Area Forecast Discussion
Issued by NWS

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FXUS61 KPBZ 100415
AFDPBZ

Area Forecast Discussion
National Weather Service Pittsburgh PA
1115 PM EST Fri Dec 9 2016

.SYNOPSIS...
Cold northwest flow will continue a few bands of snow showers into
Saturday. Low pressure will bring accumulating snow Sunday, mixing
with and changing to rain later Sunday night and Monday.

&&

.NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
Low level flow has turned decidedly southwest, bringing in some
drier air in the lower levels. however, flow up toward 850 mb
remains stubbornly northwesterly with model indications revealing
little trend toward any more westerly or southwesterly component
at this level over the next six hours or so. Luckily, this is
leaving us with a fair amount of directional shear in the lower
levels of the atmosphere, preventing a true dominant band of snow
downwind from Lake Erie. However, given that northwesterly flow
remains in the most unstable portion of the column which is also
co-located with the dendritic growth layer, it seems the current
radar depiction over Mercer and Venango Counties will likely
linger for several more hours. It seems reasonable thus given snow
rates over the past few hours to expect around two more inches of
snow in the more decent lake effect bands over northern Mercer and
Venango County through the night. The lake effect snow advisory
was thus extended until 5 AM.

Elsewhere, flurries will be possible as somewhat unstable lapse
rates remain even with a much drier column. Fries

&&

.SHORT TERM /6 AM SATURDAY MORNING THROUGH MONDAY/...
High pressure will begin to move east Saturday with flow becoming
westerly as weak shortwave exits. Temperatures will continue well
below average.

Complex low pressure will approach Sunday and move across the
Great Lakes Monday. Warm advection snow will develop across the
region Sunday and continue into Sunday evening, before mixing
briefly with freezing rain and then changing to plain rain except
for areas north of I-80 where cold air will hang in until mid
morning Monday. With surface low so far west, warm air should be
able to move north fairly quickly, keeping snow accumulations in
check for the most part. Best estimate for now is 4-6 inches north
of SR 422 in PA, with only an inch or two across Pittsburgh. Areas
south of Pittsburgh will have little in the way of accumulation.
Some light icing possible mainly in the ridges for a time Sunday
night. Warm advection will push temperatures into the upper 30s to
mid 40s Monday before a cold front drops temperatures back toward
normal in the afternoon.

&&

.LONG TERM /MONDAY NIGHT THROUGH FRIDAY/...
Main feature will be an arctic cold front Tuesday night crossing
east of the ridges early Wednesday. Temperatures will be 15 to 20
degrees below average through late week. While snow showers will
be scattered mainly across the north, no significant snow is
expected.

&&

.AVIATION /04Z SATURDAY THROUGH WEDNESDAY/...
Broad upper troughing will maintain mainly MVFR conditions
for most locations outside of FKL and DUJ where scattered snow
showers will result in continued IFR. Improvement to VFR by
Saturday afternoon as high pressure briefly builds in.

.OUTLOOK...
Widespread restrictions are likely Sunday and Monday, and again
Wednesday, with crossing areas of low pressure.

&&

.PBZ WATCHES/WARNINGS/ADVISORIES...
MD...None.
OH...None.
PA...Lake Effect Snow Advisory until 5 AM EST Saturday FOR PAZ007.
WV...None.

&&

$$



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