PBZ issues Area Forecast Discussion (AFD) at Sep 28, 1:39 PM EDT956
FXUS61 KPBZ 281739
AFDPBZ
Area Forecast Discussion
National Weather Service Pittsburgh PA
139 PM EDT Sat Sep 28 2024
.SYNOPSIS...
A large upper level low will drift eastward this weekend
reaching the Mid-Atlantic region by Monday. This will keep our
weather unsettled through the beginning of next week but
temperatures remain mild.
&&
.NEAR TERM /THROUGH TONIGHT/...
KEY MESSAGES:
- Scattered showers continuing through the overnight hours.
- Lows well above normal.
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Upper level low pressure will continue to sit across Tennessee
and Kentucky throwing weak impulses around it. Water vapor
imagery indicates that moisture is working back into our region
in the wake of the early morning dry slotting and will continue
to do so for the remainder of the day. This broad, weak forcing
will allow for maintenance of scattered showers with highest
probability west of I-79 coincident with the better deep layer
moisture. With the overall weak forcing and limited instability,
not expecting any prolific rainfall production today with
ensemble probability for >0.25" by Sunday morning around 40-60%
in eastern OH and 20-40% further west.
Not expecting much of a diurnal range with lows tonight dipping
into the mid 60s owing to a blanket of cloud coverage, low level
moisture, and weak easterly flow all acting against efficient
cooling. Lingering boundary layer moisture will likely manifest
mostly as stratus overnight, but wouldn't be surprised to see some
reduced visibility in light rain/mist.
&&
.SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/...
KEY MESSAGES:
- Cloudy with light rain chances.
- Temperatures around seasonal normals.
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The stacked low will continue to hold influence on our weather
locally as it exhibits little movement into early next week.
Broad ascent with weak shortwave movement around it and an
increase in moisture will fuel scattered rain shower chances
again on Sunday. Amounts look to be light with overall weak
forcing, and probability for >0.25" is between 50-70%. Some
localized higher totals are possible especially across southeast
OH/northern WV where some instability may be able to develop
(30% chance of >500 J/kg) but this is contingent on any amount
of clearing which appears lower probability at this time given
the deep layer moisture in place. Still, the potential is there
with up to a 30% chance of 1 hour rates exceeding 0.5".
Come Monday, ensembles begin to absorb the low back into the flow,
albeit slowly as it gradually shifts east through the day and
transitions back to an open wave. Rain chances will continue into
the day as the low undergoes cyclolysis with highest chances now
shifting south of I-80 and coincident with the best forcing and
moisture. Highest rainfall amounts will likely be confined to the
ridges where there is a 60-80% chance of >0.25" for the 24 hour
period ending Monday night with lower totals elsewhere.
Temperatures overall will be around average through early week with
cloud coverage and showers.
&&
.LONG TERM /TUESDAY THROUGH FRIDAY/...
KEY MESSAGES:
- Rain chances continue into Tuesday night ahead of a mid-week cold
front.
- Drier weather behind the front to close out the week.
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What's left of the low will be kicked off to the east on Tuesday as
a strong shortwave trough digs across the northern Plains and into
the Great Lakes region. Seeing some differences with the timing and
amplitude of said trough among the clustered ensembles; a solution
with a weaker, quicker trough and brief shortwave ridging would end
rain chances sooner, sometime Monday night, while a less progressive
one maintains rain chances further west into Tuesday morning. At
this point will maintain highest rain chances south and east of
Pittsburgh where most guidance advertises at least measurable
amounts. Nearly 60% of the QPF distribution for Pittsburgh through
00z Wednesday falls below 0.10" with a tail extending up to a half
an inch or so representative of a slower trough progression.
Either way, a cold front will dive out of the Great Lakes overnight
Tuesday night into Wednesday morning reintroducing rain chances for
most of the area. Unfavorable diurnal timing and displaced upper
forcing will limit rain totals/thunder mention as we would need a
deeper trough which is a possible, but low probability, solution to
enhance precip totals; even 90th percentile NBM QPF advertises
up to a tenth or two.
A much drier, cooler airmass settles in for the latter half of the
week, though temperatures are favored to rebound by the end of the
period to above climatology.
&&
.AVIATION /18Z SATURDAY THROUGH THURSDAY/...
VFR conditions are forecast to continue for the most part into
the evening hours, although DUJ is stubbornly holding on to low
ceilings in easterly flow. East-to-southeast wind around 10
knots is expected to continue. Increasing moisture rotating
around a Middle Ohio Valley upper low may provides some light
rain showers to eastern Ohio, including ZZV, this afternoon.
As the upper low elongates and slowly oozes up the Ohio Valley,
moisture will continue to increase, with nocturnal cooling
leading to falling ceilings and the development of a light mist.
Most terminals will see ceilings fall into the IFR range
overnight, save for perhaps MGW, where ongoing easterly flow may
prevent such restriction. Light rain showers are expected after
06Z as well, although visibility should remain in the MVFR
category for the most part.
Restrictions will likely linger through the end of the TAF
period, with modest improvement to MVFR possible by midday,
mainly south of I-80 and away from the ridges. Light easterly
surface wind will linger.
.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...22/MLB
NEAR TERM...MLB
SHORT TERM...MLB
LONG TERM...MLB
AVIATION...CL
Source:
PBZ issues Area Forecast Discussion (AFD) at Sep 28, 1:39 PM EDT---------------
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