Area Forecast Discussion
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FXUS61 KPBZ 122306

Area Forecast Discussion
National Weather Service Pittsburgh PA
606 PM EST Mon Nov 12 2018

A mix of rain and snow is expected tonight and Tuesday with the
approach and passage of a cold front. Dry but cold conditions
are expected Wednesday with building high pressure.



Minimal change needed this evening as the ongoing forecast
aligns well with latest observational trends.
Previous discussion follows..

Digging upper trough over the central CONUS will
lift a low pressure system northeastward tonight. While the low
pressure system itself will remain well to our east, we will
receive some precipitation along the northwest flank as a result
of interaction with a cold front, analyzed just west of our
region currently, and a shortwave embedded in the upper flow
over the Great Lakes. Some moisture is already spreading into
our southern zones though much of this is most likely virga or
light rain/snow given dewpoint depressions.

As a result of the aforementioned upper pattern, a mix of rain
and snow is expected, especially as you head north and west
into OH and NW PA given model soundings and wet-bulb processes.
Accumulation will be limited given boundary layer temperatures
at onset, with rain anticipated for a bulk of the period over
the south until cold advection resumes Tue morning. Overall,
with most of the lower half of the column below efficient
snowfall growth and expected air temperatures, kept snow ratios
very low, with maybe an inch or two possible in our northernmost
zones. Low temperatures will remain near seasonal averages.


The surface low will rapidly head toward the NE coast on
Tuesday. Strong cold advection is expected, though the period
for efficient snow fall is rather short as dry air advects
overhead and moisture below the inversion has difficulty tapping
into the dendritic growth zone. That and given forecast wind
direction aloft, would think the focus for snow showers
initially would be over the I-80 corridor with the development
of Lake Bands. Better conditions for upslope snow showers over
the ridges would hold off until later in the afternoon.

By Tuesday night, strong subsidence will really limit any
further snow production and accumulation. Have minimal amounts
in the north and ridge zones through Wednesday morning.

High pressure will build overhead for Wednesday with cloud cover
diminishing. That being said, temperatures both Tuesday and
Wednesday will remain 10-15 degrees below seasonal normals.


Next low pressure system is still progged to approach Thursday
although there remain some timing issues given strength of the
upper low. Maintained likely PoPs but adjusted timing a bit
slower given latest ecmwf and nam guidance. That being said,
there still remains some concern for freezing rain/mixed precip
at onset on Thursday, though this may be less of a concern if
the models continue to slow the system down. Have opted to add
the freezing rain mention, though confidence is still low given
timing concerns.

After this systems departure, the broad upper will be reinforced
maintaining the chance for showers and below average
temperatures through the weekend.


Expect condition deterioration with the approach of low
pressure, with widespread rain and snow, and eventual low
MVFR/IFR tonight. As precipitation moves in from southeast to
northwest, expect showers could begin at MGW as early as sunset
and take as long as midnight to reach FKL and ZZV.

Widespread restrictions are likely to continue Tuesday as cold
advection ensues in the wake of the Monday night low pressure
system. After VFR conditions on Wednesday, another system will
bring widespread restrictions Thursday into Friday.




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