Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Pittsburgh PA
646 PM EDT Friday Mar 14 2014
a cold front will cross the region tonight bringing a period of
light rain and light snow. A crossing disturbance is likely to
spawn some snow on Sunday and Monday.
Near term /through Saturday/...
early evening update featured adjustments to probability of precipitation and weather wording as
apprchg cold front is plowing into a rather dry airmass. Light wording
was thus included as well as a mild reduction in measurable precipitation
probability based on a blend of the latest higher res guidance.
The front will complete passage across the region early on
Saturday...but lingering middle level thermal trough with some surface
relative moisture may spprt a few rain or show showers on Saturday
morning in the west-northwest flow. Otherwise...conditions will be dry for the
majority of the region and temperatures will recover close to the seasonal
Short term /Saturday night through Monday/...
another more potent...but progressive shortwave is prognosticated to approach
the region Sunday...and complete passage on Monday. Models have been
inconsistent in the placement and magnitude of this trough...especially
in conjunction with potential phasing of southern stream flow...which
would have implications on the dynamics of the precipitation spprt.
Nevertheless...confidence is sufficient to forecast categorical probability of precipitation
over areas south of I 80 into Sunday night. With an Arctic high
projected to sag over the Great Lakes...most of the region would
see primarily snow for the event...although middle March boundary layer
warmth may retard intial accumulation on Sunday afternoon...especially
over southern zones where precipitation is more probable...and where warm advection
above the surface might spprt a mix for a few hours.
Of particular interest in the model world is the difference in the
Omega fields as projected by GFS and NAM today. NAM apparently
once again is exploding its precipitation prognosis due to the overheated
warm advection dynamic...while GFS values are much more reasonable.
At any rate...accumulating snow was forecast for the region...but
totals are currently expected to remain undr warning thresholds for
all but the highest elevations. Due to the aforementioned
factors as well as collaborative hesitations...have abstained from
issuing a watch for those zones today. Middle shift will have a look at
the next round of solutions and likely have a more decisive answers.
Long term /Monday night through Friday/...
in the wake of the exiting system...drier air is projected over the
region alng with sub normal temperatures. Another shortwave is forecast to
spread showers once again by Wednesday. Northwest flow is thereafter prognosticated
to spprt continued cool temperatures and chance probability of precipitation.
Aviation /22z Friday through Wednesday/...
surface wind will continue to gust toward 30 knots this evening as a cold front apprches
the area. That front is likely to spawn some light rain...light
snow...and eventual MVFR with passage tonight. Improvement can be
expected Saturday...although tight pressure gradient will maintain gust
potential near 20 kts.
Outlook.../Saturday night through Wednesday/...
the next chance of genl restrictions will come with northern flank precipitation of low
pressure crossing the middle Atlantic region on Sunday into Monday.
Another disturbance may spawn showers and restrictions later on Wednesday.