PBZ issues Area Forecast Discussion (AFD) at Jul 10, 1:45 AM EDT322
FXUS61 KPBZ 100545
AFDPBZ
Area Forecast Discussion
National Weather Service Pittsburgh PA
145 AM EDT Wed Jul 10 2024
.SYNOPSIS...
The remnants of Hurricane Beryl may bring showers and
thunderstorms to the area overnight tonight and tomorrow. Some
could pose a damaging wind and tornado risk. Wednesday will be
another hot day with heat indices approaching 100 degrees in
portions of the region.
&&
.NEAR TERM /THROUGH TODAY/...
KEY MESSAGES:
- Marginal Risk (1/5) for severe overnight in eastern Ohio and
northwest Pennsylvania.
-------------------------------------------------------------------
No major changes for the evening update. PoPs have been
adjusted in line with the latest hires models. Greatest threat
for any convection overnight remains in Ohio and parts of NW PA.
Overnight lows were adjusted but remain very warm.
Previous discussion...
A Marginal Risk (1/5) for severe continues for a small sliver
of our eastern Ohio counties and extending into northwest PA as
a warm front lifts north through the Ohio Valley late tonight.
Wind and few tornadoes would be the primary threat; that said,
the majority of forecast soundings from the CAMs suggest a
stable surface given the poor diurnal timing. Dynamics won't be
an issue as plenty of low level shear will be present as Beryl
gets closer, but the chance of a storm rooting at the surface
and subsequently posing a wind or tornado threat is low
probability. Otherwise, we should see a limited severe threat
with mid level lapse rates not all that favorable and limited
deep layer instability as moisture increases through the depth
of the column. In addition, the warm, moist airmass will
continue tonight, providing little relief with a 70-90% chance
of lows >70F and a 40- 50% chance of >75F.
&&
.SHORT TERM /TONIGHT THROUGH THURSDAY NIGHT/...
KEY MESSAGES:
- Remnants of Beryl track near the area beginning on Wednesday.
- Dry slot will prohibit widespread rain but scattered
thunderstorms possible.
- Slight Risk (1/5) of severe for far northeastern areas and
Marginal Risk (1/5) for Pittsburgh and east.
- Hot with heat indices in the upper 90s to near 100.
-------------------------------------------------------------------
The remnants of Beryl approach and impact the area starting on
Wednesday. Ensembles have now resolved to better agreement on a dry
slotting solution that will significantly reduce rainfall chances
and amounts across most of the area. Latest NBM and HREF
probabilities for even >0.5" by Wednesday night are only ~50%
north of I-80 (~25% at PIT) coincident with the intrusion of a
remarkably sharp dry slot (ensemble mean 500 mb RH values drop
from the 80% range to single digits in 3-6 hours); coverage is
very likely going to take on a scattered, convective nature.
Can't rule out some very localized hydrology concerns in the far
northern part of our CWA, but confidence on this is rapidly
decreasing and thus the Slight Risk for excessive rainfall has
been removed in favor of a Marginal Risk from I-80 and north. We
may even raise heat concerns on Wednesday, especially south and
east of Pittsburgh, as low level moisture surges with dew
points into the low to mid 70s. and MaxTs in the low 90s. Highs
could jog a degree or two either direction if cloud cover
manifests a bit more widespread or clearer than currently
forecast, but trends are toward clearer. Mixing and tapping into
a 30-40 kt wind at 850 mb may result in gusts up to 30 mph at
times.
