Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Pittsburgh PA
113 PM EST Wednesday Dec 18 2013
building high pressure will gradually end snow chances over the
region today. Warmer temperatures and rain chances can be expected
by the weekend.
Near term /through Thursday/...
snow showers and flurries have really begun to wane as of the last
hour and this is expected to continue through the afternoon as the
midlevels dry out. Still anticipate a break-up in the cloud cover
by late this afternoon but this may have little impact on warming
temperatures with the sun setting in a few short hours. With this
in mind...have lowered highs for the remainder of the day.
High pressure will build eastward tonight and tomorrow...keeping
the region dry. Despite the clearing skies and residual snow
cover...temperatures overnight may not drop off too much. This is
in part due to the strong warm advection that will be taking
place aloft. The question is whether the low levels will
decouple...allowing for temperatures to fall at all or if low level
mixing will actually allow for temperatures to remain stable or
Temperatures Thursday however will be greatly impacted by the
strong southwesterly flow and warm advection that will be
experienced. Highs were forecast to be 5-8 degrees above normal
for this time of year.
Short term /Thursday night through Saturday/...
high pressure will maintain the dry weather through Thursday night while
warm advcnt in advance of a northern plains trough spprts warmer temperatures. Precipitation
chances in the form of rain will increases on Friday though as incrsg moisture
via southwesterly flow interacts with an eastward sliding frontal boundary.
No model is indicating any consistent depth to that moisture supply
though...hence probability of precipitation were limited to likley numbers for now and quantitative precipitation forecast
on Friday is expected to be light. However...given the incrsd surface
wind and rising dewpoints...snow melt in the ridges may prime the
Monday basin for river rises during the weekend.
Long term /Saturday night through Tuesday/...
amplified upper flow portion via phasing of a southern stream low with the
aforementioned northern plains trough is forecast to maintain warm temperatures
over the upper Ohio region into the weekend...at the price of continued
rain chances. Frontal boundary positioning and middle level moisture tap undr
this scenario are qnable as per differences in the latest European model (ecmwf)
and more progressive GFS...thus probability of precipitation were limited to a
collaborated likely forecast for the weekend...and temperatures were
hedged for potential precipitation. Nevertheless...river rises should be
anticipated via precipitation...and/or snow melt.
Shortwave in southwesterly flow is expected to decisively pull the front
through later Sunday or Monday...thus ending the late autumn
Aviation /18z Wednesday through Monday/...
MVFR conditions will continue for a few more hours this afternoon
as dry air finally ends the lingering snow showers and breaks up
the cloud deck. This should happen first at zzv and expand
northeastward. VFR conditions should return all sites this
evening...with gusty southwest winds tapering off.
However...continued the mention of low level wind shear as a
strong low level jet will move across the region.
Wind gusts should pick up after daybreak again tomorrow.
Outlook.../Thursday night through Monday/...
rstrns are likely Friday through sun as a slow moving frontal system
afcts the region bringing rain showers. Lingering restrictions may
continue into Monday in northwest flow.