Upper Saint Clair, Pennsylvania Weather Forecast Discussion

051
FXUS61 KPBZ 260954 AAA
AFDPBZ
Area Forecast Discussion...UPDATED
National Weather Service Pittsburgh PA
554 AM EDT Fri Sep 26 2025
.SYNOPSIS...
The last of the showers are expected to exit the region this
morning. Besides the dense fog across the area, expect clearing
and dry conditions across the area through the morning. Another
low pressure system may bring additional precip to the southeast
portion of the forecast area by Saturday.
&&
.NEAR TERM /THROUGH TONIGHT/...
KEY MESSAGES:
- Drier, warmer for today
- Fog is likely to persist through 10am; Possible again tonight
---------------------------------------------------------------
Update...
Further expanded the Dense Fog Advisory to include Allegheny and
Westmoreland, where fog was rapidly filling in behind the
clearing.
Previous discussion...
The current conditions across the area this morning feature the
500MB trough finally beginning to cross the forecast area
through dawn. This will bring an end to the last round of
showers moving through the area. Lingering precip chances will
be in the northern WV region through noon. That said, the
morning concern is when the fog will begin to lift this morning.
In fact the NBM probs would suggest a complete clearing in fog
by 14Z or 15Z.
Heading into the coming day, besides the exiting rain threat,
conditions will begin to clear out with warmer temperatures
through the day. Heading into tonight, there will likely be
another fog threat with the main impact being over the northern
counties. That being case due to a low pressure system tracking
up the coast and will spread cloud cover over the southern
portion of the forecast area. It remains to be seen if another
Dense Fog Advisory would be needed. Low temperatures tonight
will be about 5 degrees warmer than normal.
&&
.SHORT TERM /SATURDAY THROUGH SUNDAY/...
KEY MESSAGES:
- Potential moisture influx Saturday could lead to showers
  southeast of Pittsburgh
- Dry conditions return for Sunday, warmer too
----------------------------------------------------------------
The Saturday period will feature a low pressure system tracking
up the east coast. The low will advect moisture over the ridges
and into the southeastern portion of the forecast area. There
is some question to the track and how well moisture will make it
over the Appalachian Range. That said, the NBM pros are giving
between 30% and 40% for 0.25 inches or more of precip over the
northern WV area. The southern PA counties along the WV border
give a paltry 20% for 0.25 inches. The low will lift off to the
northeast by Saturday night into Sunday. The cloud cover of the
exiting low will likely keep any fog from developing Saturday
night, at least keep widespread dense fog from developing. The
additional cloud cover will keep the southeastern counties quite
insulated, and in that case, warmer than normal. This is 5 to
10 degrees warmer than normal but mainly for the southeastern
counties in northern WV and southern PA.
By Sunday, high pressure is expected to take control with a
period of dry weather expected. Temperatures will be on the warm
up as well for Sunday. The impact of clearing skies will keep
temperatures almost 10 degrees above normal.
&&
.LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/...
KEY MESSAGES:
- Larger variance period that will be predicated on coastal low
  and tropical movement along the Atlantic Coast
------------------------------------------------------------------
Ensemble cluster analysis shows forecast outcomes to begin
diverging notably Sunday into early next week due to large
variance in the development/path of a Carolina coastal low AS
WELL AS whichever way tropical storm develops occurs in the
western Atlantic. At this time, the two more likely scenarios
are: the low/southeast trough remains stationary and draws rain
showers to the southeast portion of the CWA while increased
cloud cover limits diurnal heating; strong ridging builds over
the Great Lakes that shunts tropical action south/east and
maintains dry weather with temperature trending well above
normal.
The current forecast more straddles these two scenarios so there
likely will be changes in the coming days to trend both
temperature/precipitation chances up/down if and when model
output begins to converge on the most likely solution.
&&
.AVIATION /10Z FRIDAY THROUGH TUESDAY/...
Scattered showers and cloud cover continue across the area with
a crossing upper trough. These clouds have kept low stratus and
fog from developing so far tonight. Clearing was occuring behind
the trough axis, and with low level moisture in place, expect
IFR to LIFR fog and stratus to develop through early this
morning.
A gradual improvement through MVFR to VFR is expected as mixing
begins after sunrise. CU rule and model soundings indicate a
broken diurnal cumulus layer should persist through the day,
until diminishing around sunset. Mid and high level clouds will
likely increase overnight on the northern side of a wave of low
pressure across the Carolinas/Mid Atlantic region. This cloud
cover could result in less fog development Friday night.
.OUTLOOK....
Restrictions in showers are possible Saturday mainly SE of PIT
as a surface low low tracks NE along the coast. Otherwise, VFR
is expected through early next week under high pressure.
Restriction potential returns SE of PIT Tuesday ahead of a
coastal low.
&&
.PBZ WATCHES/WARNINGS/ADVISORIES...
PA...Dense Fog Advisory until 10 AM EDT this morning for PAZ007>009-
     013>016-020>022-029-073-074-077-078.
OH...Dense Fog Advisory until 10 AM EDT this morning for OHZ039>041-
     048>050-057>059-068-069.
WV...Dense Fog Advisory until 10 AM EDT this morning for WVZ001>004.
&&
$$
SYNOPSIS...Shallenberger
NEAR TERM...WM/Shallenberger
SHORT TERM...Frazier/Shallenberger
LONG TERM...Frazier/Shallenberger
AVIATION...WM

NWS PBZ Office Area Forecast Discussion