PBZ issues Area Forecast Discussion (AFD) at Jul 31, 6:06 PM EDT113
FXUS61 KPBZ 312206
AFDPBZ
Area Forecast Discussion
National Weather Service Pittsburgh PA
606 PM EDT Wed Jul 31 2024
.SYNOPSIS...
Showers and thunderstorms will be possible daily through the
weekend with the best chance coming Friday night. A heavy
rainfall threat exists each day along with a low end chance for
severe thunderstorms.
&&
.NEAR TERM /UNTIL 6 AM THURSDAY MORNING/...
KEY MESSAGES:
- Isolated convection expected through the evening hours.
- SPCs Marginal Risk (1/5) has been maintained for damaging wind.
- Continued well above normal temperature today.
-------------------------------------------------------------------
A few thunderstorms have managed to fire in eastern Ohio during
the late afternoon on outflow from an earlier MCS to the west.
While the convective parameters look promising for a downburst
threat, including 1000-1500 J/kg of MLCAPE, DCAPE of 1000-1300
J/kg, and relatively low shear, the storms have struggled to
push any appreciable reflectivity above 25kft to this point. The
dry air near and above this level is likely putting a lid on
these storms to some degree. The very shallow and dissipating
cumulus field over southwest PA/northern WV is further evidence
of this dry air. However, we are watching stronger activity
just to our northwest, in the CLE CWA, that might require
statements/warnings if they maintain strength. However, as
instability starts to fade with the setting sun, we expect most
of this activity to slowly weaken as we approach and pass
sunset. Coverage will remain at the isolated level through the
evening hours, and any late-night MCS activity is still figured
to remain mainly off to our southwest. Away from the storms, a
warm and muggy night is forecast.
&&
.SHORT TERM /6 AM THURSDAY MORNING THROUGH FRIDAY NIGHT/...
KEY MESSAGES:
- Another MCS dives to our southwest Thursday with a conditional
threat for damaging wind in our area.
- Better chance for rain Thursday night into Friday.
- Temperatures remain above average.
-------------------------------------------------------------------
The upper level pattern remains similar on Thursday with northwest
flow aloft prevailing, though ensemble 500 mb heights nudge upward
slightly through the day as shortwave ridging passes through in
between troughs to our west and east. At the surface, the remnants
of, you guessed it, another MCS will be following a similar track to
the previous couple days off to our south and west along the axis of
highest instability. A similar environment will be in place to
Wednesday with the best ensemble overlap of instability and shear
south and west of Pittsburgh. The question remains whether or not
storms develop. There is some better agreement in the models with
development to some extent across our area in the afternoon
perhaps aided by the lake breeze and remnant outflow from the
MCS. We will face another conditional damaging wind and heavy
rainfall threat with PWAT values up around 1.5".
A brief lull is favored shortly after sunset Thursday night, but
things may ramp up again in the overnight period. Ensemble clusters
exhibit good agreement in the speed and position of a deeper upper
low slowly moving through the Midwest overnight Thursday night. Flow
aloft will back southwesterly and draw in deeper layer moisture
again saturating the profile with PWAT values rising up to 1.7-1.9".
Unfavorable diurnal timing of a weak warm front should preclude much
of a severe threat in our neck of the woods, but heavy rain will
remain a possibility with weaker shear and tall CAPE profiles
favoring efficient rainfall producers. Plenty of moisture will
remain in place through the day on Friday in the warm sector to
support better rain chances than we've seen so far this week with
stronger upper diffluence as ensemble probability of measurable
precip increases to 60+% across most of the area. Severe
weather seems less likely with the thermal trough/upper level
colder air to our west and better dynamics favored outside of
our area on the south side of the upper low.
&&
.LONG TERM /SATURDAY THROUGH WEDNESDAY/...
KEY MESSAGES:
- Slower upper trough will maintain periodic precipitation chances
into the weekend.
- Temperatures dip back closer to normal.
-------------------------------------------------------------------
Ensemble clusters flatten out the upper low Saturday into Sunday as
it slides through and the surface low spins near Lake Erie.
While finer-scale details remain uncertain especially given the
lower predictability near and short term, rain chances are
favored to continue through the weekend until the upper trough
clears the area and drier weather is favored to start the next
work week. Some disagreement comes into view with the upper
level pattern in terms of depth of the trough by late weekend
and how fast heights begin to rise, but the consensus is that
the pattern turns slightly more zonal, though still in west-
northwest flow which would favor above normal temperature and
periodic thunderstorm chances fueled by weak shortwave movement.
&&
.AVIATION /22Z WEDNESDAY THROUGH MONDAY/...
Water vapor imagery and RAP analysis at 500 mb indicates that
weak upper trough has moved to the east of the area and
subsidence is shown when looking at the 400-250 mb Potential
Vorticity advection. This has limited any deep convective
development as expected.
Diurnal Cumulus field is extensive but relatively shallow and
despite 1,500-2,500 j/kg SBCAPE storms have not yet formed.
Stronger instability over southern Indiana extends into SW Ohio
and will be available for eventual storms moving into area.
Rain chances increase overnight mainly over southwest half of
forecast area with potential for upstream MCS to develop in WNW
flow and brush the area. This would mainly be an issue for ZZV
and HLG and MGW TAF sites.
.Outlook...
An active pattern is expected to continue to promote almost
daily chances of thunderstorms. Rather high chance Thursday
evening and again Friday and Saturday as a slow moving upper low
crosses the area. Ceiling and visibility restrictions will be
limited to thunderstorm clusters for the most part, but
probabilities will increase Friday and Saturday with weaker flow
and increased probability of showers and thunderstorms.
&&
.PBZ WATCHES/WARNINGS/ADVISORIES...
PA...None.
OH...None.
WV...None.
&&
$$
SYNOPSIS...MLB
NEAR TERM...MLB/CL
SHORT TERM...MLB
LONG TERM...MLB
AVIATION...Craven
Source:
PBZ issues Area Forecast Discussion (AFD) at Jul 31, 6:06 PM EDT---------------
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