Area Forecast Discussion
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FXUS61 KPBZ 170939

Area Forecast Discussion
National Weather Service Pittsburgh PA
539 AM EDT Thu Aug 17 2017

Rain is likely with a cold front later today and into Friday.
Temperatures will stay warm through the weekend.


The quasi-stationary boundary over Southern Ohio will be pushed
northward as a warm front this morning, by a rather vigorous
shortwave that will move across Northern Ohio, reaching
Northwestern Pennsylvania by early this afternoon. This will
eventually place the entire area well into the warm sector, and
pump up humidity levels. With the late morning wave, models are
keeping most of the activity to the north, closer to its path,
while south of this, convection looks to be more scattered or
isolated. There will be some limiting factors to storm
development and intensity that will need to be closely watched
today. The main one, at least through the afternoon, will be the
very warm air aloft, which will provide a cap on the
atmosphere. In addition, cloud cover associated with the morning
wave, will work to limit sunshine, and readings may fall short
of forecasted convective temperatures. If the cap is strong
enough, cloud cover could decrease as the afternoon progresses.
This will all need to be closely watched today.

By late this afternoon and into the early evening, the
aforementioned shortwave will be moving rapidly over North-
Central Pennsylvania. Another, weaker shortwave trough, will
move into my Ohio counties by early evening. Models are
redeveloping convection ahead of this second wave, moving it
eastward during the remainder of the evening hours. At this
time, it appears the NAM is struggling with convective feedback,
due to an over amplification of the omega field and by trying
to develop a cool pool aloft with the wave, which does not seem
to be realistic. Additionally, the NAM may be overdoing the PWAT
values for today, but I do think, with dewpoints pushing toward
or into the 70s, heavy downpours will be a concern. The good
news is that the pattern will be progressive, with forecasted
storm motion of 20 to 24kts, so individual cells should be
moving quickly.


Shortwave trough will be east of the area shortly after
midnight. Once the large scale ascension moves east, and
diurnal stabilization overtakes the atmosphere, expect the
activity to not only move east, but also weaken. Will keep in
the risk for showers/storms overnight, with the higher PoPs
drifting eastward with the exiting wave.

Lingering showers are possible Friday morning, although the
coverage is questionable, as the best lift will be well to the
northeast and well to the southwest of the region. It`s likely
that models are filling showers in through the entire trough
axis, which would focus the activity over the southeastern
quadrant of the area. As afternoon approaches, the trough axis
will shift southeastward toward the Mid-Atlantic region, which
should bring an end to the risk of showers, save for the far
southeastern ridges.

The cold front will finally begin to cross the area late Friday
afternoon reaching Northern West Virgina by late evening. By
this time, the best lift will be southeast of the area as will
be the deep moisture. Because of this, have decided to leave
FROPA dry, but this will likely need to be further investigated
in future model runs.

Cooler air will overspread the area Friday night and Saturday.
A strong shortwave trough will cross the region late Saturday
afternoon and evening. Have decided to go with slight to low
chance PoPs with this feature, as there will likely be another
surface boundary accompanying the upper level wave.


Broad high pressure will build across the region for the end of
the weekend into the beginning of the work week. A cold front
should then bring a chance of rain back to the region for
Tuesday and Wednesday. Temperatures will remain near average,
building into the middle of next week.


Valley fog, while indicated in satellite, has had little impact
to the terminals this morning as high clouds increase in advance
of approaching warm front. There may still be brief restrictions
at FKL and KDUJ but otherwise VFR should prevail until very late
in the TAF period.

Warm front associated with northeastward tracking low pressure
will result in some scattered showers and thunderstorms today.
Latest hi res guidance has a few showers in the vicinity of ZZV
by 10am but most of the activity appears to be much later. Kept
the mention of VCTS late this afternoon at all terminals with
deteriorating conditions anticipated with the approach of a
more potent shortwave late.

Wind will be out of the sw under 10kts.

Restrictions are likely through Fri morning as the cold front




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