Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Pittsburgh PA
928 PM EDT Monday Sep 15 2014
showers will accompany a cold front tonight. Generally dry and
cool conditions are expected through the week.
Near term /through Tuesday/...
abundant dry air in the column over the region is working to
eviscerate what was once a rather wide expanse of pre-frontal
showers advancing across Ohio. In fact...the lowest tilts from
kpbz show little in the way of activity from this seems to be any
longer reaching the ground. As such...we will be waiting for more
coherent upper support to advance into the area in the next
several hours before much in the way of shower development manages
to sustain itself.
While upper support for lift along the front is rather robust
with a compact vorticity core...strong differential positive vorticity advection...and broad
upper right entrance region associated divergence aloft...pre-
frontal moisture profiles are just not impressive. It still seems
likely that most areas will see showers overnight...particularly
from Pittsburgh northward...but the amounts of rainfall seem
destined to be more nominal than meaningful.
Post-frontal northwesterly flow will gradually turn north on
Tuesday as layer moisture starts to Peel off to the East. Lake
enhanced stratocumulus will fill in behind the front for a time
until the flow weakens considerably by afternoon. This should
allow for diurnal mixing to start to decimate the stratocumulus
shield farther inland and away from Lake Erie. As a
result...cloudy skies should gradually turn partly cloudy by later
in the afternoon. Temperatures will again be below normal as
result of the dreary start...however. Fries
Short term /Tuesday night through Thursday night/...
generally zonal to west-northwesterly 500 mb flow expected middle-week with surface hipres expected to
promote modest drying of low-level air mass. Shortwave trough will cross the
region Wednesday night-Thursday and may invigorate a few showers mainly in northern zones
Thursday morning. Subsidence and renewed drying will Foster a lack of precipitation
chances by late Thursday afternoon as hipres builds at the surface once again.
Temperatures will be relatively consistent during this period. Maxima will be
in the 60s...and minima will be in the 40s.
Long term /Friday through Monday/...
despite broad upper trough in place at the beginning of the extended
period...a surface high will keep probability of precipitation out of the forecast through
the early part of next weekend. High pressure slowly oozes east
through Sat with a front moving in by sun evening. Strong
agreement across GFS/European model (ecmwf) with regards to the early evolution and
structure of the front...but GFS is trending a bit slower at this time.
Will carry chance probability of precipitation along the front with a general blend for
Aviation /02z Tuesday through Saturday/...
VFR conditions for the remainder of the evening. Deteriorating
conditions with a period of showers overnight...accompanied by MVFR
stratus. Stratus will hang on for a few hours behind the front
Tuesday morning. Deeper moisture looks to allow for IFR at kfkl
and kduj late tonight/Tuesday morning. Winds will become northwest
overnight under 10 kts.
Outlook...Tuesday night through Saturday...
VFR conditions expected in genl with possiblity of restrictions Tuesday night
owing to vlly fog.