Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Pittsburgh PA
346 PM EDT Friday Mar 14 2014
a cold front will cross the region overnight into Saturday
bringing a period of rain and snow showers. Low pressure
developing over the Central Plains will move northward towards the
region Sunday...bringing wintry precipitation Sunday night and
Near term /through Saturday/...
wind will continue to remain gusty out ahead of the cold front
that crosses overnight. Have made very few adjustments to the
timing of the front as all of the hi res models have precipitation
reaching pit by 06z. Still think the bulk of the precipitation
will fall as rain as the cold air looks to lag behind the frontal
passage. A rain-snow to snow changeover will occur further north
but only very light snow accumulations are expected since the
ground will a bit warmer from the daytime warm temperatures.
Cold front will slowly sag southward across the region on
Saturday. While the midlevels will dry out relatively
quickly...some lingering boundary layer moisture may provide for a
few rain or show showers early Saturday morning in west-northwest
flow. This will be mainly north of I-80. However...the moisture is
most likely to manifest itself in a scattered stratocu deck
through the afternoon.
Short term /Saturday night through Monday/...
the next weather system is prognosticated to approach the region Sunday.
As has been the case several times this winter...the models have
not been consistent in the placement of this system as it
approaches...which has huge implications on the precipitation
amounts that we could expect. That being said...there is enough
confidence that precipitation will occur to have categorical probability of precipitation
and...with an Arctic high in place over Canada...most of the
region would see primarily snow for the event. However...there is
a bit of uncertainty in the precipitation types as you go south
towards the PA/WV border...depending on the location of the 850hpa
low and the warm tongue of air associated with it.
As the previous forecaster had mentioned...there are several
variables that go into the development of this system and its
eventual track and strength as it approaches. The models keep
suggesting the phasing of both a subtropical and polar jet aloft
as well as some strong Omega present in the dendritic growth
zone...suggesting someone could see some high snow accumulations.
Working against the longevity in the event is the fact that all of
the models keep the system a progressive wave. And...snow that
initially falls in the late afternoon Sunday will have the
middle-March sun to content with...so snow ratios were kept rather
Until the models can get their act together...it's hard to
pinpoint exactly where the higher snow accumulations could be. While
the overnight GFS runs suggested a more northern track and extent
in precipitation...the new GFS has suppressed this a bit to the
south...closer to the last two runs of the European model (ecmwf). With this in
mind...will continue to mention the accumulating snow in the
hazardous weather outlook.
The system should quickly depart to the east as the surface low
redevelops on the coast. Temperatures were kept at a blend of
guidance values...with highs remaining below normal.
Long term /Monday night through Friday/...
behind exiting system drier air works into the region for Monday
night and Tuesday with below normal temperatures. Next system
arrives with rain showers arriving ahead of another cold front
later Wednesday and continuing into Wednesday night. As front
passes Wednesday night looks to be a changeover to snow showers
late but nothing significant. Below average temperatures for late
week with scattered rain or snow showers in northwest flow aloft.
Aviation /19z Friday through Wednesday/...
VFR can be expected through the taf period. Winds will continue to
gust over 25 kts until sunset this evening. A fast moving cold
front will bring light rain showers tonight with ceilings expected top
drop to MVFR behind front only across northern terminals kfkl and
kduj. Low pressure across eastern Canada will allow for gusty
winds over 20 kts Saturday.
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.
General VFR Tuesday into Wednesday morning.