306
FXUS61 KPBZ 210101
AFDPBZ

Area Forecast Discussion
National Weather Service Pittsburgh PA
801 PM EST Thu Nov 20 2025

.SYNOPSIS...
Rain favoring areas south of Pittsburgh is expected by Friday
evening and continuing into Saturday morning. Dry and seasonable
weather is likely Sunday into Monday before the next low
pressure system brings widespread rain Tuesday.

&&

.NEAR TERM /THROUGH FRIDAY/...

- More localized dense fog potential overnight.
---------------------------------------------------------------

..8pm Update..

Given a very light prevailing westerly wind and surface
convergence over the ridges, dense fog has been observed to the
east of Pittsburgh. Frequent observations of quarter mile fog
have been observed, confirmed by PA-511 webcams through Laurel
Summit and Jefferson County. Given no sign of improvement
overnight with cooling and further establishment of a nocturnal
inversion, pushing dew point depressions toward zero, a dense
fog advisory runs through 14Z with diurnal clearing. This may
need to be expanded overnight depending on any future formation.


..Previous Discussion..

A fairly stagnant, moist air mass is likely to remain in place
through the overnight period with minimal surface flow and
weaker zonal flow aloft. Cloud cover is likely to persist (even
if its not lower stratus, mid to upper level decks will be in
place) save for areas around/north of I-80 that may experience
enough subsidence from a New England high to create some breaks.
This should limit the diurnal temperature curve and keep
readings below the daily average (seeing approximately another
5 degrees of heating the rest of the day).

Subtle positioning differences of the New England high may
foster weak southerly flow overnight, but the impacts of this
are unlikely to alter the prevailing conditions. Expect cloudy
conditions with limited nocturnal cooling. Fog can`t be ruled
out but abundant stratus should limit development of widespread
dense fog. Any fog that develops may favor the higher terrain
east of Pittsburgh due to some sfc convergence.

&&

.SHORT TERM /FRIDAY NIGHT THROUGH SATURDAY NIGHT/...
KEY MESSAGES:

- Wetting rainfall returns Friday, highest amounts south of
  Pittsburgh
- Drying out Saturday with seasonable temperatures
----------------------------------------------------------------

Surface high pressure pushes offshore of New England early Friday
ahead of our next chance for rain arriving in the morning hours. Low
pressure ejects out of the south-central US and moves quickly
through the Ohio Valley out ahead of a closed mid-level low that
flattens and rejoins zonal flow. This will overspread rain to the
area starting Friday morning as the associated east-west oriented
warm front sets up likely south of Pittsburgh. Moisture return ahead
of it bumps PWAT values to near 1", and the highest PoPs are carried
Friday evening into the overnight hours when a weak coupled mid-
level jet structure with right entrance and left exit region overlap
locally. Rainfall totals will feature a north-south gradient with
highest amounts to the south. Latest ensemble runs and GEFS/ECMWFE
AI models continue to favor a southward shift in the precip shield,
most all farther south than the NBM. Some of the available CAMs
follow a similar trend with even no measurable rain north of
Pittsburgh at all, though think that they might be under-doing
the stratiform component driven by the synoptic forcing and that
at least light rain should stretch farther north than they
advertise. The wetter end of the goal posts for Pittsburgh sits
at around three quarters of an inch while the dry end suggests
very little. Most likely is around a tenth to a quarter of an
inch. Farther south, probability for >0.5" peaks around 70%
south of I-70. North of Pittsburgh, the chance of even reaching
0.25" is only around 20-40%, and if AI models are right, this is
where we may see a further decline in totals. Flooding is not
expected to be a concern with light rainfall rates.

The low makes its exit Saturday morning, though some showers may
linger in the ridges into the early afternoon as the shortwave
completes its passage. Dry air arrives in its wake both in the mid-
levels and at the surface with northerly surface flow as high
pressure builds across the area. Clouds will erode Saturday
afternoon with some sun possibly peeking through.

&&

.LONG TERM /SUNDAY THROUGH THURSDAY/...
KEY MESSAGES:

- Dry Sunday and Monday
- Active pattern returns by mid-week with passing low pressure, but
  confidence in any local impacts remains low
-------------------------------------------------------------------

The pattern remains amplified to close out the weekend and open the
next work week as another upper trough dives through the Northeast.
Transient ridging will move through locally on Monday with high
confidence, though exact timing remains more uncertain with
discrepancy in the departure of the trough. A quicker departure
could favor highs into the low 50s while slower points toward mid to
upper 40s, but either way, dry conditions.

That trend will be short lived as ensembles all favor another
ejecting mid-level trough and surface low through the central US by
Tuesday. The pattern is relatively high confidence, but the details
remain all over the place with timing and depth of the responsible
trough. Low pressure likely passes through our area sometime Tuesday-
Wednesday and returns precip chances with then possible wrap around
precip continuing into the end of the week, but the low`s track and
timing is very uncertain lending low confidence impacts locally.
Speculation has started to spread regarding a potential impactful
storm around the Thanksgiving holiday, but the takeaway message here
is that entirely too much uncertainty exists among ensemble members
as well as AI guidance with varying cold and warm solutions to latch
on to any specific model run at this time, especially those showing
very high snow totals; one outcome showing impactful snow
accumulation is just one of many, many potential outcomes, and a
vast majority of others point toward much lesser amounts or even all
rain. Our best chance for any snow would likely be the end of the
week with wrap around cold air behind the departing low pressure.
We`ll continue to monitor and narrow the possibilities as subsequent
model guidance attempts to better capture the evolution.

&&

.AVIATION /00Z FRIDAY THROUGH TUESDAY/...
The stagnant pattern in place across the area will allow for the
development of stratus and fog this evening and through the
overnight. There was some clearing in the north during the
daytime and this allowed for rapid cooling once the sun went
down allowing for additional fog development. Expect MVFR
conditions to worsen to IFR and below going through the night.
In fact, a DFA has already been issued and will likely need to
be extended to other locations.

Approaching low pressure Friday morning may foster enough lift
for SW to NE cig improvements before overrunning air of the lows
warm frontal boundary maintains MVFR/IFR cigs through the day.
Rain chances are more likely after the TAF period, but a brief
sprinkle or period of light rain can`t be ruled out after 12z
Friday.

Outlook...
Rain is favored to overspread the area Friday afternoon into
Saturday morning with the greatest restrictions/rainfall
accumulations occurring around/south of Pittsburgh. MVFR/IFR
will be highly likely in areas of rain, with potential for near
VFR conditions on the northern periphery if rain doesn`t develop
(FKL/DUJ).

There is high confidence of VFR under the influence of high
pressure beginning Sunday morning until the next low pressure
system arrives near Tuesday.

&&

.PBZ WATCHES/WARNINGS/ADVISORIES...
PA...Dense Fog Advisory until 9 AM EST Friday for PAZ016-074-
     076>078.
OH...None.
WV...None.

&&

$$

SYNOPSIS...Frazier
NEAR TERM...Frazier/Milcarek
SHORT TERM...MLB
LONG TERM...MLB
AVIATION...Frazier/Shallenberger