029
FXUS61 KPBZ 121155
AFDPBZ

Area Forecast Discussion
National Weather Service Pittsburgh PA
755 AM EDT Fri Jul 12 2024

.SYNOPSIS...
Rising temperature is expected today through early next week
before a late week cold front returns seasonable temperature to
the area. Confidence is growing for an active weather pattern
featuring severe potential beginning Sunday afternoon and
peaking Tuesday into Wednesday morning.

&&

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

- River Valley fog focused in northwest PA will dissipate this
  morning but potentially return tonight.

- Afternoon high temperature will be approximately 5 degrees
  above the daily average.
-------------------------------------------------------------------

Despite patches of lingering stratus clouds, areas of fog
focused in river valleys has developed mainly in northwest PA.
Additional fog may develop farther south within river valleys as
peak cooling occurs, with all fog dissipating shortly after
sunrise with heating/mixing.

Weak warm advection within southwesterly flow will support a
return to above normal temperature this afternoon as the region
sits east of a saggy western Great Lakes trough. Most locations
will be dry but isolated convection entering eastern Ohio zones
can`t be ruled out as the trough lifts east, but limited column
moisture will keep probabilities low. Additional, surface
convergence along the WV higher terrain due to a Carolina
coastal low may combine with diurnal heating for isolated
afternoon showers/storms. Again, probabilities are low with
convection quickly moving east of the region in conjunction with
storm layer wind to the NE.

Little environmental change to the overnight period should
result in patchy river valley fog formation. The biggest
limiting factor will be any lingering mid-level clouds
associated with the passage of the upper trough axis.

&&

.SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/...
KEY MESSAGES:

- Increasing heat risk expected as temperatures sit 5 to 10
  degrees above the daily average.

- Low probability thunderstorms possible as a period of a more
  active pattern begins.

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

Broad zonal flow with rising heights aloft will support a
continuation of rising temperature Saturday, with highs expected
to sit 5 to 10 degrees above the daily average. Little to no
forcing and warm air aloft should ensure dry weather, but a few
convective models hint at enough heating to destabilize the
environment (generating ~1000 J/kg SBCAPE) for an isolated
thunderstorm. The most likely form of lift will be a lake breeze
off Lake Erie providing enough convergence for an isolated
shower/thunderstorm. Forecast maintains dry condition based on
ensemble means, but trended toward isolated mentioning for
northwest PA to capture this conditional outcome.

The first in a series of upper level shortwaves dropping
southeast over the Rockies ridge will approach the Upper Ohio
River Valley Sunday. Its depth and southeast movement/timing
will be influenced by convective evolution of likely MCS
development beginning in the Upper Midwest. The favored solution
at this time has either convective development and continuation
of a weakened MCS starting early Sunday afternoon. Lack of
notable moisture prior to its arrival and residual warm air
aloft will likely keep severe probabilities low, but enough
instability from sfc heating (highs will be 5-10 degrees above
normal) should lead to scattered thunderstorms coverage. More
notably, this shortwave is likely to serve as the primer for a
more active weather pattern the following days.

&&

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

- An active severe weather pattern is anticipated through
  Wednesday morning, which will subside thereafter.

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

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

The basic synoptic pattern evolution will feature a series of
shortwaves dropping out of the upper Central Plains through the
Great Lakes region Monday through Wednesday and usher a
transition to broad upper troughing over the northeast CONUS to
end the week. Repositioning of the surface high initially SE
is likely to foster a hot, humid environment for the Upper Ohio
River Valley thanks to warm, moist southwest surface flow. The
combination of the hot/humid environment and upper shortwaves
will lead to increase thunderstorm chances that historically
see higher probabilities for severe weather. Deterministic
and AI-driven models confirm this pattern recognition by
portraying MCS movement through or near the region
Monday/Tuesday before the surface cold front passes Wednesday.
Spread and variations in the outcomes remain high as a given
day`s environment will be predicated on prior convective
evolution; but enough signal is present to alert for the
potential for multiple rounds of severe weather.

Prior to the cold front passage Wednesday, the hot and humid
environment may also lead to notable heat risks for the region
as air temperatures on Monday/Tuesday approach the mid 90s and
heat indices cross the 100 degree Heat Advisory threshold.
The main limiting factor is potential for thunderstorms to
shut-off daytime heating and/or provide excessive cloud cover
that stunts surface warming.

Ensembles favor the cold front passing Wednesday, but spread
exists in the shape of the upper trough and how quickly
drier/cooler conditions return for all locations. Most locations
should experience dry and seasonable weather Thursday, but storm
chances may linger in southern zones if the front ends of
stalling south.

&&

.AVIATION /12Z FRIDAY THROUGH TUESDAY/...
Morning fog mostly confined to river valleys should dissipate by
13Z with the onset of daytime heating and mixing. VFR conditions
and light winds prevail thereafter through much of the TAF
period. Hi-res models are split on whether there will be enough
boundary layer moisture for a fair weather cu field to develop
this afternoon. Even if it does form, coverage would be few/sct
and cigs around 5kft, resulting in little to no impacts.

Ensembles are showing fog potential returning early Saturday
morning (similar to this morning), with probabilities topping
out around 40-50% for visibilities below MVFR along and adjecent
to river valleys from roughly 09Z-13Z.

.Outlook...
Ensembles favor VFR prevailing through the weekend outside of
overnight/early morning patchy fog.

&&

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

&&

$$

SYNOPSIS...Frazier/Shallenberger
NEAR TERM...Frazier
SHORT TERM...Frazier
LONG TERM...Frazier
AVIATION...Cermak