PBZ issues Area Forecast Discussion (AFD) at Aug 2, 12:45 PM EDT024
FXUS61 KPBZ 021645
AFDPBZ
Area Forecast Discussion
National Weather Service Pittsburgh PA
1245 PM EDT Fri Aug 2 2024
.SYNOPSIS...
Showers and thunderstorms will continue at times through
Saturday as a slow moving trough of low pressure crosses the
region. Some of the storms could contain locally heavy rainfall
and gusty wind. Mainly dry weather returns Sunday.
&&
.NEAR TERM /THROUGH TONIGHT/...
KEY MESSAGES:
- Scattered showers and thunderstorms this afternoon, some with
gusty wind and locally heavy rainfall possible.
- Cooler temperatures with increased cloud cover.
-------------------------------------------------------------------
The MCV has traversed the area and has mostly departed the region
early this afternoon. Subsidence following behind the remnant
MCV has been the predominant factor in inhibiting further
convection during the late morning through early afternoon. The
remaining cloud coverage will also limit destabilization and
weak flow aloft won't provide mush deep layer shear as Hi-Res
ensemble probability of >1000 J/kg of CAPE and >20 kts of shear
is around 50 to 60 percent. Storms or showers that do develop
will most likely be a result of lake breeze convergence and weak
shortwave energy in diffluent flow aloft resulting in scattered
coverage with highest probability in eastern Ohio.
Locally heavy rain is possible this afternoon as well, though any
flood potential would likely be due to training and especially in
urban areas that saw rain this morning. The Storm Prediction
Center has trimmed the Marginal Risk (1/5) south of I-70 with
damaging wind remaining the primary hazard with drier mid level
air in place. Will continue to mention these potential impacts
in the Hazardous Weather Outlook.
Overall coverage will wane after sunset with loss of
instability, but some CAMs keep showers around through the
overnight hours with ensemble probability highest in western PA,
coincidentally where the most rain fell within the last 24
hours. Will have to monitor for localized flooding concerns if
this solution comes to fruition through the overnight hours
tonight especially with a very juicy environment (>1.7" PWATs)
still in place.
&&
.SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/...
KEY MESSAGES:
- Scattered showers and thunderstorms continue tonight
- Periodic showers and thunderstorms continue Saturday
- Mainly dry Sunday, outside of the higher terrain areas
-------------------------------------------------------------------
The next, stronger shortwave trough will slowly approach the
Upper Ohio Valley region tonight. Scattered showers and
thunderstorms are expected to continue, though instability
should wane overnight. HREF output indicates a MU CAPE around
500 j/kg overnight tonight. Any severe potential should quickly
diminish this evening.
The trough will then slowly cross the Upper Ohio Valley region
on Saturday, with more widespread showers and thunderstorms
expected. The greatest coverage should be in the afternoon with
diurnal instability. Locally heavy rainfall will also remain
possible on Saturday.
The trough axis is expected to be across the Laurel Highlands
and the WV higher terrain by Sunday morning. While dry weather
is expected to the west of the trough, shower and thunderstorm
chances will continue especially for the higher terrain areas of
WV until the trough exits Sunday night.
Temperatures are expected to average above seasonable levels,
especially on Sunday as highs return to the mid 80s to near 90.
&&
.LONG TERM /MONDAY THROUGH FRIDAY/...
KEY MESSAGES:
- Shower and thunderstorm chances Tuesday
- Mainly dry for the remainder of the period
-------------------------------------------------------------------
Model ensembles indicate the Upper Ohio Valley region will be
under a broad upper trough from the early to middle part of the
week. A shortwave embedded in the trough will result in shower
and thunderstorm chances Tuesday into early Wednesday as it
crosses the region. Otherwise, surface high pressure should
maintain mainly dry weather through the long term period.
Temperatures are expected to be above average to start the week,
returning to more seasonable levels by mid week.
&&
.AVIATION /18Z FRIDAY THROUGH WEDNESDAY/...
Medium confidence forecast of 60%-70% as timing and placement
of showers and storms through this evening and development
/possibly/ of low clouds or fog overnight.
CAMS continue to support isolated to scattered showers and
storms this afternoon. Best placement and agreement resides in
eastern Ohio and northern West Virginia through 3Z. Given lack
of organization did not go with prevailing or tempo, but continued
to keep vicinity in forecast. There will be a lull in precip
overnight into Saturday morning, but a chance does exist for a
shower or storm overnight.
The other question will be fog development. HREF and NBM
visibility probs of less than 3SM are highest /30-40%/ along
and north of I80, while the percentages are about 20% higher
across the board for vis between 3-5SM. The statistical guidance
is even lower with IFR at DUJ and FKL. Will side with MVFR VIS
for now and see how things go and if a consensus develops they
can be nudged lower in future issuance. CIGS are a different
story where better agreement and slightly higher probs of CIGS
1KFT or lower, so will tether on the cusp of IFR for now and
hint at those conditions.
Any low clouds will be slow to lift Saturday morning, but most
sites will stay IFR/MVFR through the morning hours and likely
MVFR through the afternoon given the passage of an upper air
system. Showers and storms will be most numerous midday on
across western PA and northern West Virginia.
Wind will be light around five knots through the duration of the
forecast.
.Outlook...
Showers and thunderstorms with an upper level system will bring
brief sub VFR restrictions Saturday. IFR vis is possible if an
airport gets impacted by a stronger storm. VFR weather returns
after any morning fog Sunday through most of Tuesday.
&&
.PBZ WATCHES/WARNINGS/ADVISORIES...
PA...None.
OH...None.
WV...None.
&&
$$
SYNOPSIS...WM
NEAR TERM...WM/MLB/MAM
SHORT TERM...WM
LONG TERM...WM
AVIATION...McMullen
Source:
PBZ issues Area Forecast Discussion (AFD) at Aug 2, 12:45 PM EDT---------------
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