For the severe threat, the points of interest will be the continued
northward moving warm front that brought a conditional severe threat
overnight Tuesday night, how long the area remains in the open warm
sector ahead of a surface trough/surge of very dry mid level air,
and additional development along said "boundary." The first
possible severe risk could be focused along the warm front as it
continues its northward trek through the area in the morning
and parks north of the PA/NY border. This would be in the very
early morning hours of Wednesday and pose a conditional tornado
threat if any storms can fire along it. This might be the
timeframe of the most potent atmosphere we see as low level flow
veers and 0-1 SRH values rise above 150 m2/s2, but, CAMs show
very little interest in convective initiation and any that does
might not be surface based anyway. Our better chance for
development looks to come in the wake of the warm front during
our couple hour residence time in the warm sector during the mid
to late morning hours just ahead of the punch of bone dry mid
level air. Plenty of shear will still be available and with a
drier atmosphere, we'll see more insolation, thus greater
instability, and another shot at a conditional tornado and wind
risk. Yet again though, CAMs are tame despite at least modest
convergence along a trough and the nose of an 850 mb jet in
eastern OH/western PA but rather favoring development later on
across the ridges and quickly out of our area. If nothing
develops ahead of the dry air intrusion, then our precipitation
chances will rapidly cut off by late afternoon. Nevertheless,
SPC has maintained a larger area of a Marginal Risk (1/5) and a
Slight Risk (2/5) that only covers Forest and Venango Counties.
&&
.LONG TERM /FRIDAY THROUGH TUESDAY/...
KEY MESSAGES:
- Temperatures rebound to close out the week with scattered showers.
- More active pattern may return by late weekend.
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After Beryl's departure, ensembles linger the remnant upper trough
across the Great Lakes into Thursday while ridging off the East
Coast tries to nudge westward. Moisture and troughing may result in
continued shower chances into Thursday, especially in the ridges.
It's not until Friday into Saturday that the consensus is for the
trough to begin to shift out of the area, but this remains on the
lower confidence side and some showers may still linger especially
in the eastern half of the area. Temperatures are favored to rebound
back to or a few degrees above normal to close out the week into
next weekend. By the beginning of next week, a northwest flow sets
up over the area with a couple of disturbances set to impact the
forecast area. Machine learning is hitting a large portion of the
Plains, Mid-Atlantic, and Northeast for severe weather potential
starting Sunday, but will have to wait for details to iron out
better in the coming days. Slight chance PoPs have been introduced
but confidence is low.
&&
.AVIATION /06Z WEDNESDAY THROUGH SUNDAY/...
VFR is expected to prevail for most this TAF period. Since the
last update, a few showers and thunderstorms developed and
tracked north across eastern and central OH. This activity has
already lifted to the north. Into tomorrow morning, dry
slotting has been more favored. This will discourage further
precipitation development, save FKL with the best moisture along
the cold front. Dry slotting may also allow for a deeper mixed
layer, with daytime gusts up to 30kts favored with 50% to 60%
confidence during the day, save FKL and DUJ where chances are
closer to the 25% to 35% range.
Any precipitation that does develop will be scattered at best
and most terminals only need a VCTS / VCSH mention. The only
exception will be FKL and DUJ where some activity can develop
along the front.
Tomorrow night, winds will gradually subside as surface
profiles gradually stabilize, though an enhanced gradient may
keep sustained winds up overnight. Saturated northwest flow may
lead to some drizzle and low cloud development throughout the
overnight hours.
.Outlook...
Residual showers on the backside of the general trough system
may also linger into Thursday morning for eastern OH/northwest
PA. Restriction potential increases during that time, with
probabilities for MVFR cigs peaking around sunrise Thursday
(09-15Z) at 70-85% near/north of the PIT area and 50-70%
farther south. Ensembles favor VFR returning to the area
Thursday afternoon and staying in place thereafter.
&&
.PBZ WATCHES/WARNINGS/ADVISORIES...
PA...None.
OH...None.
WV...None.
&&
$$
SYNOPSIS...MLB
NEAR TERM...MLB/Shallenberger
SHORT TERM...MLB/Shallenberger
LONG TERM...MLB/Shallenberger
AVIATION...Milcarek/Shallenberger
Source:
PBZ issues Area Forecast Discussion (AFD) at Jul 10, 1:45 AM EDT---------------
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