Area Forecast Discussion
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854
FXUS61 KPBZ 090537
AFDPBZ

Area Forecast Discussion
National Weather Service Pittsburgh PA
1237 AM EST Fri Dec 9 2016

.SYNOPSIS...
Periodic snow showers are expected into the weekend, especially
north of Pittsburgh. All locations are likely to receive
accumulating snow on Sunday.

&&

.NEAR TERM /UNTIL 6 AM THIS MORNING/...
Minor changes to the overnight forecast. Area webcams confirm, for
the most part, that accumulations thus far have been less than an
inch, with most areas only receiving a dusting. Did up PoPs a bit
along the southeast ridges, into the likely range, given ongoing
activity at 2G4 and surrounding areas. Temperatures in good shape
overall.

The overall forecast for the next 24-36 hours looks to be in good
shape at first glance, but will reevaluate with new model data. In
particular, there are still some indications that Forest County
could fall under a favored lake effect band during the day Friday,
which could bump up county-averaged accumulations into the
advisory range.

&&

.SHORT TERM /6 AM THIS MORNING THROUGH SUNDAY/...
Surface winds finally take on a northerly component on Friday,
particularly during the late morning and early afternoon. This is
expected to be the period when snow accumulations would be the
highest. Continuing the trend of the previous forecast shift, only
minor changes were made to snowfall accumulations. While there
will be an extended period of snowfall, there is no period with
especially high snowfall expected. Although accumulations across
northern portions of Mercer, Venango, and Forest counties could
reach advisory levels of three inches per 12 hours on Friday, do
not think that county averages will be high enough to justify any
advisories. Perhaps the one exception might be in Forest county,
with the 18Z RAP suggesting that a dominant band may develop to
the east and move into the county by 15Z, a forecast that is also
suggested by the 12Z GFS. This will bear watching by future
shifts. With the arrival of today`s trough, an extended period of
below normal temperatures has begun, with temperatures about ten
degrees below normal.


As winds begin to develop a southerly component once again Friday
night, snowfall accumulations should begin to diminish. As high
pressure builds in from the southwest Saturday, coverage of snow
showers should really decrease, with any minor accumulations limited
to locations north of Interstate 80. The break in precipitation will
be short lived as more precipitation will lift across the region
Saturday night into Sunday. This is expected to bring snow to all
locations, although models are still differing in how far south
precipitation will extend. So far it appears that snowfall totals
would be highest in the north, with minimal snowfall accumulations
to the south where rain may mix in. Below normal temperatures
will continue through this period.

&&

.LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/...
12Z GFS/ECMWF are in relatively good agreement that a warm front
will lift across the region Sunday night into Monday, and until
the entire region is in the warm sector, a period of freezing rain
could be possible before snow changes over to rain. Did not have
enough confidence in this to include freezing rain in the forecast
at this time. The surge of warm air should bring temperatures back
towards normal on Monday. Model agreement drops after the cold
front moves through Monday night, and while models both show high
pressure developing in the Plains and a storm system moving up the
East Coast, the differences in where those systems track result in
little agreement on precipitation, and have stayed close to the
SuperBlend with chance pops through much of the rest of the
forecast. After Monday`s near normal temperatures, temperatures
will drop back below normal, with another reinforcing shot of cold
air likely to drop many locations into the single digits Wednesday
night and keep some locations in the teens on Thursday.

&&

.AVIATION /06Z FRIDAY THROUGH TUESDAY/...
Expect that ceilings will be MVFR through most of the next 24
hours over the region, but periods of VFR, especially at the start
of the TAF period, will remain possible. Snow showers will
continue as well, with mainly VFR to MVFR visibilities overnight.
Expect coverage and intensity to pick up a bit after 12Z, with
occasional IFR visibilities becoming more likely along/north of
I-80 and along the ridges. Cannot rule out a brief dip to IFR
elsewhere as well. Wind gusts between 15 and 25 knots out of the
west will continue through tomorrow afternoon, with some
diminishment tomorrow evening.

.OUTLOOK...
Restrictions are likely through early Saturday under upper
troughing, and again Sunday and Monday with crossing low pressure.

&&

.PBZ WATCHES/WARNINGS/ADVISORIES...
MD...None.
OH...None.
PA...None.
WV...None.

&&

$$



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