Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Pittsburgh PA
1222 PM EST sun Feb 7 2016
low pressure is poised to spread rain and snow over the region on
Monday and Tuesday.
Near term /through tonight/...
middle level cloudiness has rapidly dissipated undr shortwave ridging...no
other changes were needed for the near term period.
The upper Ohio region is expected to remain dry through midngt with
ridging ridging between western Great Lakes and southeastern coastal low
pressure systems. Temperatures will once again be above seasonal
The western low will be the problem for the next few days as it is
forecast to deepen over the Midwest and plague the are with broad
ascent...deep moisture...with shortwave support rotating around the
For tonight...moisture and ascent via warm advection and weakly
divergent flow aloft are likely to support precipitation
development over western zones toward morning...with eastward
progression after daybreak Monday as per slower model consensus. As
that solution seems reasonable given subsidence on the western flank of the
exploding southeast coast/western Atlantic low...have adjusted grids for that
scenario and retreated from overnight probability of precipitation.
Precipitation type remains an issue given the aforementioned warm advection
and lingering boundary layer warmth. Expect a snow-to-rain or a
primary snow situation with melting at the surface as the systems cold
front ploughs toward the I 77 corridor during the predawn hours.
Given the temperature limitations and slower progression...any light
accumulation is not expected to be problematic.
Short term /Monday through Wednesday/...
the marginal temperature profile and warm boundary layer on the eastern
side of the system are likely to continue compromising snow
potential and preclude much in the way of accumulations through
Monday. However...the systems frontal passage will usher in a colder
airmass Monday night and any lingering rain showers...or rapidly
melting snow showers...will have better accumulation potential as
Fortunately...the encroachment of the middle/upper low center should
sufficiently weaken the wind/frontogenesis potential and overall
ascent fields to offset the improved temperature profile for
snow. The forecast remains of prolonged snow shower potential
through Tuesday with relatively minor accumulations. The
exception...as always...will be the ridges...where orographic
support should promote more significant accumulation.
By Wednesday...the cutoff low is forecast to be filled/phased with
the upper Ohio under the axis of a high-amplitude eastern Continental U.S. Trough.
Snow shower potential will thus continue as increasingly colder
air is poised to flow over the region as that axis shifts eastward. In
addition...the latest deterministic trend is to rotate a vorticity
center/shortwave into the base of that low. Precipitation probs were thus
incrsd for Wednesday...cumulating in categorical numbers for the
higher elevations...but dry advection and increasing cold in the
snow-source region should degrade efficiency so totals were not
amped much at this stage of the forecast process.
Long term /Wednesday night through Sunday/...
the aforementioned upper troughing portion is prognosticated to continue
funneling cold air over the area through the weekend. Sub average temperatures
can be expected with readings 10 to 15 degrees under the normals
likely by the weekend. The I 80 corridor and ridge zones will have
the better snow shower potential during this period given the
cold...off-the-lakes upsloping flow.
The long term was constructed using the superblend guidance.
Aviation /17z Sunday through Thursday/...
VFR will continue today although middle level clouds will increases later ahead of
an approaching cold front. MVFR/patchy IFR in rain and snow is
expd for ports west of pit by sunrise Monday morning...with precipitation/condition
deterioration spreading east through the day as the front advances.
Outlook.../Tuesday through Friday/...
restrictions can be expected through Thursday with the area undr upper