Area Forecast Discussion
Issued by NWS Pittsburgh, PA

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FXUS61 KPBZ 272349

Area Forecast Discussion
National Weather Service Pittsburgh PA
649 PM EST Sat Feb 27 2021

After a dry evening, rainfall chances return as low pressure and a
warm front cross late tonight and Sunday. South of Pittsburgh, areas
of heavy rainfall are expected. Mostly drier and cooler weather
returns early next week.


Weak surface high pressure will remain in effect through the rest of
this evening and into the overnight. Some breaks in the cloud cover
this evening has led to some warming allow temps to be a few degrees
warmer. Cloud cover will then begin to fill in across the area later
tonight as the next shortwave moves into the region.

Previous Discussion...There has not been much change to the thinking
regarding the expected heavy rainfall event south of Pittsburgh late
tonight into Sunday night. The next shortwave in embedded southwest
flow aloft will ride northward late tonight and cross by late Sunday,
with an associated warm front setting up over the middle Ohio Valley
Sunday morning. After a dry period this evening, categorical PoPs
are still appropriate CWA-wide. Northward progress of this front may
be hindered initially by high pressure over the northeast CONUS,
setting up at least modest cold air damming on the eastern
Appalachian slopes. This could increase the front`s residence time to
the south and east of Pittsburgh.

Forcing for ascent will be maximized in that area as well. The right
entrance region of an upper jet will provide upper divergence, while
low level convergence/frontogenetic forcing will be strong in the
area of the warm front. Moisture will be abundant, with precipitable
water values approaching 1.25 inches, which is near the top end of
climatology. All of these factors decrease in intensity further north
and west, but the majority of the region will experience a soaking
rain. Have elected to expand the Flood Watch into Fayette County
given the presence of the stronger moisture/forcing here, as well as
still-present snow on the ridgetops. A total of 1.5 to 2.5 inches of
rain still looks likely in the watch area through Sunday night.
Combined with snowmelt, this rain is likely to create both areal
flooding and river flooding. Rainfall amounts will steadily decrease
to the north and west of the watch.

Rain coverage/intensity may start to drop off Sunday afternoon in
southeast Ohio as drier air works into the mid-levels, leading to a
decrease in PoPs. However, steadier rain is likely to continue in
the southeast CWA where low-level convergence and deeper moisture
remain. Despite the rain, temperatures will run well above
climatology given the strong warm advection.


Rainfall will gradually end Sunday night as the shortwave departs,
and the system`s cold front makes a passage. The last of rain will
exit the southeastern CWA by Monday. Some sunshine will return to
most areas as surface ridging increases from Mississippi Valley high
pressure. Another shortwave crossing the northern/eastern Great
Lakes may create some light snow to the north of I-80 Monday
afternoon and evening, with minimal accumulation. Dry weather will
then return by Tuesday morning. Temperatures will drop off to
seasonal levels on Monday, with a chilly night in the teens forecast
the following night as the surface high arrives.


Dry weather will continue under high pressure on Tuesday, although
temperatures will remain a bit below climatology with 850mb
temperatures remaining below -10C for much of the area.  Latest
model runs show a more southerly track with the Tuesday
night/Wednesday shortwave, and will be reducing PoPs accordingly.
Temperatures will recover back to above climatology by Wednesday as
mid-level heights rise.

Thereafter, a modest increase in moisture from the south, plus a
shortwave tracking across the central/lower Mississippi Valley, may
provide precipitation chances towards the end of the extended
period. Confidence remains low with details this far out, and so
maintained slight chance PoPs for now. Temperatures will continue to
run just above the calculated normals.


VFR is expected to continue this evening before quick deterioration
to IFR with rain Sunday morning. Restrictions should continue through
the end of the TAF period, with some easement in reduced vsby Sunday
afternoon as rainfall intensity lightens.

Restrictions with rain potential will continue into Monday with
crossing low pressure before high pressure and quiet weather return.


1.5 to 2.5 inches of rain appears likely from late tonight through
Sunday night in the Flood Watch area. Combined with snowmelt, this is
likely to create flooding on some area small creeks and streams.

River Flood Warnings have also been posted at several points along
the Monongahela and Cheat Rivers. The Cheat in particular will have
to be watched closely, as snowmelt and rainfall will be highest in
that basin. Flooding in the moderate category is currently forecast
at Rowlesburg. Minor flooding is also expected at Parsons on the
same river, and minor to moderate flooding is foreseen at Point
Marion, Charleroi, and Elizabeth on the Monongahela.


PA...Flood Watch from 4 AM EST Sunday through late Sunday night for
WV...Flood Watch from 4 AM EST Sunday through late Sunday night for


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