PBZ issues Area Forecast Discussion (AFD) at Apr 9, 6:38 PM EDT111
FXUS61 KPBZ 092238
AFDPBZ
Area Forecast Discussion
National Weather Service Pittsburgh PA
638 PM EDT Wed Apr 9 2025
.SYNOPSIS...
Rain and snow possible overnight through early morning, followed
by primarily rain chances lingering through Saturday. Temperatures
rise through Monday with dry weather, until another frontal
passage is possible early-to-mid week.
&&
.NEAR TERM /THROUGH THURSDAY NIGHT/...
KEY MESSAGES:
- Increasing clouds and precipitation chances overnight.
- Rain chances linger through Thursday night, with some
uncertainty if rain turns convective late-day Thursday.
-------------------------------------------------------------------
Made some minor adjustments to slow down PoPs through the early
overnight hours as, despite what the radar reflectivity returns
are suggesting, copious sub-cloud layer dry air below 700 mb on
recent PIT ACARS soundings is preventing rain from reaching the
ground; dew point depressions locally remain in the 20-30
degree range. Thus, a period of wet-bulbing will be necessary to
overcome the dry air, and latest HRRR/RAP data shows wet-bulb
temperatures above freezing everywhere south of I-80, so the
area with the highest chance of seeing a brief period of snow at
onset remains up in that corridor. The forecast otherwise
remains on track this evening...
A mid-level low continues to dig into the upper Ohio Valley
tonight through Thursday, forcing some surface cyclogenesis.
Low-level warm advection and lift is expected along a trough,
that will force precipitation across the area overnight. Initial
precipitation may struggle to overcome initial dry air, but it
will eventually break through by, at-least, sunrise for most.
Wet bulbing effects with temperatures near freezing may result
in an onset of snow (50% to 70%) along and north of the I-80
corridor, primarily between 3am and 9am, though accumulations
are forecast be less than 1" with 90% probability. Given
marginal or above-freezing temperatures, impacts are expected
to be limited save the potential for some slick bridges in
northern Venango and Forest County.
As the warm front and adjacent cold front pull through, rain
will be most likely in the mid-morning and early afternoon,
before the cold-core low settles in for the afternoon and
overnight period in the upper Ohio Valley. There is some
uncertainty whether precipitation ends, or if there will be
enough instability under the upper low to increase shower
chances into the evening. Should the precipitation turn more
showery, dependent on instability, there is the potential for
cold air funnels in any shallow updrafts tomorrow. Roughly 60%
of ensembles show little (<10 J/kg) or no instability with
overcast conditions favored, but there is a 10% chance of up to
100 to 150 J/kg advecting from the southwest, which when
combined with 100-200 0-1km SRH, could result in some spinning
showers. Once again, this generally remains low probability but
will warrant watching.
This environment persists into the overnight, though with the
loss of a heating component from the surface, the funnel threat
may end, though scattered showers may remain possible under the
destabilizing, cold-core low.
&&
.SHORT TERM /FRIDAY THROUGH SATURDAY/...
KEY MESSAGES:
- Rain chances linger through Saturday.
- Wrap around snow possible Saturday in the highest terrain.
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A reinforcing shortwave is expected to dig into the upper-
Midwest, rounding the trough, and forcing secondary low
development in the southern Appalachians. This mid-level forcing
may briefly make for a secondary closed low, before an
elongated area of closed flow develops along the east coast.
This will, in turn, bring the surface low up along its eastern
flank, overspreading rain from Georgia to Maine.
In the current forecast, the main low track utilizing the best
moisture and forcing is to the east of the Appalachians, but
depending on upper low placement, there is still a 10% chance
the low could sit farther east and drop up to 1.5" along the
high terrain , with up to an 1" in Pittsburgh. This would lead
to more marginal flooding threats, but again, this remains only
10% probable, with the rest of the ensembles taking the main
storm to the east.
Some snow is again possible in the highest terrain Saturday with
cold air wrapping around the backside of the low. Since most of
this is forecast during the day with marginal freezing
temperatures, no impacts are expected, pockets of eastern Tucker
could see more than 1" if the snow rates remain high enough
with orographic enhancement.
&&
.LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/...
KEY MESSAGES:
- Uncertainty in early-to-mid week cold frontal passage.
-------------------------------------------------------------------
Ensemble clustering is much more confident in the upper low
departure late Saturday into Sunday with ridging through Sunday
and Monday, which will warm temperatures back up to near/above
normal. By late Monday, the next trough is forecast to pass,
though there is timing uncertainty with the trough and adjacent
cold front, which would allow the next chances of rain and a
cool down. By Tuesday at 8pm, roughly 60% of the ensemble
guidance has eastern troughing behind a cold front, and 40% has
a continued ridge. Should the trough pass, there is also
uncertainty as to the strength of the trough and cold.
By Wednesday and into late next week, uncertainty decreases yet
again with almost all ensembles and clusters showing that the
trough has passed, with building ridging yet again.
&&
.AVIATION /22Z WEDNESDAY THROUGH MONDAY/...
VFR is expected through early this evening as high pressure
moves east across the region, though mid and high level clouds
will increase ahead of an approaching warm front.
Low pressure will track eastward across the Midwest tonight, as
the associated surface warm front lifts slowly north across the
Upper Ohio Valley region. Rain is expected to overspread the
region as the front approaches, with a gradual deterioration to
MVFR later tonight. Areas near and north of I 80 will likely see
a period of snow, or a rain/snow mix, with IFR conditions.
Any snow will change to rain Thursday morning, with MVFR
continuing in rain. The rain will likely taper to showers during
the day following the passage of the warm front.
Outlook...
Restrictions ar expected through Thursday night in rain as low
pressure crosses the region. Restrictions are likely to
continue, along with rain and snow showers, Friday through
Saturday night as an upper low drifts across the region. VFR
returns Sunday under high pressure.
&&
.PBZ WATCHES/WARNINGS/ADVISORIES...
PA...None.
OH...None.
WV...None.
&&
$$
SYNOPSIS...Milcarek
NEAR TERM...MLB/Milcarek
SHORT TERM...Milcarek
LONG TERM...Milcarek
AVIATION...WM
Source:
PBZ issues Area Forecast Discussion (AFD) at Apr 9, 6:38 PM EDT---------------
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