Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Pittsburgh PA
533 PM EDT Wednesday Sep 17 2014
dry conditions will continue until the approach of a Sunday cold front.
Near term /through Thursday/...
diurnal cumulus is again dying a swift death across the region as
the earlier sunset limits the hours of the day instability that
supports its development can manage to maintain itself. That
said...there is a very weak short wave trough set to cross the
area overnight. In association with this...a complete dearth of
layer moisture is evident with its passage...so even an increase
of much in the way of cloudiness seems like a stretch.
Behind said short wave trough...Canadian high pressure looks to
reestablish itself over the region on Thursday. This will limit
vertical mixing such that even with abundant sunshine...high
temperatures are likely to be rangebound due to a cool start and
poor mixing. The end result will be a day much like today with
temperatures roughly half a dozen degrees below normal. Fries
Short term /Thursday night through Saturday/...
the reinforced surface high will build off the East Coast by Friday with southerly
flow reinitiating warm...relatively moist advection over the upper Ohio
region. This will cumulate in temperatures surging about 5 degrees above
the avgs by Saturday afternoon...although dry conditions will continue until
the apprch of the Sunday cold front. Short term temperatures were adjusted
using bias corrected GFS MOS.
Long term /Saturday night through Wednesday/...
the apprch of a shortwave/associated cold front on Sunday is expected to
generate the next chance for showers over the region while passage should
surge cooler air back over the region aftr the Saturday warm up.
Models agree that East Coast upper trofg will linger into midweek with northwest
flow off the Great Lakes...but still diverge in magnitude of the
feature...although the latest GFS run projections have eliminated
the closed middle level low previously projected. The long term forecast
is thus of persistence with dry and cool conditions continuing.
Aviation /22z Wednesday through Monday/...
VFR conditions and light surface wind were maintained through tonight...although
stratocu and cumulus will plague the region at least until passage of a
weak front/upper disturbance on Thursday morning. At moment...it apprears that
cloud cover may be sufficient to preclude significant fog restrictions
for all but the northern terminals.
Outlook...Thursday through Sunday...
the next chance for genl restrictions will come with a Sunday cold front.