PBZ issues Area Forecast Discussion (AFD) at Oct 17, 5:18 PM EDT
301
FXUS61 KPBZ 172118
AFDPBZ
Area Forecast Discussion
National Weather Service Pittsburgh PA
518 PM EDT Fri Oct 17 2025
.SYNOPSIS...
Dry weather is expected for most of the area through Saturday,
though a weak warm front will bring a chance for light rain or
drizzle north of Pittsburgh late tonight. A strong cold front
will bring showers, thunderstorms, and gusty winds on Sunday.
&&
.NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
KEY MESSAGES:
- A few showers/sprinkles late tonight, mainly north of
Pittsburgh
---------------------------------------------------------------
As mentioned earlier today, there are some weak returns on
radar to the north of the area, which may allot a brief
sprinkle overnight as ascent aloft moves overhead. For the most
part, dry air will limit most people seeing any rainfall. The
onset of warm advection aloft and occasional clouds will
preclude any chances of frost or freeze tonight. The forecast
remains on track.
.. Previous Discussion ..
Clouds will increase this evening into tonight from northwest
to southeast as mid and upper level moisture rides around the
northern periphery of the ridge. There is a small chance that a
few light showers or sprinkles fall out of these late tonight
into early Saturday morning, mainly along/north of I-80. A
significant dry layer is still expected to be in place below
700mb, leading to sub-cloud evaporation that will limit any
rainfall accumulation to a couple hundredths of an inch at best.
Farther south, the near- surface environment is expected to
remain too dry for anything more than a passing sprinkle.
&&
.SHORT TERM /6 AM SATURDAY MORNING THROUGH SUNDAY NIGHT/...
KEY MESSAGES:
- Well above normal temperatures this weekend
- A cold front passage Sunday offers higher rain chances and
windy conditions
- A few storms Sunday afternoon could be strong/severe, with
damaging wind gusts and possibly a brief tornado being the
main threats
----------------------------------------------------------------
The upper ridge that has provided us with dry weather in recent
days finally pushes off to our east on Saturday as a trough
deepens upstream over the central CONUS. This shift establishes
southwesterly deep-layer flow across the Ohio Valley, resulting
in gradual moisture return and warm advection which will help
temperatures on Saturday climb well above seasonal levels (in
some cases as much as 15+ degrees above normal).
Meanwhile, a rather potent shortwave trough ejects from the
southern Rockies, traversing the southern Plains (OK/TX) before
phasing with the broader central CONUS trough and lifting
quickly northeastward towards the middle Mississippi Valley and
Midwestern states Saturday night. As this occurs, it triggers a
surface low to deepen in the vicinity of IL/WI/IA which then
quickly lifts - along with the parent shortwave - northeastward
over the Great Lakes and into southern Ontario. A cold front
associated with this low surges eastward into the Ohio Valley
and lower Great Lakes regions on Sunday. The pressure gradient
tightens between the Great Lakes surface low and an area of
high pressure over the western Atlantic, causing winds across
the local area to rapidly strengthen ahead of the cold front.
The latest NBM continues to suggest a very high probability
(>90%) for frequent wind gusts exceeding 30mph across our
entire area during the day Sunday. There are also increasing
probabilities (60-80% areawide) for occasional gusts over 40mph.
Above that, probabilities quickly drop off, with only a 10-20%
chance for gusts over 50mph.
Showers and thunderstorms are expected to develop along and
ahead of the cold front as it approaches the area late Saturday
night and moves through from west to east during the day
Sunday. Instability will most likely be weak (MLCAPE on the
order of 100-300 J/kg), but with such a potent shortwave and
associated surface low, there should be enough forcing from the
dynamics of this system to help overcome the instability
deficiency. Therefore, a few heavier/stronger showers and storms
could develop along the cold front itself, primarily during the
Noon to 8pm timeframe. Given how strong the background flow is
expected to be outside of convection (see wind discussion in
previous paragraph), it's reasonable to say that any stronger
cells could produce locally higher wind gusts that reach or
exceed 60mph. Additionally, ample low-level wind shear along
the cold front may support transient mesocyclonic structures
embedded within whatever squall line ends up forming, and thus a
low-end threat for a brief tornado or two will also exist.
With the passage of the cold front Sunday afternoon/evening,
winds shift to westerly and the severe threat ends. Winds will
diminish slightly behind the front, but breezy conditions are
expected to continue through Sunday night. Rain chances also
continue through Sunday night as a new surface low starts to
deepen over the mid-Atlantic coast and the wrap-around
precipitation on its western periphery lingers over the area.
&&
.LONG TERM /MONDAY THROUGH FRIDAY/...
KEY MESSAGES:
- Cooler weather returns next week
- Periodic rain chances through the middle of next week
-------------------------------------------------------------------
The upper trough begins to exit eastward Monday allowing height
rises as a short wave ridge slides across the region. Drier
conditions and clearing skies are anticipated Monday. High
temperatures are expected to fall back towards normal on Monday
behind our cold front and remain near to slightly below normal
through the remainder of the forecast period.
Ensembles are in rather strong agreement that another digging long
wave trough quickly chases ridging out by Tuesday. This trough
brings with it another chance for rain and possibly storms with
machine learning models even hinting at low end severe
probabilities.
After this the long wave pattern becomes a little more muddled as
ensembles diverge on where the long wave trough stalls. However,
most ensembles are in agreement that several short waves round the
base of the trough as it lingers across the eastern Great Lakes
through next week. This activity is expected to keep rain chances up
as we move late into next week.
&&
.AVIATION /21Z FRIDAY THROUGH WEDNESDAY/...
VFR conditions are expected to prevail across the region with
light winds. Mid to high- level clouds begin to increase from
the west this evening as a trough approaches the Great Lakes
region. There is a chance for light rain/drizzle to pass north
of Pittsburgh between 03Z and 12Z Saturday, though ceilings
will remain VFR given the presence of sufficient dry air in the
low levels. PROB30s for light rain and slight reductions in VFR
ceilings were included at FKL/DUJ to reflect this potential.
.OUTLOOK...
A low pressure system will move across the region Sunday,
bringing widespread precipitation and associated reductions in
cigs and vis. A strong gradient wind field accompanying this
system will likely result in increasing sfc winds after sunrise
Sunday. By mid-afternoon, thunderstorm chances will rise ahead
of the approaching cold front, and depending on environmental
conditions, some storms could reach severe criteria.
In the wake of the front, periods of rain showers, lower cigs,
and gusty winds may persist into Monday.
&&
.PBZ WATCHES/WARNINGS/ADVISORIES...
PA...None.
OH...None.
WV...None.
&&
$$
SYNOPSIS...Cermak
NEAR TERM...Cermak/Milcarek
SHORT TERM...Cermak
LONG TERM...AK
AVIATION...Cermak/Hefferan
Source: PBZ issues Area Forecast Discussion (AFD) at Oct 17, 5:18 PM EDT (https://mesonet.agron.iastate.edu/p.php?pid=202510172118-KPBZ-FXUS61-AFDPBZ)
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