Area Forecast Discussion
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FXUS61 KPBZ 091054
Area Forecast Discussion
National Weather Service Pittsburgh PA
554 AM EST Fri Dec 9 2016
Occasional snow showers will continue through tonight, especially
north of Pittsburgh, and will taper off on Saturday. Accumulating
snow is expected for much of the region on Sunday.
.NEAR TERM /THROUGH TONIGHT/...
550 AM...Main broken lake effect band has sunk a bit further south
and weakened somewhat. Got reports of 1-1.5 inches in Mercer
County in the band. Little indication of any totals higher than
this at this time. Did increase PoPs a bit for the band in
Lawrence/Butler/Armstrong Counties and added around a half inch of
accumulation. Little change elsewhere for now.
Core of the coldest 850mb temperatures now lies across the
southern CWA and will continue to move south. Thus, although NW
flow will continue at this level, temperature advection will be
near neutral through the day. Low level flow becomes a bit better
aligned in a WNW/NW direction later this morning into the
afternoon, and still expect that this will be the period with the
best overall accumulations. Made some slight upward adjustments to
amounts in some locations, particularly along the northern CWA
border and along the ridges. Still not quite enough for headlines
at this time due to snowfall duration, but cannot rule out an
issuance if a persistent band sets up. Forest County still has the
best chance of this, but confidence was not high enough for an
issuance at this time.
Coverage/intensity of snow showers will slowly wane after 00Z as
inversion heights lower and winds start to settle a bit more
towards the west in the low levels. An additional 1-1.5 inches is
possible north of I-80, with possibly up to an inch along the
ridges, and less elsewhere. Temperatures will continue to run 5-10
degrees below normal.
.SHORT TERM /SATURDAY THROUGH MONDAY/...
By daybreak Saturday, only the extreme northern edge of the forecast
area will remain near the downlake moisture plume. Will linger
chance PoPs in this area for now, but little additional accumulation
is expected. Surface high pressure will bring dry weather through
late Saturday evening, but the next system will already be
approaching from the west.
A complex system will move into the region by Sunday, stretching
into the new work week. Modest isentropic lift along a weak warm
front will lead to the onset of snow by daybreak Sunday. Models
differ slightly with the placement of this initial band, but the
mean of guidance centers the highest PoPs over the northern and
western counties. This boundary will be the focus for light to
moderate snow through Sunday afternoon, while a system organizes in
An amplifying upper-level trough will push the deepening surface low
through the southern Great Lakes Sunday night into Monday. As the
warm front lifts north, we end up in the warm sector, with strong
warm air advection. A non-diurnal temperature trend will bring a
change from snow to rain Monday morning, at least for the southern
half of the forecast area. Guidance has been inconsistent with the
track of the low, subsequent warm air advection and precipitation
types. At this time, chose to be a little general with a rain/snow
mix Monday morning, until finer details can be hashed out.
Regardless, accumulating snow is likely from Sunday afternoon into
Monday, primarily north of Pittsburgh. There is also a possibility
of pockets of freezing rain in the favorable mountain locations
Monday morning, where easterly flow dams up the colder air. Will
carry a mention in the HWO for this system.
.LONG TERM /MONDAY NIGHT THROUGH THURSDAY/...
Any lingering shower activity behind the cold front Monday night
should transition back to snow with falling temperatures.
Transient high pressure will briefly lead to drier period into
Tuesday. Largely zonal flow will then bring several disturbances
through the latter part of next week. With significant guidance
differences existing through this time, SuperBlend was relied on
heavily. After near normal temperatures Monday, temperatures will
drop back below normal through the end of next week.
.AVIATION /12Z FRIDAY THROUGH TUESDAY/...
Ceilings/visibility will likely flop between MVFR and VFR for
much of the area today depending on location and intensity of snow
showers. Brief IFR will be possible at any terminal but such
restrictions will be difficult to time. Best chances of IFR
visibilities will lie along/north of I-80 and along the higher
ridges. By the evening hours, restrictions will become less likely
as winds start to take more of a westerly component and
coverage/intensity of snow showers lessens. VFR ceilings will
become more prevalent as well. Wind gusts of 15-25 knots will
continue through the day, with winds decreasing to 10 knots or
Restrictions are likely through early Saturday under upper
troughing, and again Sunday and Monday with crossing low pressure.