Area Forecast Discussion
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FXUS61 KPBZ 211003

Area Forecast Discussion
National Weather Service Pittsburgh PA
503 AM EST Tue Feb 21 2017

A weak system will pass the region late today with a chance of
some showers, however warm conditions will continue through the


A fairly long fetch of elevated RH values in the layers
generally above 300 mb extends across the entire CWA already
very early this morning. This is well out in advance of a mid
and upper level system currently splitting off from the upper
flow in the Mississippi Valley. The vast majority of the
moisture and lift will remain with the cut off low that will
meander into the southeastern portions of the country. The
remnant upper level wave in the northern stream will take its
sweet time crossing the Great Lakes region on Tuesday, only to
edge as far eastward as our area by very late in the day.

Deep saturation with this system remains generally north of our
area. In addition, as the H5 wave shears off to the north
through Tuesday night, lift along the boundary as it shifts
through the CWA on Tuesday night is looking fairly paltry.
Beyond that, deep moisture is entirely lacking. That said, PoPs
were trended back below likely threshold for the vast majority
of the area with the boundary passage on Tuesday night. In fact,
some guidance (the new 00z NAM) is trending toward a basically
dry passage of the system.

Regardless of the chances of rain, somewhat translucent high
clouds will likely keep a lid on insolation driven upward
temperature mobility on Tuesday, however warm advection will
continue to do its thing. This warm advection combined with a
notable uptick in boundary layer mixing as compared to yesterday
should certainly result in a warmer Tuesday than Monday. Fries


Nearly zonal/flat ridging will support fast moving shortwaves
through the flow through Thursday. While most of the support for
any precipitation should remain well north of the region,
increasing moisture in w-sw flow may lead to widely scattered
showers until the more amplified low pressure system ejects
into the Plains and lifts a warm front across the upper Ohio
Valley. Generally kept chance PoPs through the period based on
the uncertainty in guidance and lack of deep moisture and lift.

With little modification in 850hpa temperatures, expect values
to remain 20+ degrees above seasonal averages. It still looks
like one our warmest days this week will be Friday, as most
ensemble guidance has over 70 degrees here at Pittsburgh. The
only thing that could hamper this would be cloud cover and any
shower coverage.


Models continue to slow the progression of the strong cold
front, with it`s current timing progged for early Saturday. Will
continue with likely PoPs for this boundary, with a chance for
thunder, though the overnight passage may be a bit of a limiting
factor. Temperatures should return to near normal values, with
snow showers as the system departs.

Very broad troughing is then expected through the end of the
forecast period, with another system progged for passage in the
deterministic guidance. Seasonal temperatures will continue
through the start of the work week.


VFR can be expected through much of Tuesday although extensive
high cloudiness will mar the sky. Sfc wind will veer to the south
by daybreak as sfc high pressure gives way to an advancing
trough. Some restrictions will start to edge in from the north
on Tuesday night as a weak system shifts through the Great
Lakes. High uncertainty exists on exactly how much shower
activity will remain as it gets to our region as well as the
degree to which ceilings and visibilities may fall as it passes.

Restrictions are likely with a Friday night/early Saturday cold




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