PBZ issues Area Forecast Discussion (AFD) at Jul 31, 12:33 PM EDT157
FXUS61 KPBZ 311633
AFDPBZ
Area Forecast Discussion
National Weather Service Pittsburgh PA
1233 PM EDT Wed Jul 31 2024
.SYNOPSIS...
After a relative lull in activity today, shower and thunderstorms
will be possible through Saturday. A heavy rainfall threat exists
each day, along with a marginal chance for strong to severe
storms.
&&
.NEAR TERM /THROUGH TONIGHT/...
KEY MESSAGES:
- Convection should be largely suppressed during the day under
increased subsidence, but isolated instances are still
possible.
- SPCs Marginal Risk (1/5) has been maintained for damaging
wind.
- Continued well above normal temperature today.
-------------------------------------------------------------------
No midday updates needed as the forecast is in good shape...
Shortwave ridging evident in latest WV imagery will transition
over the area over the course of the day and result in a
relative lull in convective activity while also introducing more
mid-level dry air than we've seen the past couple days. A 20dm
increase in h500 heights along with h850 temperatures near 20C
this afternoon should result in daytime highs approaching 90F.
Today features less cloud cover across our area than the
previous two days and a couple degrees warmer than we were 24
hours ago. This has allowed for efficient destabilization with
latest mesoanalysis depicting 1000-1500 J/kg MLCAPE as
temperatures have risen to the mid 80s with dew points near 70.
Deep layer shear is also a bit better up to 25 knots across
southern Ohio with slightly more amplified flow aloft. So, we
have a better environment to work with today that poses a
conditional damaging wind threat. But, it's dependent on
whether or not we get storms to form in the first place to use
that environment which is low probability as ensemble chance for
measurable precip through 6pm is 10% or less. Latest CAMs are
not interested much at all which is most likely how today will
pan out given localized subsidence suppressing vertical growth
and lack of a defined lifting mechanism, but can't rule out
some isolated development especially later this evening with
another remnant cluster of storms diving through the Ohio Valley
with highest chances for Pittsburgh south and west. SPC has
maintained the Marginal Risk for severe weather today.
&&
.SHORT TERM /THURSDAY THROUGH THURSDAY NIGHT/...
KEY MESSAGES:
- Unsettled pattern continues, but low confidence in details.
- Potential severe risk continues with Marginal Risk (1/5).
-------------------------------------------------------------------
Details remain fuzzy and dependent on upstream convective
evolution, but latest hi-res CAMs do show the potential for MCS
(associated with convection currently developing over Iowa)
possibly impacting southern portions of the forecast later in
the evening as it propagates within the overall northwesterly
flow. Given the unfavorable timing for our neck of the woods,
chances are any organized convection should be weakening. Latest
mean NBM CAPE values are <500 by the evening across the region.
Machine learning does indicate a conditional wind potential, and
the Marginal Risk (1/5) for severe has been maintained across
the entire area covering the threat for damaging wind.
Thursday presents similar uncertainty as another shortwave
dives through the Great Lakes with a MCS again tracking near
the area. Machine learning and available guidance favor another
south and west track following the best progged instability
axis. A conditional damaging wind threat is in play with any
storms that develop on Thursday in our area in a similar
environment to today, but confidence remains low.
&&
.LONG TERM /FRIDAY THROUGH TUESDAY/...
KEY MESSAGES:
- Slower upper trough will maintain periodic precipitation chances
into the weekend.
- Temperatures dip back closer to normal.
-------------------------------------------------------------------
A slower moving, deeper trough then approaches on Friday with higher
confidence amongst the ensembles and while finer-scale details
remain uncertain, guidance suggests minimal environmental changes
beyond a slight uptick in area cloud cover and moisture resulting in
greater precipitation chances and more seasonable temperature.
Surface ridging and weak subsidence aloft behind the exiting trough
suggests a lower chance of rain on Sunday as temperature climbs a
few degrees above the daily average. Dry conditions may be short-
lived as the region will then remain positioned underneath northwest
flow while ridging persists across the Rockies. This pattern would
favor above normal temperature and periodic thunderstorm chances
fueled by weak shortwave movement.
&&
.AVIATION /18Z WEDNESDAY THROUGH MONDAY/...
LIFR stratus at KFKL and KDUJ should diminish in next hour or
so as dry advection and subsidence will continue.
Water vapor imagery and RAP analysis at 500 mb indicates that
weak upper trough is overhead and will be moving away this
afternoon, which will limit afternoon thunderstorm potential.
Diurnal heating will generate a scattered CU field as surface
pressure gradients favor west winds that could occasionally gust
to 20kts.
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...
Additional shortwave movement and a slow progressing upper level
trough will promote periodic shower and thunderstorm chances
through most of the weekend. Convective evolution will play a
significant role in the degree of cig/vis restriction
development throughout the week.
&&
.PBZ WATCHES/WARNINGS/ADVISORIES...
PA...None.
OH...None.
WV...None.
&&
$$
SYNOPSIS...88
NEAR TERM...MLB/88
SHORT TERM...88
LONG TERM...88
AVIATION...Craven
Source:
PBZ issues Area Forecast Discussion (AFD) at Jul 31, 12:33 PM EDT---------------
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