429
FXUS61 KPBZ 141810
AFDPBZ

Area Forecast Discussion
National Weather Service Pittsburgh PA
210 PM EDT Sun Jul 14 2024

.SYNOPSIS...
A more active weather pattern featuring increased thunderstorm
chances and the potential for severe weather will ensue later
this afternoon and continue through Wednesday, along with
continued heat and humidity. Dry and seasonable weather returns
by Thursday behind a cold front.

&&

.NEAR TERM /THROUGH TONIGHT/...
KEY MESSAGES:

- Potential for at least scattered thunderstorms presenting a
  damaging wind threat into the evening, mainly west of
  Pittsburgh.
- A late-night convective complex is possible as well, with
  another risk for isolated damaging wind.
-------------------------------------------------------------------

Quiet weather earlier today will be a memory soon, as we head
towards a period of active weather that will continue into
midweek.

First cluster of showers, just arriving into the northwestern
CWA, is the remnant of an earlier MCS. Most CAMs insist that
this will fade over the next few hours, and have some low PoPs
in the western CWA to handle this. Will watch developing
convection to the northeast of CLE on the lake shore as well.

Next concern is the MCS currently diving across Indiana towards
western Ohio. Many of the CAMs did not initialize well this
morning and thus likely don`t handle this complex correctly.
HRRR and RAP runs insist that these storms will largely fade as
they move across Ohio, ostensibly due to them approaching what
these CAMs assume will be a more hostile convective environment.
The RAP-based SPC mesoanalysis progs show a notable dropoff in
SBCAPE/MLCAPE this afternoon, likely due to reducing surface
dewpoints through dry air mixdown. Wonder if this is being
overdone a bit, and that there might be a bit more favorable
environment for storms during the late afternoon/early evening.
Keeping some chance PoPs mainly to the west of Pittsburgh for
now, highest in the ZZV vicinity, and will continue to monitor
trends. There is certainly potential for strong to isolated
damaging gusts with these storms. Cannot rule out the need for a
Severe Thunderstorm Watch for a few of our southwestern
counties.

The loss of daytime heating then may lead to a relative lull
during the late evening/early overnight period. Models still
point to convection arriving towards Monday morning ahead of a
shortwave reaching the eastern Great Lakes. Surface dewpoint
recovery and improving lapse rates aloft could lead to a
improvement of CAPE overnight, and, assuming storms can congeal,
a possible wind threat if instability does not become too
elevated.

&&

.SHORT TERM /MONDAY THROUGH WEDNESDAY NIGHT/...
KEY MESSAGES:

- Active weather with several convective rounds presenting
  potential severe hazards until the passage of a cold front on
  Wednesday.

- Heat risks are present Monday/Tuesday but will be dependent
  on convective evolution and resultant cloud cover.

-------------------------------------------------------------------

Convection may be ongoing at 12Z Monday, as whatever complex/MCS
can form continues to cross the region. Decaying
convection/lingering clouds could lead to a less favorable
environment for convection into Monday afternoon at least from
Pittsburgh on east. Clearing may be a bit more likely in eastern
Ohio by the afternoon hours, which could allow sufficient
destabilization for a fresh round of storms, paired with another
mid-level shortwave. CAPE on the order of 1000-2000 J/kg is
possible by afternoon, perhaps even higher in Ohio, with weak
shear and sufficient DCAPE to support mainly a damaging wind
threat and a secondary large hail threat where CAPE is more
favorably accumulated in the -10C to -30C hail growth zone. CSU
machine-learning guidance generally agrees with this. The
overall tornado threat appears low given the low shear, although
QLCS-type spinups could be a concern. There is also still some
potential for a more robust MCS to arrive later Monday evening
as well, although the threat of concentrated wind damage should
be a bit less for the Upper Ohio Valley as compared to upstream
areas. Nevertheless, the areawide SPC marginal day 2 risk is
justified.

Uncertainty only increases from here. Further rounds of
convection are possible ahead of the eventual frontal passage
thanks to weak shortwave passages Tuesday and Wednesday. Again,
damaging wind continues to be the primary threat mode. A more
stout shortwave trough dropping into the Great Lakes on
Wednesday will finally help to push a cold front along for an
eventual Wednesday afternoon/night passage, bringing a more
concentrated precipitation area Wednesday, but then an end to
the convective threat behind it.

Of course, heat and humidity will continue to be part of the
story during the early part of the week. The potential for
advisory-level heat index values of 100 or more on Monday (and
Tuesday for that matter) will be highly dependent on convective
extent and timing. With 850mb temperatures expected to reach or
exceed 20C over a good portion of the region, a lack of cloud
cover could lead to sufficient sunshine to get surface
temperatures into the mid 90s for some on either day, leading
to the higher heat index values. However, more abundant cloud
cover could keep temperatures below 90 and therefore stunt the
heat impact. Due to this, will hold off on any heat-related
headlines for now, hoping that time and additional near-term
information will lead to increased clarity. More concentrated
clouds and precipitation on Wednesday should limit heating below
advisory thresholds.

&&

.LONG TERM /THURSDAY THROUGH SATURDAY/...
KEY MESSAGES:

- A drier and cooler pattern will ensue on Thursday and continue
  into next weekend.

-------------------------------------------------------------------

The cold front should complete its passage Thursday morning, perhaps
stalling over the Central Appalachians/Middle Ohio Valley, with
expanding high pressure across the Great Lakes and northeast
CONUS into next weekend. Drier weather and cooler temperatures,
perhaps falling a few degrees below normal, can be expected
through Friday night.

The shallow upper troughing in place Thursday and Friday may be
replaced by rising heights Saturday/Sunday in response to increased
troughing over the Central Plains. This could also bring moisture
back from the south, leading to increased diurnal precipitation
chances, mainly southeast of Pittsburgh. A warmup back to seasonable
temperatures can also be anticipated.

&&

.AVIATION /18Z SUNDAY THROUGH FRIDAY/...
Mainly VFR conditions are expected today under the continued
influence of high pressure. Expect a few/sct CU with diurnal
heating and potential for an occasional SW wind gust to 20kts.

Uncertainty continues with in regards to the evolution of an MCS
currently crossing out of IN into western OH. This system is
expected to dive southeastward across OH and possibly clip the
ZZV around around 21-22z. TEMPOs have been added to account for
this impact. Elsewhere, other than an isolated shower or two,
the area will remain dry through the evening.

Another decaying MCS may impact the area overnight, but again,
there is low confidence on this and models are handling the
setup very poorly. A fresh round of storms is also possible
Monday afternoon, but this will largely depend on the evolution
of the previous system.

Westerly winds will gust to near 20 kts Monday afternoon

.Outlook...
Periodic shortwave movement will lend to thunderstorm chances
through mid week, peaking Wednesday with the approach and
passage of a cold front. Timing and coverage will be difficult
to ascertain even a day out due to the strong impact of prior
days convective evolution.

High pressure is favored by Thursday and ensure another period
of VFR and dry weather.

&&

.PBZ WATCHES/WARNINGS/ADVISORIES...
PA...None.
OH...None.
WV...None.

&&

$$

SYNOPSIS...CL/88
NEAR TERM...CL
SHORT TERM...CL
LONG TERM...CL
AVIATION...Rackley/Frazier