Area Forecast Discussion
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FXUS61 KPBZ 182337

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

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


A good bit of clearing is already occurring as diurnal
stability quickly takes hold along with dry air advection in the
column. This is even as the upper trough and a decent cold pool
transits generally to the north of the area. Model time height
sections do suggest some potential for fog where the winds drop
off, however given ample drying this afternoon with sunshine and
breezy conditions, it seems the chances of anything widespread
are fairly low.

With drier air rolling in, lows will be down from recent nights,
and lower dewpoints will lead to better sleeping weather. Even
still, lows should trend just slightly above normal. Fries


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.

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.


- 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

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.


Conditions will rapidly clear over the next hour or two and
nearly calm conditions may produce some valley fog, but this
should largely be limited to favorable sheltered locations.
Depending upon how well mixed the lowest portion of the
atmosphere stays, a bit of boundary layer topped stratus will
also be possible in upslope areas by morning.

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.

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




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