Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Pittsburgh PA
1236 am EDT Monday Oct 20 2014
shower chances and cold temperatures will continue until upper low
pressure shifts eastward later this week.
Near term /through tonight/...
Post midngt update feature adjustments to cloud and temperatures based on
the latest observational and model trends. In genl...warm advection and
incrsg cloud cover will preclude much more of a temperature drop this morning.
Frost advisory for the cnties surrounding Morgantown will remain in
effect until the clouds and surface wind over that area increases.
Otherwise...the approaching shortwave...with trough axis over Lake Superior early
this morning...is still expected to generate showers over the upper Ohio region
by evening. Likely to categorical probability of precipitation have been continued...but ovrall
numbers were tempered and timing adjusted for a later start given the
depth of the dry layer on the evening snding as well as the latest model
Morning temperatures were forecast using hrly lamp guidance and rap numbers...while
cool daytime highs were tweaked using GFS mosguide trends.
Short term /Tuesday through Thursday/...
a jet streak moving through the western flank of the eastward shift upper trough
is prognosticated to carve a cutoff low over the upper Ohio Valley region by
late Tuesday. Cooling middle levels with that system will lower convective
thresholds and spprt shower activity through midweek...with particular
emphasis over upslope regions to the north and east of Pittsburgh.
By Thursday...model world projects sufficient coastal development/deepening
to diminish probability of precipitation over the immediate area...but confidence in shortwave/vorticity
projections through the western flank of the system is minimal...so
have held at least slight probability of precipitation over the ridges through Thursday.
Long term /Thursday night through Sunday/...
eastward progress of the aforementioned upper low should ensure a dry and
seasonally cool close to the week. Tweaked wpc numbers were used to
represent the long term period.
Aviation /04z Monday through Friday/...
VFR conds are expd with increasing ac/cirrus through today ahead of an approaching
shortwave. This shortwave and associated cold front is expd to bring MVFR
conds and increasing shower chances this evening and overnight.
Aviation /Tuesday through Friday/...
periodic rstrns are possible through middle weak as an upper low drifts across the
WV...frost advisory from 5 am to 9 am EDT this morning for wvz012-