Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Pittsburgh PA
314 PM EDT Wednesday Aug 20 2014
occasional showers and thunderstorms can be expected through the
weekend as a series of disturbances move through the region.
Near term /through tonight/...
flooding issues continue across the warned areas despite batch of
heavy rain has finished and moved east. Recent satellite imagery trends
display dry air aloft moving across the Ohio Valley behind the
passing shortwave. Destabilization is continuing this afternoon...especially
where clearing is occurring...with high surface moisture in place.
Slow moving upper level low over the Great Lakes generating a
shortwave may progress east towards the forecast area this
afternoon to help initiate convection. Thus...high chance probability of precipitation
were maintained through the evening to where the surface boundary
is draped across. Convection is then expected to decrease later
this evening with the loss of heating and displacement of the
Temperatures are expected to be slightly above normal for today
Short term /Thursday through Friday night/...showers and
thunderstorms will continue to impact the region through Friday as
several upper level disturbances pass through and a quasi-
stationary boundary remains in place. Main concern continues to be
flooding as precipitable waters will quickly shoot up to over two Standard devs
above normal after the brief decrease today. However...bulk shear
will also be around 30-40kts so several strong to severe storms
are not out of the question. Opted to hold off on any flood
watches for now as there is still uncertainty in the location of
the most favorable dynamics both days.
Long term /Saturday through Wednesday/...
with active weather in the near term...generally stayed close to the
previous forecast blending with wpc thinking for the extended
period. Models continue to show a ridge building in the Southern
Plains through the weekend...slowly shifting the axis into our
region by early next week. The weekend will remain warm and muggy
with daily rain chances as we sit on the eastern periphery of the ridge.
A gradual eastward shift in the upper trough axis would mean a
continuation of at least near normal temperatures through middle of next
week with a drying trend.
Aviation /19z Wednesday through Monday/...
VFR conditions the remainder of day with chances for seeing
thundestorms at any one location low as coverage should be
isolated this afternoon and evening. Thunderstorm coverage will
become greater on Thursday as a disturbance passes across the
region...with MVFR visible restrictions during any on site activity.
Outlook.../Thursday through Sunday/... several crossing
disturbances will cause periodic restrictions into the weekend.