Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Pittsburgh PA
758 PM EDT Thursday Jul 24 2014
dry and cooler weather will close the work week...with shower and
thunderstorm chances returning for the weekend.
Near term /until 6 am Friday morning/...
drier air continues to filter into the region on the heels of a
rather brisk northerly flow. Upstream dewpoints really fail to
fall off much more than they already are in northwestern
Pennsylvania...so while surface high pressure is forecast to drop
directly over the forecast area by morning...even with a dearth of
wind during the prime radiational cooling hours...thermal free
fall is not really expected. That said...current resident
dewpoints to our north are generally in the upper 40s...so
areawide middle 40 to lower 50 degree readings will be fairly
common. This is still far below normal for this time of the year.
For reference...the record low for tonight...51f from 1953. Will
be extremely close to that reading by morning at the Airport.
Short term /6 am Friday morning through Sunday/...
high pressure at the surface and northwest flow aloft will provide
a comfortable Friday with plenty of sunshine.
More zonal flow is projected by Saturday in response to low pressure
digging toward the northern plains. Southward dipping jet is likely to increases deep
layer shear over the region and may spprt severe thunderstorm chances should
timing/instability parameters cooperate. For now...the Storm
Prediction Center has touched the upper Ohio region with a slight
risk...and that situation will be further evaluated during the next
cpl of days as current models suggest morning passage of the necessary
Long term /Sunday night through Thursday/...
phasing of the aforementioned low with a James Bay low is prognosticated
to develop a high amplitude trough over the eastern Continental U.S.. following shower
chances undr the immediate Crossing of the middle level trough axis...the
trend is of dry and cooler conditions.
Aviation /00z Friday through Tuesday/...
clear skies and calm winds under high pressure will lead to the
formation of valley fog tonight. The terminals the are typically
impacted by valley fog could drop in visibility to 1/2 or 1/4 sm. At this time...lower
confidence in fog development away from river valleys tonight...so
expecting terminals including pit to have light MVFR fog restrictions.
Any fog that develops tonight will burn off after sunrise tomorrow
with mostly clear skies and VFR conditions.
Outlook.../Friday through Monday/...
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.