Area Forecast Discussion
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FXUS61 KPBZ 050131

Area Forecast Discussion
National Weather Service Pittsburgh PA
831 PM EST Sun Dec 4 2016

Some locations in the higher elevations are expected to receive
freezing rain tonight. An unsettled weather pattern will continue
through the week, with much colder air arriving by Friday.


A rather sharp short-wave trough is advancing eastward into the
region this evening with widespread isentropic ascent allowing for
a vast shield of stratiform precipitation to develop ahead of it,
especially north of I-70 in Ohio. Along the southern edge of this
precipitation shield, radar imagery has generally started to trend
toward a more curious reflection of dynamical processes going on
in the atmosphere. The striated depiction of echoes mostly from
near Zanesville to Pittsburgh points toward CSI, as does the
synoptic positioning relative to the upstream system with the
upper jet curving overhead. Model cross sections do reveal an area
of negative theta-e lapse rates with respect to geostrophic
momentum in this area, so enhanced precipitation rates will be
likely along the southern flank of the precipitation shield as a
result. As this area moves northeastward, it is also starting to
get into a slightly colder column. The 00z KPBZ sounding revealed
an utter chasm in dewpoint depressions off the ground, which with
varied precipitation rates due to more unstable processes going on
has resulted in periods of sleet mixed in with the rain. Sleet was
thus added to the grids with the unstable precipitation moving
northeastward this evening.

Farther north, model soundings reveal wet bulb temperature
profiles that should be conducive to a period of snowfall for
several hours tonight before warm advection gradually warms the
lower portion of the profile too much to allow for continued
snowfall. Additionally, mesonet observations especially in
Forest and far northern Venango and Jefferson County reveal
surface wet bulb temperatures straddling freezing. Thus, while the
ground is not frozen, grassy surfaces now seem poised to pick up
as much as a slushy inch in the aforementioned locations. While
other areas south of here may see snow in the air, accumulation
still seems unlikely.

In the ridges, temperatures are trending from the mid 20s to mid
30s in Tucker and Garrett counties at this hour with some penchant
for additional wet bulb cooling. However, due to a farther
southward placement, warm advection off the deck should preclude
much in the way of snowfall here. That said, freezing rain or even
a touch of sleet will certainly be possible in these areas, thus
the previously issued advisory has been left in effect for icing
considerations. Temperatures will continue to be monitored over
the Chestnut and Laurel Ridges to determine whether a headline
expansion into these areas is warranted.

Eventually by morning, flow should start to turn southwesterly,
warming all areas including the stubbornly cold Garrett County to
rainfall, however several hours of wintry precipitation will be
likely before we reach that point. Fries


Clouds will stream back in Monday night in advance of a low
pressure system that will move across the region. As precipitation
moves in Monday night and Tuesday morning, many places could have
a brief period of freezing rain before warm advection changes all
precipitation over to rain by Tuesday afternoon. Have continued
with categorical pops through this time period, with rain changing
over to snow as it wraps up late Tuesday night into Wednesday.
High temperatures in the low to mid 40s on Tuesday will likely be
the warmest readings of the 7 day forecast.


Yet another system moves through Thursday, with a cold front
bringing another chance for precip. Most of this precipitation
would likely fall as snow, and behind the front temperatures will
plunge into the teens by Thursday night. Cold advection should
then prompt snow showers to continue through Saturday morning.
Temperatures will struggle to recover, but another cold front will
approach from the west Sunday.


A quick moving low pressure system will cross the area tonight
spreading MVFR to IFR ceilings from west to east overnight. Despite
temperatures currently in the mid to upper 30s, dewpoint depressions
in the low-levels will allow temperatures to drop low enough to
support some snow at least mixing in with rain at the onset of
precipitation tonight.

MVFR stratocu is then expected to persist into the afternoon given
the cold flow off the Lakes in the wake of the surface front. At
least some clearing should then take place late in the day Monday.

More restrictions are likely with, and in the wake of Tuesday low
pressure. More restrictions will follow with a strong late week
cold front.


MD...Winter Weather Advisory until 4 AM EST Monday FOR MDZ001.
WV...Winter Weather Advisory until 4 AM EST Monday FOR WVZ514.


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