Scientific Forecaster Discussion
fxus61 kpbz 120432 aac
Area forecast discussion...updated
National Weather Service Pittsburgh PA
1132 PM EST Mon Nov 11 2019
rain will change to snow tonight with the passage of a cold front.
Periodic snow showers should continue Tuesday with an upper level
disturbance before building high pressure returns dry weather
Near term /until 6 am Tuesday morning/...
rain should continue to change to snow from northwest to southeast behind the
passage of a cold front, as deep layer moisture and upper divergence
maintain the precip. Most locations should see less than an inch of
snow, though areas in the higher terrain and north of I 80 can expect 1-2
inches. Will maintain the Winter Weather Advisory as is, with
additional snow expected in these areas Tuesday. The synoptic snow
should taper off by morning as deep layer moisture and initial upper
support exit ewd. Lows should be around 5-10 degrees below average.
Short term /6 am Tuesday morning through Wednesday/...
by Tuesday morning, most snowfall associated with the frontal system
will have cleared the County Warning Area. Strong cold air advection of an Arctic
airmass will be underway, leading to a very cold (potentially record-
breaking) subsequent 48 hours across the forecast area, with lake-
enhanced showers persisting through the first half of that period.
Strong northerlies carrying -15 to -16 degrees celsius air at 850mb
over a ~10 degrees celsius Lake Erie will create steep lapse rates,
yielding cape in excess of 500 j/kg. This will promote robust and
fairly widespread lake-effect / lake-enhanced convection into the
area through much of Tuesday.
Between the frontal precipitation and subsequent lake-enhanced
snowfall, accumulations of around an inch are to be expected area-
wide. The outer snowbelt counties near/north of Interstate-80 may
receive between 2 and 6 inches, while the higher elevations from The
Laurels south through West Virginia will likely receive between 2 and
4 inches. Therefore, a Winter Weather Advisory has been issued for
these counties tonight into tomorrow. A few bands of isolated higher
amounts throughout the County Warning Area are possible with some of the more robust
snow streamers that mesoscale models are hinting at. Due to low
confidence in exact placement, have went with a general north to
south gradient (and elevation gradient) in snowfall accumulation,
ignoring any possible mesoscale snow streamers.
Shower coverage will decrease Tuesday night as the upper trough axis
passes and high pressure builds into the lower levels. The resultant
backing of wind from northwest to west will quickly end snow shower coverage
for the County Warning Area.
Highs on Tuesday will struggle to reach 30 before dropping into the
teens by Wednesday morning. A few cities may break or tie their
record daily low temperature.
Cold weather will continue on Wednesday as the low-level ridging
becomes centered across the County Warning Area. Expect another day where the
temperature remains below the freezing mark W/ increasing upper
clouds moving in from the west.
Long term /Wednesday night through Monday/...
another quick-moving shortwave will move north of the region
Thursday. With the path of the wave and a dry atmosphere in place,
appears any light snow showers will remain north of the region.
Looking ahead, temperatures will gradually moderate as the synoptic-
scale wave pattern becomes less amplified. The next chance of
widespread precip will likely be at the end of the weekend or early
Aviation /06z Tuesday through Saturday/...
IFR to LIFR conditions for the early part of the forecast as an area
of snow quickly moves through the region. All ports, with the
exception of mgw, will be snow to begin the forecast. Mgw will
quickly transition over within the first hour or so.
A break in the snow and an improvement to MVFR cigs is expected at
all ports as dawn approaches. Vis should improve as well, although
fkl may hold onto lower vis as snow showers begin to stream from Lake
After Dawn Lake-enhanced snow showers will become the focus and may
bring periods of reduced visibility; however, confidence is too low
at the moment to pinpoint which sites and time-frame specifically.
with building high pressure Tuesday night into Wednesday, VFR
conditions shall return. Fkl may experience restriction until
Wednesday night if lake-enhanced snow showers prevail.
Maryland...Winter Weather Advisory until 7 PM EST Tuesday for mdz001.
PA...Winter Weather Advisory until 7 PM EST Tuesday for paz007>009.
Winter Weather Advisory until 7 PM EST Tuesday for paz074-076.
WV...Winter Weather Advisory until 7 PM EST Tuesday for wvz510>514.