PBZ issues Area Forecast Discussion (AFD) at Sep 29, 1:56 AM EDT038
FXUS61 KPBZ 290556
AFDPBZ
Area Forecast Discussion
National Weather Service Pittsburgh PA
156 AM EDT Sun Sep 29 2024
.SYNOPSIS...
A potent upper low will remain stagnant over Kentucky through
early next week, keeping conditions mild, unsettled, and
cloudy. A frontal passage Wednesday will act to clear and dry
much of the northeast.
&&
.NEAR TERM /THROUGH TODAY/...
KEY MESSAGES:
- Seasonably warm temperature with rain chances.
-------------------------------------------------------------------
The remnants of Helene remain collocated under an upper low
that is forecast to remain over Kentucky through the near-term
period. Locally, this means southeasterly flow, that has
advected, and will continue to advect, Atlantic and Gulf
moisture around the circulation. Given the homogeneous
environment, precipitation chances and lulls will remain tied to
subtle shortwaves pivoting around the upper low. Some enhanced
deformation has also been observed just to the north leading to
deeper convective structures, but higher rain rates have not
been observed across our forecast area.
The most likely area for continued precipitation through morning
is expected to be tied to a wave and localized convergence in
eastern Ohio and western Pennsylvania. A similar zone of weak
upper forcing and convergence is expected Sunday, most likely
south of I-80. All in all, total additional precipitation
through eastern Ohio has a 60% to 90% chance of exceeding a
0.25" of rain, while chances drop slightly to 30% to 60% for
western Pennsylvania and northern West Virginia. Most to all of
this is expected in light rain and drizzle with little to no
instability.
Elevated dew points are expected to keep temperatures above
average, particularly tonight. With ample upper moisture,
overcast skies will dominate.
&&
.SHORT TERM /TONIGHT THROUGH MONDAY NIGHT/...
KEY MESSAGES:
- Continued rain chances with seasonably warm lows and
seasonable highs.
-------------------------------------------------------------------
Rain chances continue Sunday night, mostly confined to south of
I-70 in an area of convergence on the long axis of the oblong
upper low. Ample cloud cover in upper moisture will keep low
temperatures around 10 to 15 degrees above normal.
The upper low begins to slowly progress east throughout the day
as it rejoins with the flow pattern. Once again, surface
converge and deformation on the north side of the decaying low
will allow daytime rain chances, mostly south of I-80. Profiles
remain saturated; highs may remain a bit closer to seasonal
normals. This pattern continues into Monday night with lows 10
to 15 degrees above average once again with ample cloud cover.
Additional QPF totals are variable. Chances of exceeding 0.25"
are as low as 30% to 50% for the I-80 corridor, and as high as
70% to 90% for northern West Virginia.
&&
.LONG TERM /TUESDAY THROUGH SATURDAY/...
KEY MESSAGES:
- Transitory pattern Tuesday before a passing front Wednesday.
- Drier and less cloudy to close out the week.
-------------------------------------------------------------------
Tuesday will leave the are in between the influence of the
upper low and ahead of an incoming cold front. PWATs will drop,
owing mostly to dry air aloft, but there still may be enough
moisture to maintain a cloud deck and some showers, most likely
for the ridges of WV closes to the departing low. There is
uncertainty in cloud coverage that may influence uncertainty in
daytime highs, though the most likely scenario is overcast to
broken decks with highs a few ticks above normal.
There remains relatively high confidence in a cold frontal
passage sometime on Wednesday, which will act to introduce a
notably drier and cooler airmass. The amount of QPF with the
frontal passage will depend on the time of day, with a later
passage allowing for more instability generation. The most
likely scenario at this point is a passage in the morning with
minimal additional rainfall, especially when combined with its
fast motion.
Flow then transitions quasi-zonal, with the main uncertainty
late- week in the N/S placement of the upper jet. This comes
from a divergent representation of weak western troughing or
ridging, which would correspond to the opposite pattern in the
east. This will mainly affect temperatures; highs remain
enveloped between the upper 60s and lower 80s. Regardless, the
pattern favors drier and less cloudy conditions.
&&
.AVIATION /06Z SUNDAY THROUGH THURSDAY/...
Overnight rain rates within the stratiform rain are not likely
to yield noteworthy drops in vsby (MVFR at worst, likely, as
pcpn is mostly in the form of drizzle), with restrictions
derived mainly from a decrease in cigs after 29/03Z. Probability
of cigs below 1kft are high (>70%) at most terminals, except
LBE/MGW (where probability is considerably lower (<20%) of sub-
MVFR cigs as a result of position in the warm sector). PIT/AGC
will be located in the gradient between low cigs and the warmer
air to the south, with probability of cigs below 1kft around
50-60%.
Ceilings could drop as low as 400-600ft by early morning, but
will increase steadily thru the morning as warm, better-mixed
air slowly migrates nwd. Although cigs likely will rise to MVFR
(1-2kft) by early afternoon, convective mode will become more
common, with potential for vsby restrictions in higher rain
rates within any showers.
Model signals suggest lesser coverage of precipitation in the
afternoon as focus shifts once again to ern OH before pcpn
spreads into the region again Sun evening.
.Outlook...
Occasional restrictions are possible into early next week
as upper-level low pressure drifts across the Upper Ohio
Valley.
&&
.PBZ WATCHES/WARNINGS/ADVISORIES...
PA...None.
OH...None.
WV...None.
&&
$$
SYNOPSIS...Milcarek
NEAR TERM...Milcarek
SHORT TERM...Milcarek
LONG TERM...Milcarek
AVIATION...Kramar/Shallenberger
Source:
PBZ issues Area Forecast Discussion (AFD) at Sep 29, 1:56 AM EDT---------------
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