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NWS Area Weather Forecast Discussion
County Warning Area [CWA]: PBZ
Regional NWS Weather Office: Pittsburgh, PA

FXUS61 KPBZ 281220

Area Forecast Discussion
National Weather Service Pittsburgh PA
720 AM EST Sat Nov 28 2020

Dry and seasonable weather is expected this weekend under high
pressure. Strong low pressure will then bring rain on Monday,
followed by accumulating snow from Monday night through Tuesday,
along with much colder temperatures.


Recent satellite imagery and sfc obs suggests eroding cloud cover and
decreasing dewpoint values across east-central Ohio in shortwave
ridging behind a crossing thermal trough. Increasing subsidence area-
wide should impede remaining boundary layer moisture, supporting a
clearing sky and seasonable temperature through the period.

Dry and warmer conditions can be expected Sunday as ridging
amplifies in response to a deepening southern Plains low. Sunday will
be a sunny day, perhaps the last in quite a while, though some
higher clouds may eventually overspread the area by the latter half
of the day as the subtropical jet inches northward.


After a rather meteorologically-benign weekend, a low pressure
system is expected to bring a mix of rain and snow to the Upper Ohio
Valley and Allegheny Mountains.

Models continue to indicate the phasing of a northern stream
shortwave dropping out of the Upper Midwest and southern stream
system ejecting out of the ArkLaTex region. The resultant surface
cyclone will deepen and move northward along or just west of the
spine of Appalachian mountains. As the low approaches the Upper Ohio
Valley, precipitation associated with the warm front shield on the
north side of the comma low will overspread the area south to north
under highly diffluent flow aloft. At precipitation onset and
through the first half of Monday, precip-type will very likely be
rain for all locations across the forecast area as boundary layer
temperatures remain quite warm.

Much colder air will then cascade southward and wrap around the low,
eventually resulting in a transition from rain to snow across
eastern Ohio and perhaps NW PA by sunset or soon thereafter, followed
by a transition across the remainder of the area through the
overnight hours. The deformation band in the trowal sector of the low
may lead to a brief period of heavy snow on the northwest side of
the low, which could end up as far south as somewhere from perhaps
New Philadelphia OH to Mercer PA, but confidence in longevity of
band over one particular location, position, and transition time all
remain low.

Snow showers will likely continue through much of the day Tuesday
and into Tuesday on the backside of the departing low thanks to wrap
around moisture and divergent flow in conjunction with some lake
enhancement. However, it doesn`t appear there`ll be any strong
mesoscale features resulting in abundantly high snow rates on

Regarding snow accumulations, models have come in to much closer
alignment with the lows position and progression, which yields a
higher confidence snow forecast... though the heavy snow possibility
mentioned above is still questionable. Ensemble spread has been
greatly reduced with the mean snow total accumulation for much of the
Upper Ohio Valley, including Pittsburgh, somewhere in the 1 to 3
inch range... which definitely seems like a realistic solution. As
mentioned above, New Philly to Mercer may receive a bit more if
they`re close enough to a mesoscale band, along with the higher
elevations in the Allegheny Mountains which will receive an upslope
component towards the end of the event. These locations may very well
receive snow in the 2 to 5 inch range once the event wraps on

As for temperatures, highs will generally be in the 40s to around 50
on Monday afternoon followed by a sharp drop to the upper 20s and
low 30s by Tuesday morning once cold air ushers in. Tuesday highs
will likely occur at midnight, with afternoon temperatures remaining
steady in the upper 20s and low 30s.


Cold northwesterly flow in the wake of the departing system will
support continued chance for intermittent snow showers through
Wednesday. Thursday will be dry before another set of northern and
southern stream troughs transition across the region. The southern
stream cyclogenesis will be a bit more potent and may result in a
little rain across the southern forecast area (/northern WV) on


Some lingering low level cloud will continue to linger across the
area in northwest flow creating some uplift. The the lower levels
will begin to dry out with the approach of high pressure and drier
air. Thus, will expect the MVFR and IFR cigs to dissipate. Will
expect VFR conditions through the rest of the TAF period with west to
northwest winds becoming light.

Restrictions and variable pcpn type are likely through mid week as
strong low pressure slowly traverses the region.





Forecast Discussion from: NOAA-NWS Script developed by: El Dorado Weather