Area Forecast Discussion
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FXUS61 KPBZ 162007

Area Forecast Discussion
National Weather Service Pittsburgh PA
307 PM EST Sat Dec 16 2017

Snow ends north of interstate 80 this evening. The next upper
level disturbance approaches Sunday afternoon with increasing
rain chances, though some snow may mix in Sunday night. Temperatures
will moderate to above seasonal averages through the beginning
of the week.


Area of convergence along a lifting boundary continues to
support some light snow north of I-80. Expect this to move
north and dissipate through the rest of the afternoon as high
pressure builds to the south. Little additional accumulation is

Building ridge will lend to a quiet night tonight. Warmth aloft
should hold temperatures up slightly, given mostly clear skies
and light wind - though it doesn`t appear we will fully
decouple. Stayed close to persistence for lows.

Next system will approach Sunday afternoon, though this is all
mid-level driven as shortwave lifts across the upper Ohio
valley. Light precipitation will spread across the region
through the evening but warm advection in advance of the system
should support mainly rain. A mix is possible to our north,
where temperatures may lag a bit with lingering cloud cover. For
now, with consideration to the differences in the model
profiles, will continue to mention a rain/snow mix though there
may be a brief window for freezing rain. Current thinking is
there should be enough daytime heating to warm surfaces and
limit this potential.


Shortwave will depart quickly to the east Sunday night, leaving
nearly zonal flow aloft and some uncertainty to boundary
placement through the period as additional weak shortwaves pass.
With no considerable lift apparent in the guidance but plenty of
moisture, expect mostly cloudy conditions and very light
precipitation. At this point, profiles are not even well
saturated above the boundary layer which suggests little more
than drizzle through this time frame. Made only modest
adjustments to the PoPs through the short term to reflect some
of the newer guidance but generally think chance is appropriate
given the likelihood of drizzle versus measurable rain.

Despite expected cloud cover, warm advection should lead to
temperatures at least near seasonal averages.


A broad trough will drop into the central CONUS Tuesday night
sweeping a cold front through the area. This could re-invigorate
showers Tuesday night into Wednesday, but will help drive
temperatures back to near-normal values. Upper-level flow
returns to zonal behind the front, bringing a drier and warmer
trend until the latter part of the week. Models still have
another system/cold front for Friday, but strength and
placement of the low have changed with newest guidance. Will
hold close to the SuperBlend for precipitation details, and look
for clarity in the coming guidance packages.


Near and north of I-80, MVFR ceilings will linger through most
of the period as clouds remain locked in. Snow showers may still
produce brief MVFR/IFR visibilities until mostly shutting off
by 00Z. Ceilings may drop to IFR during the overnight/early
hours for a period before lifting by mid-morning once mixing
kicks in.

Further south, building high pressure will keep conditions VFR
through the period. Mid clouds will mostly clear out this
afternoon, with scattered clouds at most tonight. Overcast
conditions may return by midday Sunday ahead of a weak
disturbance, with most light precipitation holding off until
after 18Z.

Restrictions are possible from Sunday night through Tuesday, as
abundant low-level moisture may become trapped underneath an
inversion for an extended period. IFR conditions are possible at




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