Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Pittsburgh PA
1244 am EDT sun Aug 2 2015
dry weather and seasonal temperatures will finish the
weekend...then a cold front will bring a chance of showers on
Near term /through today/...
weak surface ridge across the upper Ohio Valley will shift east
overnight...with mainly clear skies and seasonal temperatures.
Southwest flow ahead of an approaching cold front Sunday will give
increasing high clouds...with temperatures in the lower to middle
Short term /tonight through Tuesday/...
although the chance for showers will increase Sunday night...cold
front should make its passage across the region sometime Monday
morning. Did not feel comfortable enough to bump up probability of precipitation to likely
over a widespread area with moisture as a possible limiting
factor...although dynamics along the front are favorable. For now
have simply added likely probability of precipitation north of the Interstate 80 corridor.
Storm Prediction Center has a marginal risk for severe weather on Monday. Two critical
factors will be timing of precipitation along the front along with
instability values (nam has about 3 times as much instability as
GFS...likely due to wet bias of surface dewpoints).
Accompanying the surface cold front will be an upper level low
over southern Ontario. With the proximity of the low...shortwaves
will begin to crank around the low. NAM/sref bring a shortwave on
Tuesday across the region from the north...while the GFS/European model (ecmwf)
keep the shortwave to the north. Between the shortwaves and the
cold front eventually stalling out south of the area...have gone
with a blanket low chance of showers in the forecast. Diurnal
spread in temperatures will shrink by a few degrees due to cloud
cover through the period.
Long term /Tuesday night through Saturday/...
upper trough will remain situated over the eastern US through the
long term with several shortwaves prognosticated to help deepen it through
the period. This will likely keep temperatures just slightly cooler
than seasonal averages. By late in the week...model guidance
suggests a surface wave could develop and lift across the Ohio
Valley late. But...with run to run inconsistency opted to stay
closer to wpc guidance values...which keep chance probability of precipitation through the
beginning of next weekend.
Aviation /06z Sunday through Thursday/...
general VFR will continue into Sunday with dry surface high
pressure suppressing precipitation under northwest flow aloft.
Outlook...Sunday night through Thursday...
restriction potential will increase with the approach and passage
of a Monday cold front.