Area Forecast Discussion
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FXUS61 KPBZ 210606

Area Forecast Discussion
National Weather Service Pittsburgh PA
106 AM EST Sat Jan 21 2017

Mild weather will continue through the weekend. Widespread rain is
expected to move back into the region Sunday afternoon.


Issuing a dense fog advisory for northern counties. Many ob sites
are reporting one-quarter mile or less. Will start immediately and
continue until 13z.

No major changes to the overnight period. Just some minor
adjustments to cloud cover and temperatures have been updated with
a blend of hires guidance.

Ridging aloft will keep the area dry today. However, plenty of
moisture will be trapped below the ridge, so clouds will hang
around. Temperatures will be well above normal.


Operational models are coming into better agreement on the overall
pattern during the short term. Upper level energy will cutoff over
the Texas panhandle this evening and move eastward tonight,
reaching TN/AL by Sunday evening. A powerful jet will swing
around the 500mb low and drive northward toward the Mid-Atlantic
region. This will pump copious amounts of moisture northward
through the Mid-Atlantic and into the Ohio Valley on
Sunday/Sunday night. In addition to the moisture, waves of energy,
revolving around the upper low, will also move northward Sunday
afternoon. At the surface, low pressure will rapidly develop
beneath the upper low tonight and move quickly eastward on Sunday
with the strong upper level support. Seeing some differences
between the NAM/GFS on the surface low placement Sunday afternoon,
so will lean toward the GFS, as it is showing better agreement
with both the GEFS and EPS.

Showers will quickly overspread the area Sunday afternoon and
continue through Monday. The upper level low will become
negatively tilted on Monday and slow down, as it battles the
responding ridge that will stretch from the Atlantic Ocean
northward over Northern New England. With the placement of the
upper low and the strong jet on its eastern flank, the heaviest
rain would likely move through our region late Sunday night and
Monday morning. After this time, the jet axis will take aim at
Eastern Pennsylvania, shifting the highest qpf into the areas.

With the absence of arctic air, all of the precipitation on
Monday will remain in the liquid form.

Temperatures Sunday and Monday will again be above normal, but
Monday will be noticeably cooler.


On Monday night, operational models begin to move away from the
ensemble data, and even the ensemble data is not agreeing on what
the lows track will be on Tuesday. Still expect showers on
Tuesday, but depending on what the surface low actually does, snow
flakes may mix as colder air wraps around the exiting system.
Additionally, the ending of the precipitation is not set in stone
due to the aforementioned model differences.

Warmer air will quickly move back into the area on Wednesday as
southwest flow will ensue ahead of the next system, which will
move from the Upper Midwest to the Great Lakes late Tuesday night
and Wednesday. This midweek system will bring scattered showers
back into the area. By the end of the long term, a return to more
normal January air is expected with snow showers possible.


With plentiful low level moisture and a surface-based inversion
that will linger through the night, fog will be an issue at most
terminals, particularly across the north where LIFR or worse
visibilities will linger through the night. More variable
conditions are expected across the south with just a bit of mixing
and a slightly drier airmass, although IFR/LIFR is certainly
possible at any terminal. Fog will thin and lift by midmorning
with VFR conditions, although IFR ceilings may linger north of
PIT through midday.  Winds will remain light.

More restrictions are likely Saturday night into Monday with slow
moving low pressure.


PA...Dense Fog Advisory until 8 AM EST this morning FOR PAZ007>009-


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