Area Forecast Discussion
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FXUS61 KPBZ 191425

Area Forecast Discussion
National Weather Service Pittsburgh PA
1025 AM EDT Sat Oct 19 2019

Sunshine and warmer weather are in store today. This will make for
great viewing of the Fall foliage peak that is ongoing. Nestor will
race up the east coast Saturday night. This brings a glancing blow of
rain to the Laurel mountains south into northern West Virginia.
Warmer weather is forecast Sunday and Monday. Daytime highs Monday
will be in the 70s for a good chunk of the area, which will be the
warmest day of the entire forecast.


The Frost Advisory was allowed to expire on time at 10 AM, as the
shallow surface inversion is breaking and allowing temperatures to
rise. Abundant sunshine can be expected this afternoon behind
departing high pressure, with a few high clouds at most until closer
to evening. With warmer 850 mb temperatures as compared to yesterday,
temperatures will rise some 5 to 10 degrees above the highs

The remnant low of Nestor will lift northeastward across the
Carolinas tonight, spreading precipitation into areas southeast of
Pittsburgh after the late evening hours. Model QPF is in better
agreement in previous days, as the NAM aligns better with models like
the GFS and ECMWF in keeping deformation precipitation further to the
southeast. An increase in clouds will be seen in other regions, and
these plus ongoing warm advection will keep minimum temperatures
above normal, mostly in the mid and upper 40s.


Remnants of Nestor will be vacating the eastern zones by midday, so
will keep pops along and east of a DuBois to Morgantown line.
Additional rainfall will be less than two tenths of an inch. Moisture
in the boundary layer does not leave as quick as the precipitation
does. In fact, BUFR soundings for 2G4 and PIE support mostly cloudy
to cloudy conditions the balance of the day. A few of the 00Z NCEP
suite hint at a plume of moisture between H8-H7 Sunday afternoon over
eastern Ohio. Condensation pressure deficits between 300K- 310K run
around 125mbs, which supports maintaining an optimistic sky forecast
percentage in the 20 percentile range. The combination of building
mid-level heights into the lower 570s and H8 temps around 8C-10C
sunshine correspond to daytime highs well into the 60s save for the
higher terrain.

By Monday morning, an amplifying trough will shift east across the
CONUS on Monday. The surface reflection will be that of an
intensifying low quickly ejecting northeastward into the Upper
Midwest with a cold front extending southward through the Mississippi

Strong southerly flow and resultant warm air advection will make for
a rather warm Oct-21 across the region. Despite clouds increasing
through the day, the temperature should still approach or exceed 70
degrees for most locations. Given the cooler weather to follow, this
may very well be the last (or one of the last) 70 degree days for the
Pittsburgh metro this calendar year.

By Monday evening, the cold front and attendant rainband will extend
across the mid-Ohio Valley with the PBZ CWA in the warm sector of
the mid-latitude cyclone. Model forecast soundings depict only a
marginally favorable thermodynamic environment for tstorms, so have
opted out of mentioning in gridded forecast package. The front will
slowly push through overnight, reaching eastern Ohio around sunset
Monday, and then Pittsburgh and elsewhere later in the night.

Model consensus suggests somewhere in the vicinity of a half inch of
rainfall is most likely, though with a high upside given ample
moisture (2-3 Std Dev PWAT) and strong frontogenetical forcing.
Expect a belt or two receiving upwards of an inch, probably somewhere
south of the I-70/76 corridor.

Dry air and CAA behind the cold front will quickly shunt all the
precipitation to the east by around noon Tuesday or shortly
thereafter. Blended model guidance does suggest a few showers south
of the Erie lakeshore southward to Venango/Forest Counties, but an
unfavorable wind direction will result in little in the way of lake-
moisture for these showers. Given this, have gone below guidance late
Tuesday for these areas.


The trough responsible for Tuesday`s weather will depart by
Wednesday, placing the region underneath a building ridge in the low
/mid-levels and beneath quasi-zonal flow aloft on the south side of a
broad low centered over Ontario and the Hudson Bay.

Thursday will feature slightly warmer weather as the pattern
progresses, with the CWA now in southwest flow aloft and on the west
of the the surface ridge as it slides in the Atlantic.

From there, model solutions differ quite significantly. A strong
northern-hemisphere blocking pattern becomes established with the
Greenland High. GFS and ECM offer different solutions with regard to
the upstream wave progression with respect to the Greenland Block.
The progression will ultimately impact our sensible weather. Longwave
troughing will deepen across the central CONUS. The uncertainty lies
whether on the system will be more progressive as the ECM suggests,
or become a closed low as advertised in the GFS solution. The former
(ECMWF) would result in a cold front and rainfall for the area on
Friday, whereas the latter (GFS) remains mostly dry until Saturday
night. Have kept POPs limited to 20-30% during this timeframe until
models converge.

For temperature, both solutions offer near-climatological values w/
no strong symbol for anything too anomalous.


Fog has mostly burned off, leaving VFR conditions for the balance of
the daylight hours. Some increase in mid and upper clouds on the
outer fringes of the Nestor cloud shield can be expected tonight, but
any flight restrictions should remain off to the south and east of
TAF sites. Wind will be light from the southeast at less than 10

MVFR and IFR restrictions are likely with Monday night into Tuesday
when a cold front passes.




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