PBZ issues Area Forecast Discussion (AFD) at Sep 30, 1:50 PM EDT004
FXUS61 KPBZ 301750
AFDPBZ
Area Forecast Discussion
National Weather Service Pittsburgh PA
150 PM EDT Mon Sep 30 2024
.SYNOPSIS...
Precipitation chances continue through Wednesday morning with a
departing upper low and cold front. Clearer and drier conditions
return late week, aside from a chance of rain late Friday or
early Saturday along a weak cold front.
&&
.NEAR TERM /THROUGH TONIGHT/...
KEY MESSAGES:
- Light rain south of I-80 today, and east of I-79 tonight with
patchy fog and low clouds.
-------------------------------------------------------------------
An upper low, combined with the remnants of Helene, remains
situated over northern West Virginia. Wrap-around moisture
continues to keep profiles saturated through the entire
atmosphere with ample cloud cover. An area of convergence on the
northern periphery of the low has, and will continue to allow
for rainfall today. Even this weak forcing in a profile as
saturated as it is (1.65" PWATs), has allowed warm rain
processes to dominate. A stratiform shield will remain situated
south of I-80 today with rain rates between 0.05" to 0.1" per
hour.
Overnight, the upper low is expected to rejoin the flow and
move eastward. As it does this, the main convergence zone and
rain chances reorient mainly east of I-79. All in all, the
greatest chance (50%) of seeing totals exceed 0.5" remains in
southwest Pennsylvania and northern West Virginia with the best
moisture pull.
Patchy fog is possible tonight in saturated profiles with
recent rainfall, but visibility drops are not expected to be
widespread or low and mainly realize as a low stratus deck. Some
low probability of lower drops exist for Zanesville should they
experience some clearing given calm winds. Clouds will keep
lows around 10 to 15 degrees above average.
&&
.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 MONDAY/...
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 /18Z MONDAY THROUGH SATURDAY/...
Difficult near term forecast continues with abundant moisture
and northward advection of light rain bands continuing through
the day favoring development/persistence of MVFR/IFR CIGs with
similar VIS restrictions. Some drier air noted on latest
satellite loops now working into MGW is providing scattering to
VFR conditions, and downsloping effects with an east/southeast
wind through the early afternoon has kept LBE mostly restriction
free in light rain showers.
Expect the trend to be for restrictions to MVFR and lower into
the late evening hours (save MGW) before probabilities indicate
the potential for a period of lifting to at least MVFR around
00z tonight; latest hi res guidance even provides enough drier
air to bring VFR back for PIT and surrounding terminals in the
early overnight hours, and this is supported by HREF probabilities
rapidly decreasing; confidence is low to moderate in this as
other available guidance suggests restrictions holding strong,
but upstream obs do indicate scattering with convective-type
showers.
With lingering moisture overnight from recent rainfall and no
change in airmass, thinking that once moisture socks back in for
the latter half of the overnight, persistence will be the best
forecast which has manifested boundary layer moisture as low
stratus. The exception may be for ZZV where wind overnight is
favored to be a bit calmer thanks to closer proximity to the
decaying low which may allow for VIS restrictions as well;
coincidentally, there is a ~40% for IFR VIS restrictions there
overnight contingent on calming wind.
.Outlook...
Improvement Tuesday is favored to be gradual, but do expect
that we will begin to scatter by late morning as drier air works
in from the southwest. A cold frontal passage with an incoming
upper trough expected 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...Milcarek
NEAR TERM...Milcarek
SHORT TERM...Shallenberger
LONG TERM...CL
AVIATION...MLB/AK
Source:
PBZ issues Area Forecast Discussion (AFD) at Sep 30, 1:50 PM EDT---------------
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