Area Forecast Discussion
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FXUS61 KPBZ 140205

Area Forecast Discussion
National Weather Service Pittsburgh PA
905 PM EST Thu Dec 13 2018

Rain chance will increase on Friday and persist through the
weekend with the approach and passage of low pressure.


The late eve update featured adjustments to temperature as areas
that have briefly cleared dropped off rapidly via radiation with
a light wind.

Otherwise, no major changes were needed as ridging on the van
of strong, Mississippi Valley low pressure will suppress precip.
chances through daybreak Friday. Expect low temperature 5 to 10
degrees above the average under increasing cloud cover and warm
advection above the boundary layer.


The aforementioned strong, closed upper low will drift slowly
newd as it attempts to phase into the stronger wly flow across
the nrn CONUS. Its slow movement will preclude any precipitation
onset until at least mid-day Fri, so concern for any wintry
precipitation at the onset is abated.

Modest warm-air advection over esely sfc flow will support the
development of broad coverage of light rain starting Fri
afternoon, with best chances to the south of Pittsburgh and
especially along and near the ridges.

There may be a brief lull in rain showers on Sat morning as the
upper low begins to eject newd, but increasing coverage is
expected by Sat afternoon and evening as the low approaches,
ely low-level flow increases and upward motion is enhanced. Rain
rates are expected to remain quite manageable, so no flood
threat is anticipated.

With warm advection quite strong, and model-blend bias
correction tuned to the tenacious cold spell of the last two
weeks, blend temperature predictions likely under-represent the
impending warmth, so temperature was bumped upward from default
blended guidance for Fri and Sat.


Ensembles show some spread with the track of the ejecting upper
low beginning on Sun, but most move it off the Mid-Atlantic coast
by late Sun. Compared to prior days, Sun-Sun night will be
relatively dry, although the day may start rainy as the upper
low vacates. Residual occasional showers may linger into Sun

A shortwave trough and cold front will renew lake-enhanced rain
and snow showers Sun night and Mon as cold air advances sewd.
Building high pressure will bring dry weather Tue and Wed, with
temperature moderating toward seasonal average.


General VFR, marred only by mid level clouds and lingering
stratocu early, is expected into mid Friday as an upper ridge
slides across the region.

Condition deterioration is expected on Friday aftn and eve though
as low pressure emerging from the Lower MS Valley shunts a
broad swath of moisture over the Upr OH.

Widespread restrictions with periodic rain are expected to persist
through the weekend as that low pressure system crosses.




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