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Area forecast discussion 
National Weather Service Pittsburgh PA
420 am EDT Friday Jul 25 2014

Synopsis...
dry and cooler weather will close the work week...with shower and
thunderstorm chances returning for the weekend.

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Near term /until 6 PM this evening/...
surface high will keep the area dry and comfortable.

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Short term /6 PM this evening through Sunday/...
weekend weather will be dependent on timing and placement of a
series of upper level waves and the movement and location of a
complex surface boundary.

Flow aloft eventually becomes more zonal Saturday. The first upper
level wave will quickly swing through sometime on Saturday. Model
differences with the details begin Saturday and carry through for
the rest of the weekend. At this time...clarifying the details is
an arduous task. For current forecast will lean toward Sunday as
being the best time to see widespread shower and storm activity.
Beginning late Saturday night and continuing through Sunday...
expect to see multiple mesoscale convective system development which eventually could pass
through the region. Again...still need to work out many of the
details.

May also see storms develop Saturday. However...current model data
is showing limited instability at the surface and aloft.
Additionally...forecast soundings for Saturday show a capped
atmosphere through much of the day. 6km shear is above 40kts...but
with the absence of strong buoyancy and high convective temperatures not
positive convection can get started. Would lean toward elevated
convection but even MUCAPE values are not impressive.

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Long term /Sunday night through Thursday/...
the beginning of the long term period will feature the continued
risk for showers and storms as a surface low and cold front with
plenty of upper level support swings through.

System finally exits Monday night...ushering in another period of
dry weather with below normal temperatures.

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Aviation /08z Friday through Tuesday/...
clear skies and calm winds under high pressure will lead to the
formation of mainly valley fog toward daybreak. The terminals the
are typically impacted by valley fog look to have a small window
of IFR but with dew points continuing to drop have not pushed any
visibility below 2sm.

Any fog that develops tonight will burn off after sunrise with
mostly clear skies and VFR conditions.

Outlook.../Friday night through Tuesday/...
restrictions are likely by Sunday as low pressure spreads showers and
thunderstorms over the upper Ohio region. The potential will continue into Monday
with passage of that systems cold front.

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Pbz watches/warnings/advisories...
Maryland...none.
Ohio...none.
PA...none.
WV...none.

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