Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Pittsburgh PA
244 PM EDT Friday Jul 29 2016
a series of weather disturbances will keep showers in the
forecast through the weekend.
Near term /through tonight/...
a weak surface boundary remains splayed out from Indiana through
Northern Ohio and far northwest Pennsylvania at this hour. To the south
of it, widespread upper 60s to lower 70s remain in a weakly
forced, soupy environment. Steering flow is weak, but instability
seems to be increasing readily as the afternoon wears on given the
dissipation of stratus and formation of cumulus. Showers and
thunderstorms have developed, primarily along the interfaces of
weaker stability left behind by differential heating from a bit
earlier on. The activity that has develop is generally being
propagated along by the cold pools that are developed in-situ,
thus movement has been fairly slow. It does seem that as the
afternoon and evening wears on, a preferential trend toward southeast
movement of activity should develop, resulting in increased shower
and thunderstorm activity in our area.
Upstream convection currently over Illinois and northern Indiana
will likely weaken as it starts to move eastward overnight.
However, residual cloud cover will remain, and this should make a
trend in sky cover toward mostly cloudy result overnight. Cloud
cover will work to hold temperatures up a bit overnight as a
Short term /Saturday through Monday/...
a weakly coupled upper jet structure looks to work across the area
on Saturday with the continuation of a moist and unstable boundary
layer in place. Increasing upper divergence through the day will
allow for the flourishing of showers and thunderstorms over the
area on Saturday. Mid-level moisture flow from east-west will continue
to lift north of the area as the system digs over the region
Saturday night, resulting in the best chances of showers and
thunderstorms slowly translating nneward.
Another wave will dig into the base of the upper level trough by
Sunday afternoon. This will bring another increase in the chances
of shower and thunderstorm activity across much of the area as
the mid-levels start to nominally cool. It will also start to
usher in drier mid and upper level air as it does so. This will
allow for the reduction in the chances of precipitation by Monday
as cooler nwerly flow becomes entrenched over the area. Fries
Long term /Monday night through Friday/...
surface high pressure will build into the area from the western
Great Lakes Monday night into Tuesday. This will allow the area to
remain in cooler northerly flow even as subsidence builds. A dry
forecast will thus be maintained through mid-week.
Ridging at all levels of the atmosphere should thereafter increase
from mid-week Onward as amplification of the pattern is evident on
basically all guidance over the upper Mississippi Valley and
northern Great Lakes during the second half of the week. This
ridge and resultant low level thermal ridge should start to flop
over toward our area by Friday, which at this point looks to be
the warmest day of the next week or so, when temperatures should
push again well above normal. Fries
Aviation /18z Friday through Wednesday/...
VFR conditions this afternoon with minimal thundershower chances.
Exception being kfkl and kduj where some MVFR conditions and ts
possible. Given low level moisture tonight expect a return to
some fog and stratus...but not as dense and as long lasting as
this morning. Precipitation chances will increase for Saturday
ahead of an approaching shortwave.
Outlook /Friday night through Tuesday/...
broad upper troughing should maintain periodic shower and
thunderstorm restriction potential through Monday.