Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Pittsburgh PA
704 am EDT Thursday Jul 10 2014
an upper level disturbance will cross the region today. This will
supply clouds and possibly an isolated shower. High pressure will
build in on Friday.
Near term /until 6 PM this evening/...
no updates needed early this morning as current observational
trends align well with the ongoing forecast. Patchy fog that has
developed overnight mainly along and north of Interstate 80 is
expected to burn off by middle morning. Previous discussion follows..
trough will slowly cross the region this afternoon. Looking at
general moisture levels...it looks rather dry. However...a closer
look at forecast soundings and cross sections shows saturation
occurring between 5000 and 6000ft this afternoon. This would point
toward a cumulus layer developing this afternoon. Next question is will
there be a deep enough layer of moisture to support shower
development. Current soundings don't really point to
this...showing a pretty shallow moisture layer. The exception is
over the ridges where moisture levels are deeper and atmospheric
forcing will be stronger due to a stalled surface boundary. Will
leave most of the area dry...with the exception of the ridges.
With cloud development expected...temperatures will be tricky. Will go a
touch below guidance.
Short term /6 PM this evening through Saturday/...
shortwave will slowly exit the region tonight and heights will
quickly rise in its wake. Surface high will drift down from the
Great Lakes Friday allowing for a dry and comfortable day.
At this time...most of Saturday looks dry as high pressure will
slowly drift eastward. Models are showing activity developing to
our west Saturday afternoon along a frontal boundary. A pretty
strong shortwave trough will ride along the boundary Saturday
afternoon into Saturday night. Early indications are that an mesoscale convective system
will develop over Indiana and Northwest Ohio Saturday afternoon and race
eastward as evening approaches. A couple of factors will be
important on where this complex GOES. First...models are not
showing a huge dip in the upper level height field...keeping the
500mb pattern zonal. This will likely keep the frontal boundary to
our north. Secondly...most of the upper level energy will move
toward Lake Erie which would keep any late day convection across
the far north. Obviously...this entire setup is still days away...
so many changes in model solutions are possible.
Temperatures and humidity levels will creep up on Saturday.
Long term /Saturday night through Wednesday/...
models begin to sag boundary through the upper Ohio Valley
Saturday night. Another shortwave will swing through late Saturday
night...lowering heights and increasing shower/storm chances. It
does appear that activity will weaken as atmosphere will be
stabilizing. This will be the beginning of a more active period
which will last through much of the long term. A series of upper
level disturbances will cross the region ahead of a slow moving
cold front. The front will finally cross the area Tuesday. The
long term will end cooler and drier.
Aviation /11z Thursday through Monday/...
calm winds overnight has allowed for the development of patchy fog
mainly along and north of Interstate 80...which should burn off
between 13-15z this morning. Elsewhere current T/dew point spreads look
are sufficient enough to keep any visible restrictions this morning.
Although a disturbance will cross the region today...cross
sections indicate moisture aloft will be limited to a thin layer
between roughly 5-8kft...so do not anticipate much in the way of
showers or thunderstorms...but we should see some scattered-locally broken
VFR cumulus develop.
Outlook.../Friday through Tuesday/...
restrictions in showers and thunderstorms will be possible