Saturday, December 16, 2017, 9:18 PM EST
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Area Forecast Discussion
Valid At
Wed, Dec 31, 7:00pm EST
FXUS61 KPBZ 162322

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

Another upper level disturbance will approach Sunday afternoon
to increase precipitation chances. Warmer temperature can be
expected for the coming week.


The early eve update featured a quicker ending to residual light
snow for areas north of Clarion given radar trends in the wake
of the supporting jet streak.

Otherwise, building high pressure will support a quiet night
with ensuing warm, relatively moist advection holding lows a few
degrees above the seasonal averages. No changes were needed for
that portion of the forecast.

An upper shortwave will approach Sunday afternoon and increase
light precipitation chances, but warm advection is expected to
support rain, possibly a mix for counties north of Pittsburgh.
Surface temperature is expected to be warm enough that no
problems are anticipated.


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.


For FKL and DUJ, MVFR ceilings will linger through most of the 
period as clouds remain in vicinity of a stalled frontal
boundary. Otherwise, building high pressure will ensure VFR. 

Condition deterioration can be expected by Sunday evening as
another disturbance spreads light precipitation over area

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





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