PBZ issues Area Forecast Discussion (AFD) at Sep 30, 3:51 PM EDT343
FXUS61 KPBZ 301951
AFDPBZ
Area Forecast Discussion
National Weather Service Pittsburgh PA
351 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 /UNTIL 6 AM TUESDAY MORNING/...
KEY MESSAGES:
- Light rain south of I-80 today, and east of I-79 tonight with
patchy fog and low clouds.
-------------------------------------------------------------------
A band of more moderate precipitation over Pittsburgh for the
last couple hours has led to totals toward the higher end of the
distribution. As of 3:45pm, totals are around 0.75" for some and
may near an inch through tonight. Elsewhere, totals are
generally near 0.25" to 0.5".
.. Previous Discussion ..
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 /6 AM TUESDAY MORNING THROUGH WEDNESDAY NIGHT/...
KEY MESSAGES:
- Continued rain chances with seasonably warm lows and
seasonable highs.
-------------------------------------------------------------------
The upper low will gradually pull to the east throughout the
day, tapering rain chances in the morning before shower
potential increases into the afternoon, largely a result of
heating and convergence ahead of a approaching cold front.
Coverage and totals will remain low with high confidence. With
mixing, some overcast decks may break out into the afternoon,
most likely in eastern Ohio. This may allow highs to get around
5 degrees above average in eastern Ohio, with more seasonable
highs elsewhere.
The cold front is expected to pass early Wednesday morning with
high confidence. Precipitation chances are highlighted along
the frontal axis. Showers are expected to be brief and fast
moving, with little to no additional precipitation expected. The
most noticeable change behind the cold front will be lower
humidity and clearing skies. This will leave Wednesday quite
comfortable.
Wednesday night, clear skies behind the cold front will allow
lows to get back to "seasonable levels" (aka much cooler than
what we have been seeing). Recent rains and efficient cooling
will likely result in fog formation.
&&
.LONG TERM /THURSDAY THROUGH MONDAY/...
KEY MESSAGES:
- Drier and clearer.
- Slight chance rain/clouds late Friday or early Saturday.
-------------------------------------------------------------------
The theme of the period is drier and clearer. High pressure and
subsidence are expected to dominate, keeping conditions much
more comfortable. Small height rises into Thursday and Friday
may allow temperatures up to 10 degrees above normal for this
time of year. Temperatures cool slightly into the weekend behind
a weak cold front, which will also bring a slight chance of
rain and increases in clouds.
Uncertainty increases next week. While there is around an 80%
chance of troughing, ensembles are quite deviant on the
strength and position which would influence temperature and
precipitation patterns. Under most scenarios, highs are
enveloped between the 60s and low 70s, with the best chances for
precipitation late Sunday into Monday. This is far from a
guarantee with alternate scenarios being weak quasi-zonal flow
to the main trough axis to the east. Much of the uncertainty is
rooted in the strength and position of a western ridge. Once
agreement is reached on this, predictability will increase.
&&
.AVIATION /20Z 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...Milcarek
LONG TERM...Milcarek
AVIATION...MLB/AK
Source:
PBZ issues Area Forecast Discussion (AFD) at Sep 30, 3:51 PM EDT---------------
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