Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Pittsburgh PA
1210 am EDT Wednesday Apr 22 2015
upper level low pressure over the Great Lakes will maintain cool
and unsettled weather through the week.
Near term /through today/...
no major alterations were necessary for the Post midnight update.
showers will persist and are expected to become more widespread as
a shortwave rotates through the base of the persistent Great Lakes
upper low. The associated surface reinforcing front will provide
focus for the better precipitation chances over the southeastern half of
the County Warning Area later this morning as mixing improves and
meager boundary layer moisture recovers somewhat. Likely to
categorical probabilities were thus maintained with higher numbers
over the aforementioned areas...basically east of a DuBois to
That deepening mixing layer will also support another windy day...albeit
not to the magnitude of Tuesday. Nevertheless...gust around 30 miles per hour
should be expected...35 to 40 miles per hour on the ridges. The precipitation and
cold advection will limit temperatures and highs were forecast about 15
degrees below the averages via persistance and the latest NAM and
Short term /tonight through Friday night/...
although the shortwave is prognosticated to complete passage across the
area by this afternoon...shower chances will persist given the
deep mixing layer resulting from a deep middle level thermal trough
with the low. Better probabilities were forecast over the I 80
corridor and ridges given lake moisture and upslope
ehnancements...and chances...including snow shower in the pre dawn
of Thursday...for those areas were maintained despite dry
advection until that cold pool slides eastward later on Thursday.
Otherwise...cold temperatures can be expected into the weekend
with morning lows near...or a few degrees under the freezing mark.
Long term /Saturday through Tuesday/...
GFS/European model (ecmwf) models have flip flopped over the last 24 hours on
whether the Saturday system will pass across the forecast area or
remain to the south. European model (ecmwf) now has the more northern track while
the GFS has the southern track. Similar to yesterday...ensembles
support the European model (ecmwf) solution...so have added some probability of precipitation back into the
forecast from Pittsburgh south. Temperatures will remain below
normal through the extended forecast...with several nights of near
Aviation /04z Wednesday through Sunday/...
a shortwave and reinforcing cold front will bring a 4 to 5 hour
period of MVFR in showers before daybreak west and southern
ports...with patchy MVFR north. As system quickly exits midday
strengthening pressure gradient in cold advection will allow for
west winds to gust toward 30 kts.
Outlook.../Wednesday through Sunday/...
periodic restrictions are possible much of the period mainly
north of kpit as the upper trough persists over the Great Lakes.