Area Forecast Discussion
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FXUS61 KPBZ 230521 AAC

Area Forecast Discussion...UPDATED
National Weather Service Pittsburgh PA
121 AM EDT Mon Oct 23 2017

A cold front will return rain to the area through tonight. Low
pressure will maintain shower chances and cool temperatures
through mid week.


No major changes to the overnight period.

Complex system will bringing rain and wind to the area today.
Deepening 500mb low will move from the Lower Mississippi valley
north-northeastward toward the Ohio Valley by this afternoon.
Strong shortwave energy will rotate around the upper low as it
moves toward the region. At the surface, low pressure will
develop on the northern flank of the cutoff system this
afternoon, and its accompanying surface front, will stretch from
the Upper Midwest low pressure, southward, all the way into the
Gulf of Mexico. As the entire system deepens, wind fields
throughout the atmosphere will strengthen, further enhancing the
system. Strong winds aloft will pull moisture northward from
the Gulf, while low-level winds, on the eastern side of the
system, will tap into Atlantic moisture. This process will
enhance rainfall coverage and intensity ahead of the boundary as
it swings eastward. The main rain-shield will begin to
overspread my western counties early this afternoon, with full
coverage of the region expected by early evening. Scattered
showers could develop ahead of the main area of rain under
height falls and low-level moisture convergence, but this should
remain light. Rain could become heavy at times, directly ahead
the surface front, as the increasing large scale ascension and
low-level convergence interact with the substantial atmospheric
moisture. Ballpark model timing would place the risk for
heavier rain over Ohio/Northern WV late this afternoon and

Tightening surface pressure gradient this afternoon, and
lowering mixing heights, will increase surface winds today and
promote stronger gusts, with the highest over the eastern
ridges. Models still not in real good agreement on gust strength
in the lower elevations, however occasional gusts to 40mph are
possible in the ridges.

Temperatures will remain warm today, with readings 5 to 10
degrees above normal.


500mb low will interact with strong northern stream energy
diving southward from the northern Plains into the Midwest
tonight. This phasing will further deepen the surface low,
which by this time, will be moving rapidly northward over the
Western Great Lakes. The upper level phasing and strong wind
field aloft will increase the forward speed of the surface front.
This will mean the threat for heavy rain continues just ahead
of the boundary, but it will not last long as it streaks east-
northeastward. The heaviest rain should exit the region shortly
before midnight. By late tonight the northern energy will take
over, as it absorbs what is left of the southern low. As this
process ensues, a large dry slot will develop ahead of the main
upper low, decreasing rainfall coverage into Tuesday. The area
will remain in the dry slot through Tuesday morning, until a
second surface front/shortwave trough rolls through Tuesday
afternoon. The risk for scattered showers will return and this
will be the initial push of the much colder air.

A second dry slot develops Tuesday night, so would expect most
of the region to remain dry. However, the strong cold air
advection will be under way.

The main trough axis looks to slowly cross the region on
Wednesday, continuing the cold air advection and returning the
risk for scattered showers. High temperatures on Wednesday will
be 10 to 15 degrees below normal.


The chance for showers will come to an end late Wednesday night
as the upper low moves east. Thursday and Friday should remain
cool and dry. While the ECMWF and GFS have general agreement of
low pressure dragging a cold front to the area for the weekend,
the models have shown little consistency in the speed of the
front and when any precipitation would arrive. Have stuck close
to the Superblend for this portion of the forecast.


VFR conditions will continue through most of the morning as
high pressure erodes in advance of Midwestern low pressure.
Expect condition deterioration to low-end MVFR through the
afternoon as that trough advances and spreads rain over the

Periodic restrictions will continue into early Thursday with
the region under upper troughing.




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