Library, Pennsylvania Weather Forecast Discussion

729
FXUS61 KPBZ 181134
AFDPBZ
Area Forecast Discussion
National Weather Service Pittsburgh PA
734 AM EDT Thu Sep 18 2025
.SYNOPSIS...
High pressure will maintain warm and mostly-dry weather into
the weekend. Rain chances return to the forecast next week,
though the chance for widespread wetting rain remains low.
&&
.NEAR TERM /THROUGH TONIGHT/...
KEY MESSAGES:
- Areas of fog possible early this morning, especially in
  valleys
- Above-normal temperatures continue
---------------------------------------------------------------
Eastern-CONUS low pressure weakens into an open wave as it
tracks into the northeastern CONUS today. Most of its
associated cloud cover has departed, and the combination of
clear sky, light wind, and lingering surface moisture could
support some valley fog early this morning. The HREF continues
to support this, showing a moderate signal (40-50% probability)
of below 0.5 mi visibility for some locations north and east of
Pittsburgh, especially in a corridor from Connellsville to
Dubois PA, and from Franklin PA to Youngstown OH.
Warm temperatures are forecast across the board this afternoon
with plenty of sun and building heights. Expect widespread
highs roughly 10 degrees above normal (lower and middle 80s).
&&
.SHORT TERM /FRIDAY THROUGH FRIDAY NIGHT/...
KEY MESSAGES:
- Dry weather continues to end the work week
- A weak front brings cooler temperatures north of US-422, while
  areas farther south remain around 10 degrees above normal
--------------------------------------------------------------
As the nern CONUS trough continues to depart to the east, a
blocking ridge centered over the lower Mississippi Valley and
western Great Lakes makes slow eastward progress with time and
sets up shop over the Middle and Upper Ohio Valley by Friday. At
the surface, a weak boundary will likely settle into our region
before stalling out. A few model solutions actually attempt to spit
out some light QPF with this front Friday/Friday night, but that
appears unlikely given the magnitude of dry air currently in
place that would need to be overcome (via moisture advection or
sub-cloud evaporation) as well as the lack of sufficient
support/forcing with increasing heights. The most recent NBM
run carries sub-10 PoPs Friday and Friday night, which sounds
far more reasonable. Thus, the forecast continues the extended
run of dry weather through Friday night.
Highs will be a little more subdued north of US-422 on Friday
behind the front, backing off to the upper 70s/around 80, while
highs to the south remain around 10 degrees above normal.
Similar trends will be seen with overnight lows, although they
will be a bit closer to climatology.
&&
.LONG TERM /SATURDAY THROUGH WEDNESDAY/...
KEY MESSAGES:
- Still mostly dry and warmer than normal through the weekend
- Slight uptick in rain chances next week
- Temperatures remain above normal Monday through Wednesday,
  albeit with a slight downward trend
------------------------------------------------------------------
Despite the frontal boundary wavering in our region, a largely
dry pattern is forecast for Saturday as the upper ridge axis
crosses, with high temperatures similar to Friday. However,
there is a bit better potential for a light shower or two in the
ridges southeast of Pittsburgh, with better indications of
moisture and modest low-level convergence. Still, chances of a
wetting rain from this activity remain under 15 percent.
Ensembles/cluster analysis continue to show a slower trend with
the progress of the next upstream trough, with the axis
progressing from the Upper Mississippi Valley on Sunday to just
the Western/Central Great Lakes by Tuesday. Some solutions even
suggest the development of a cutoff upper low somewhere over the
eastern Plains. This trend, in turn, results in just a slow
increase to minimal PoPs, with slight chance values northwest of
Pittsburgh Sunday night/Monday, before eventually overspreading
the area Tuesday/Wednesday. QPF expectations are not high. The
NBM shows a 40-60 percent chance of 0.10" or more during the
72-hour period ending at 12Z Thursday. With increasing rainfall
deficits, we will need healthier precipitation totals to put a
better dent in the developing drought.
Overall, above-normal temperatures continue to be the
expectation through the middle of next week. Still, with the
slowly falling heights and increasing cloud cover potential, a
modest downward trend is the most likely scenario. The 25th-75th
percentile spreads do increase through this period, indicating
increasing uncertainty in the ultimate values. This is
reasonable given the range of potential solutions regarding the
speed/positioning of the upstream trough.
&&
.AVIATION /12Z THURSDAY THROUGH MONDAY/...
VFR is favored through the TAF period as high pressure remains
in control. Morning valley fog, mostly prevalent at HLG, will
erode by 13Z as mixing ensues. Cloud cover will generally be
limited to fair weather cumulus for the bulk of the afternoon,
and these clouds will collapse with sunset. West-to- northwest
wind will stay near or less than 10 knots.
.OUTLOOK....
VFR is favored under the influence of high pressure with
localized morning river-valley fog through Sat. The exception
is increasing probabilities for a weak cold front sagging into
nwrn PA Fri morning that may lead to MVFR cigs (30-50% likelihood
at FKL/DUJ).
Approach of an upper-level trough may foster low-probability
rain/sprinkles Sun/Mon, favoring locations northwest of
Pittsburgh, but VFR is likely to persist.
&&
.PBZ WATCHES/WARNINGS/ADVISORIES...
PA...None.
OH...None.
WV...None.
&&
$$
SYNOPSIS...Cermak/Kramar/CL
NEAR TERM...Cermak/Kramar/CL
SHORT TERM...Cermak/CL
LONG TERM...Cermak/CL
AVIATION...Rackley/CL

NWS PBZ Office Area Forecast Discussion