Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Pittsburgh PA
545 am EST sun Dec 28 2014
a cold front will be accompanied by showers this morning. A
return to below-normal temperatures will start Monday.
Near term /until 6 PM this evening/...
only changes needed for the pre dawn update were tweaks to hourly
weather grids and aviation.
front will move into the middle-Atlantic region this
morning and showers will end across most of the region early this
afternoon. A weak upper level will move eastward to the north of
the slowing boundary and will keep in the risk for showers through
the rest of the day in the far southeast. Cold air advection will trail behind
the boundary... so expect steady or slowly falling temperatures. The
colder air will reach the southeastern ridges this
afternoon...which will allow for a mix of rain and snow or all
snow across the ridge tops.
Short term /6 PM this evening through Tuesday/...
broad high pressure will build into tonight and hold steady
through Monday. The next shortwave trough on Monday will provide
another push of colder air. Modest wind flow aloft...which will
veer to the northwest will accompany the cold air advection...however...strong
subsidence from high pressure and low inversions...well below snow
growth zone...should prevent any lake/orographic snow.
Model differences begin Tuesday...concerning impacts of coastal
low. NAM/sref remain most aggressive...showing a much more
energetic northern wave...spreading precipitation further north then
latest GFS/ECMWF/gefs. Latest run of the NAM has moved toward the
drier model runs...leading ME to believe that a drier forecast is
the way to go. Will leave in schc/chance probability of precipitation in the southeastern
ridges for snow showers.
A push of Arctic air will commence late Tuesday.
Long term /Tuesday night through Saturday/...
the extended will largely be dry with a decreasing trend in
temperatures as a broad trough in the longwave pattern slowly sags
south across the eastern Continental U.S..
Potent shortwave trough expected to impact forecast area Friday night and Sat. Both
GFS and European model (ecmwf) show temporal consistency...although the exact
track of the system differs. Regardless...the surface feature passes
to the northwest of the forecast area...leading to strong warm air advection
that should keep precipitation liquid. Only caveat will be sub-freezing
temperatures at onset...which could spell a freezing rain scenario for areas
that typically retain cold air...especially sheltered vllys in ridge
counties and northern zones. Probability of precipitation were increased day 7 given expected measurable
precipitation...but uncertainty remains in precipitation type.
Aviation /12z Sunday through Thursday/...
rain and IFR ceilings will give way to MVFR stratocu today...with eventual
VFR develop from the west with subsidence and dry advection. The exception will be
northern terminals where cold flow over the lakes is expected to continue
fueling MVFR stratocu into the evening.
Outlook.../Sunday night through Thursday/...
periodic restrictions can be expected for the first half of the
week with cold advection and crossing disturbances.