566
FXUS61 KPBZ 300908
AFDPBZ

Area Forecast Discussion
National Weather Service Pittsburgh PA
508 AM EDT Mon Sep 30 2024

.SYNOPSIS...
An upper level low will drift northeastward from Kentucky to the
Atlantic coast through Tuesday, keeping unsettled weather and
near to just above normal temperatures. A frontal passage by
Wednesday will bring drier weather and seasonable temperatures
to close out the week.

&&

.NEAR TERM /THROUGH TONIGHT/...
KEY MESSAGES:

- Mostly light rain continues tonight and into the day tomorrow,
  primarily south of Pittsburgh.
-------------------------------------------------------------------

5am update...
Minor adjustments to account for northward push/development of
light rain band stretching from Guernsey County through west
central PA this morning. The rest of the forecast remains on
track.

Previous Discussion...

The low aloft will continue to meander across the Ohio Valley
through dawn and into the coming day. The best PoPs through dawn
will be near and south of Pittsburgh as the best convergence
shifts to this region. The abundant cloud cover will help keep
diurnal ranges small, with lows some 10 to 15 degrees above
climatology.

The upper low starts to make some eastward progress on Monday as an
upstream shortwave trough over the northern Plains starts to nudge a
Great Lakes ridge axis eastward, causing the upper low to start to
eject. PoPs will show a north-to-south positive gradient into Monday
night, following the pattern of best moisture and low-level
convergence. Instability gets shunted south of the region per the
HREF, and thus thunder is less likely. The lack of convection will
create a more uniform QPF pattern. Chances of exceeding 0.25" over
the Monday/Monday night period are maximized at 60-70% along the
southeast ridges.

&&

.SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/...
KEY MESSAGES:

- Continued rain chances with seasonably warm lows and
  seasonable highs.
-------------------------------------------------------------------

The Tuesday/Tuesday night period will be a transition period.  The
upper low will slowly degrade as it lifts to the northeast,
eventually reaching the Atlantic Coast by 00Z Wednesday as an open
trough.  Meanwhile, the northern stream shortwave will be crossing
the Great Lakes, pushing a cold front in our direction.  The most
likely time for FROPA appears to be Tuesday night, with a slight
delay into Wednesday possible. Showers are most likely Tuesday to
the southeast of Pittsburgh in the path of the upper low, but cannot
be totally ruled out anywhere.  Much of the region can expect a
mostly cloudy sky for a good portion of the day though. PoPs Tuesday
night with the front will be highest north of Pittsburgh, with left
exit region jet dynamics potentially playing a role. Fast movement
overall should keep rain totals in check.

With a few cloud breaks possible, and with the departure of the
upper low, Tuesday highs may tick up a couple degrees as compared to
Monday, with lower but still warmer-than-normal lows at night with
the frontal passage. The cold front will complete its passage on
Wednesday if it has not already done so by Tuesday night. This
will usher in some drier and cooler air as temperatures will be
near or just below normal for Wednesday. Dry conditions are
expected as well.

&&

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

- A cold front passage is expected by early Wednesday, bringing
  an end to rain chances.
- An overall drier and less cloudy pattern is expected into next
  weekend.
-------------------------------------------------------------------

Expect a more quasi- zonal flow pattern takes hold through next
weekend. Overall, this appears to be a fairly dry period as
access to southern moisture remains mostly cut off. Still, some
model solutions suggest that a weak front may provide isolated
showers around Friday night.

Temperatures are showing more uncertainty, as 500mb heights over our
region will ultimately depends on upstream developments over the
western CONUS.  Model clusters are showing various ridge/trough
scenarios that could cause highs/lows to stray a bit further from
climatology than the current forecast.  However, given the overall
zonal pattern and until a more clear signal emerges, will keep
temperatures not too far from normal values overall.

&&

.AVIATION /09Z MONDAY THROUGH FRIDAY/...
Difficult near term forecast as region remains under the
influence of Hurricane Helene remnants and the broad area of low
pressure sitting to the SW.

Abundant moisture and northward advection of light rain bands
favor development/persistence of MVFR/IFR cigs with only minor
vsby restrictions through the day. A weak pocket of drier air
within ESE flow aiding VFR conditions around KPIT as of 09z, but
guidance favors filling in of cigs. Diurnal heating and weak
lift may allow for some cig improvements during the afternoon
before moisture convergence on the north side of the low returns
MVFR/IFR conditions.

.Outlook...
Further drifting of the upper low east Tuesday will offer
potential for VFR conditions around KZZV. Otherwise, MVFR/IFR
cigs with periods of light rain are expected to persist until a
cold frontal passage with incoming upper trough late Tuesday
night.

An air mass change after fropa will offer dry weather and VFR
conditions by Wednesday afternoon through the end of the week.

&&

.PBZ WATCHES/WARNINGS/ADVISORIES...
PA...None.
OH...None.
WV...None.

&&

$$

SYNOPSIS...CL
NEAR TERM...Frazier/Shallenberger
SHORT TERM...Shallenberger
LONG TERM...CL
AVIATION...Frazier