PBZ issues Area Forecast Discussion (AFD) at Aug 27, 8:09 AM EDT
738
FXUS61 KPBZ 271209
AFDPBZ
Area Forecast Discussion
National Weather Service Pittsburgh PA
809 AM EDT Tue Aug 27 2024
.SYNOPSIS...
Hot and humid today and Wednesday. Strong to severe storms
could develop Wednesday afternoon. Conditions will remain warm,
muggy and unsettled through the end of the week.
&&
.NEAR TERM /UNTIL 6 PM THIS EVENING/...
KEY MESSAGES:
- Hot, humid and mainly dry weather today.
- Heat indices in the mid to upper 90s for much of the region.
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Slow height rises expected today as a large ridge builds into
the midwest. With plenty of sunshine, and warm air advection,
high temperatures will push into the 90s for much of the
forecast area. For most of Ohio, northern WV and Southwest PA,
NBM probs of max T>90 range from 90 to 100%. Further north in
western PA, probs max T >90 fall off to 50 to 80% with
locations north of I-80 seeing low probs for temps greater than
90. Probs of max T > 95 really fall off with portions of Ohio
ranging close to 50 to 60%, while most of northern WV and W PA
are showing probs less than 30%. Heat indices will be quite
toasty as well with surface dewpoints in the 60s to low 70s for
much of the day. We may see dewpoints decrease a bit later this
afternoon as mixing increases and begins to bring drier air down
to the surface. Heat indices look to remain below advisory
levels with low to upper 90s possible this afternoon.
With the building ridge, and lack of much forcing, NBM probs
for measurable rainfall are less than 5%. Some of the
deterministic models want to try and bring a late day shortwave
over top of the ridge and drive it southward. This feature looks
rather weak and will be fighting the amplifying ridge.
&&
.SHORT TERM /6 PM THIS EVENING THROUGH THURSDAY/...
KEY MESSAGES:
- There is a slight risk for severe storms on Wednesday, with
showers and thunderstorms expected mainly in the afternoon and
evening.
- Well-above normal temperature continues, with heat indices
near 100F in some areas.
- Temperatures remain well above normal Thursday with a
continued threat for convection.
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High uncertainty on the convection threat and high temperatures
on Wednesday. This will also have an impact on the heat indices
as well. Differing model solutions on shortwave/surface cold
front impact Wednesday afternoon. This would have an effect on
the strength of the ridge, cloud cover, precipitation
initiation and timing, and ultimately the high temperatures.
Ensembles are showing a series of shortwaves moving over top of
the ridge and flattening it tonight and Wednesday. At the same
time, a weak surface cold front is shoved southward as heights
fall. None of the large scale ascension is very strong on
Wednesday, as the main shortwave looks to remain well to the
west of the area. However, with the cold front crossing, this
would likely spark showers and storms as it does so. Current NBM
probs are not high for measurable rainfall and thunder,
generally less than 40%, but this would be a place to lean on
the CAMs to pick up on the more mesoscale features. Instability
will increase on Wednesday, but current CAMs are keeping the most
buoyant air to our west and to our east. Wind shear will also
increase, with 20 to 25kts anticipated as the front crosses.
Limiting factors for stronger convection on Wednesday will be
the very warm air aloft and increasing cloud cover as the ridge
breaks down and the front pushes through. Current NBM highs and
surface dewpoints look a little over done considering the setup.
Will back of to closer to the 25th percentile to cover these
features.
A slight risk (2/5) for severe storms remain on Wednesday, with
the primary threat being damaging wind.
Another minor and brief amplification of the ridge is possible
on Thursday. The cold front, that should cross the region on
Wednesday, will likely stall somewhere over the Mid-Atlantic
region and sit there through most of the day. Another shortwave
will cross the area Thursday afternoon keeping in the risk for
showers and storms.
&&
.LONG TERM /THURSDAY NIGHT THROUGH MONDAY/...
KEY MESSAGES:
- Temperatures remain well above normal through Friday.
- Temperatures will cool a bit over the weekend, with an
increasing threat of showers and storms Friday into Saturday.
- Dry weather looks to return for the end of the long term
period.
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Ensembles indicate amplifying central-CONUS ridging by late
week, renewing northwest flow over the area and bringing some
relief from the heat. A more potent cold front is progged early
weekend, which may return more widespread rain chances to the
area.
&&
.AVIATION /12Z TUESDAY THROUGH SATURDAY/...
VFR is expected today as upper level ridging builds in. A
leftover mid-level cloud deck from yesterday's convection over
the Great Lakes is overspreading the area from the northwest
this morning, bringing pockets of bkn/ovc cigs around 7-10kft.
This should move out of the area through the morning, giving way
to a scattered cu layer this afternoon with cigs closer to
5kft. There could be an isolated afternoon thunderstorm near
FKL and DUJ as a weak shortwave crosses on the northern
periphery of the ridge. However, low confidence in occurrence
and isolated coverage preclude mention of thunder in the TAFs.
VFR likely prevails overnight, but convective models are
beginning to suggest a round of thunderstorms approaches from
the northwest during pre-dawn hours before dissipating after
sunrise as they enter the local area. This could bring impacts
primarily to FKL and possibly DUJ in the 08Z-12Z timeframe if it
does occur, but once again confidence is too low for mention in
the TAF at this time.
.Outlook...
Periodic restrictions in scattered showers and thunderstorms
are possible Wednesday through Saturday with a series of
crossing disturbances.
&&
.PBZ WATCHES/WARNINGS/ADVISORIES...
PA...None.
OH...None.
WV...None.
&&
$$
SYNOPSIS...22
NEAR TERM...22
SHORT TERM...22
LONG TERM...Rackley
AVIATION...Cermak/WM
Source: PBZ issues Area Forecast Discussion (AFD) at Aug 27, 8:09 AM EDT (https://mesonet.agron.iastate.edu/p.php?pid=202408271209-KPBZ-FXUS61-AFDPBZ)
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