Area Forecast Discussion
Issued by NWS Pittsburgh, PA

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FXUS61 KPBZ 081731

Area Forecast Discussion
National Weather Service Pittsburgh PA
131 PM EDT Sat May 8 2021

After a quiet evening, widespread rain will begin to arrive late
tonight and continue across the region into Sunday evening. High
pressure will provide a mostly dry start to the work week, although
temperatures will remain below normal.


Northwest flow and a departing shortwave are responsible for the
continued rain showers across the region during the early afternoon
hours. Steep low level lapse rates are also aiding some gusty wind,
and even just enough instability for small hail in a few cases with
the cold air aloft. These showers will end over the next few hours as
surface ridging starts to build in. Transitory high pressure will
provide a brief dry break during the afternoon and into the evening.

After the quiet evening, moisture advection ramps up, and clouds
will begin to increase from the southwest especially after midnight.
Will leave the current frost advisory as is, thinking clouds in the
northern counties may hold off just long enough for some dew/frost
formation before the thicker cloud cover arrives toward sunrise.
Precipitation chances will increase after midnight ahead of a warm
front rising north in the Middle Ohio Valley, especially to the
south and west of Pittsburgh.  Some snow may mix in initially in the
higher elevations, with virtually no appreciable accumulation.
Temperatures will be well below normal once again, with mid 30s in
the Frost Advisory area/higher elevations.


A period of moderate to heavy rainfall is still expected for Sunday
and Sunday night.  Models continue to track the surface low a bit
further north, generally in the vicinity of the Middle Ohio Valley
and the Mason-Dixon Line.  The heaviest rainfall totals still appear
likely across the central/northern portions of the CWA.  Here,
precipitable water values of 1 to 1.2 inches will be transported on
the heels of a strong southwest 850mb jet, into a region of enhanced
frontogenesis and right entrance region upper jet dynamics. Around
1.5 inches of rainfall is possible in this region in a 24 hour
period, with slightly lesser totals on either side of this axis.
Think that the rainfall will be spread out enough to avoid all but
minor high water issues, and will continue to mention this in the
HWO.  Model soundings continue to indicate quite stable
conditions in the lower levels. This will not only preclude
much in the way of thunderstorm chances and the resulting QPF
bullseyes, but it will also prevent the mixing down of the strong
low-level jet and any concerning surface wind gusts.

The low will depart by Monday morning, with only a few lingering
morning showers to the southeast of Pittsburgh.  Increasing surface
ridging will then provide dry weather through Monday night, with
continued below-normal temperature.  Some cloud cover may linger
through Monday night underneath a subsidence inversion.  A
frost/freeze concern may reappear if these clouds remain subdued in


An upper low swinging across far southern Canada will drag a
shortwave trough across the region Tuesday afternoon and evening.
Only a few light showers are expected across the north from this.
Another round of frost/freeze concerns is possible on Tuesday night
as an approaching mid-level ridge helps clear the sky. That ridge
will keep mostly dry weather in the forecast through Wednesday night,
with continued below-normal temperature.

Some model strength/timing differences start to emerge for Thursday
and Friday, with the ECMWF keeping a weaker and more
progressive flow pattern over the Great Lakes/upper Ohio Valley as
opposed to the GFS. For now, will stick with ensembles/model blends
which indicate some rain chances returning to the region, with
perhaps a dry Saturday to end the extended period.  Temperatures
will finally approach climatology by Saturday.


Mainly VFR/patchy MVFR cu/stratocu cigs are expected through sunset
with a crossing upper trough and cold air aloft. Sct shra should
diminish through the aftn as the trough exits, and sfc high pressure
briefly builds in. Mid lvl clouds should increase tonight ahead of
approaching low pressure. MVFR/patchy IFR restrictions in rain are
expected by Sun morning as the low tracks across the Upper OH Vly

A sfc pressure gradient and mixing should result in WNW wind gusts to
around 20 kt this aftn, before diminishing this evening.

Restrictions and rain are expected through Sun night with crossing
low pressure.


PA...Frost Advisory from 1 AM to 8 AM EDT Sunday for PAZ007>009-013>016-


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