with lower dewpoints invading, it will feel much fresher.

Another, fast-moving, shortwave trough will move into the area
tomorrow. Bolstered by cooling mid-level temperatures,
developing showers and thunderstorms should move quickly through
the forecast area. Model soundings show a speed max in the mid-
levels, coincident with at least some modest instability. This,
and the lowered freezing level to near 10kft should be enough to
pose at least a marginal severe threat in the afternoon hours.
Will continue to monitor this in the coming updates.

&&

.SHORT TERM /SATURDAY NIGHT THROUGH SUNDAY NIGHT/...
A line of showers and storms will be exiting northern West Virginia
and the mountains of southwest Pennsylvania and western Maryland
early Saturday evening.  Dry weather will be invading from the west
with differential anti-cyclonic vorticity advection moving in.
Benign weather takes hold the balance of the short term.

Lowering humidity with dewpoints in the lower 60s will give us a
break from the recent run of upper 60s to lower 70s Sunday.  H8
temps hover around seasonal norms /14C/ correlating to daytime highs
in the upper 70s to lower 80s.  Bias corrected all blend was used
for temperatures.

&&

.LONG TERM /MONDAY THROUGH FRIDAY/...
Highlights:
- Warm and Humid Monday and Tuesday
- Cold Front Crosses Tuesday night into Wednesday
- Dry and Below Normal Temperatures

H5 heights above 590dm yield a warm afternoon Monday, however
mid level temps and proximity of high pressure over the mid
atlantic will keep the day dry. Down the road, isolated storms
could fire due to the elevated heat source in the higher terrain
so Monday afternoon / evening isolated to scattered pops may be
added.

The main weather feature of the long term is a cold front
crossing Tuesday night into Wednesday morning. Long range models
provide above average confidence to warrant likely pops for the
entire region. With the boundary passing Tuesday night, do not
foresee a severe weather threat. High water is also not a
concern at this time with the speed of the system as it
traverses through the forecast area.

In wake of the baroclinic zone sprawling high pressure building
south from the Great Lakes offers cooler weather as H8 temps
fall below 10C. The passing mid level trough axis could ignite
daytime showers mainly north of Lake Erie Wednesday afternoon.
Added a slight chance for the aforementioned area.

Temperatures were constructed using a mixture of the Superblend
and Allblend.

&&

.AVIATION /18Z FRIDAY THROUGH WEDNESDAY/...
Showers and thunderstorms are dwindling west to east this
afternoon, but some re-development could occur along the cold
front still in the area.

Outside of any brief shower/thunderstorm this afternoon, VFR
conditions are expected in altocu. Winds will increase through
the afternoon, gusting occasionally to near 20kts.

Tonight, clear and nearly calm conditions could produce some
valley fog, but this should largely be limited to favorable
sheltered locations.

Saturday, a fast moving disturbance will bring additional brief
restrictions as shower and thunderstorm chances increase in the
afternoon hours. Otherwise, VFR conditions are expected.

.Outlook...
VFR conditions are expected the latter part of the weekend,
marred only by pre-dawn valley fog.

&&

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

&&

$$