Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Pittsburgh PA
919 am EST sun Feb 14 2016
moderating temperatures will continue. A moisture-laden system
will approach for Monday night. A wintry mix will be possible in
Near term /until 6 PM this evening/...
little change to the forecast for this afternoon...with minor
tweaks to sky cover and temperatures. The remaining Wind Chill
Advisory was allowed to expire.
Abundant sunshine will start the day before high clouds start to
filter in from the west. Surface flow will slowly turn southeast
through the day with slow moderation in temperatures as a result.
That said...high temperatures will still struggle to reach the
upper teens in many places as high albedo new snow cover and a
weak middle February sun will likely have difficulty overcoming
morning lows near zero.
Short term /6 PM this evening through Tuesday/...
several successive waves will keep the area rather unsettled
through early in the week. Isentropic ascent begins over the area
on Monday as a northern stream wave moves through the Great Lakes.
Model quantitative precipitation forecast is exceedingly light with this system...however good
saturation is noted in the 285-295k layer with condensation
pressure deficits dropping decidedly below 10 mb for much of the
day. This coincides with a saturation of the dendritic growth
layer...however boundary layer relative humidity values below it are rather
anemic. The result will seemingly be efficient snow growth with
abundant sublimation in the boundary layer. With light quantitative precipitation forecast...the
net result seems to be general light snow on Monday with far less
than an inch possible most everywhere.
Another deeper wave rides through the middle Atlantic Monday night
into Tuesday. The model consensus has shifted decidedly west with
the low level reflection of this system. Most guidance now tracks
the 850 mb low through eastern Ohio or up the northern Panhandle
of West Virginia. As a result...an all snow forecast seems like an
impossibility. Model soundings suggest a period of sleet and
freezing rain after initial warm advection snow
develops...however the duration of time the boundary layer would
remain cold enough is far from certain. Screaming 850 mb flow from
the southwest into the ridges and metropolitan Pittsburgh suggests the
period of icing may end up being lower in duration than one would
think given we are sitting at zero degrees right now.
However...ground temperatures are likely very cold and will be
very cold at the onset of the event. Thus...freezing rain wording
was used in a fairly heavy- handed fashion through the forecast.
Given model waffling and trends...it would seem most areas would
see a couple inches of snow...before some ice...and many areas
south of Pittsburgh and even in the ridges would go all rain
overnight Monday night. Given that none of the parameters are
likely to meet warning criteria in and of themselves...no watches
have been issued. Additionally...given that model trends have been
anything but in unison...confidence is not anywhere near high
enough to issued advisories at this early juncture. Thus...severe weather potential statement
wording has been maintained and further scrutiny can be given by
further shifts with regard to snow/ice/rain potential. Fries
Long term /Tuesday night through Saturday/...
a second weak low will cross Tuesday night with warm advection
continuing. Again...p-type issues remain with rain and snow
changing to snow with cold advection Wednesday with the systems
departure. Appears any precipitation with this low will be light.
Ridging and a warm up looks to take place by late in the period.
Heavy emphasis was used on the superblend for the long term.
Aviation /14z Sunday through Thursday/...
a general VFR forecast for all ports through the day. There are
still streamers of lower clouds moving off the lakes...so a brief
restriction in MVFR clouds can't be ruled out...but it is very
difficult to pinpoint this. Have decided to include a mention
early of MVFR restrictions at fkl and duj.
After sunrise...the Arctic air will finally begin to slowly recede
to the northeast allowing for a decrease in overall cloud cover
in the same direction. Area of middle cloud will overspread from the
west late in the day.
Outlook.../Sunday night through Thursday/...
low pressure systems will bring widespread restrictions later
Sunday night through Wednesday.