PBZ issues Area Forecast Discussion (AFD) at Jul 8, 8:46 PM EDT578
FXUS61 KPBZ 090046
AFDPBZ
Area Forecast Discussion
National Weather Service Pittsburgh PA
846 PM EDT Mon Jul 8 2024
.SYNOPSIS...
Dry weather continues through most of Tuesday ahead of the
remnants of Hurricane Beryl that will bring showers and
thunderstorms to the area beginning Tuesday night. Tuesday and
Wednesday will be the hottest days of the week with heat indices
approaching 100 degrees.
&&
.NEAR TERM /UNTIL 6 AM TUESDAY MORNING/...
KEY MESSAGES:
- Dry with lows 5-10 degrees above average.
-------------------------------------------------------------------
No changes to the forecast were necessary for the evening
update. High pressure will maintain dry weather through
tonight, although high clouds will continue to stream across the
region as moisture is drawn northeastward well ahead of the
remnants of Hurricane Beryl. There is still a short window of
opportunity for a stray orographically driven shower in the
ridges, but development to this point has been off to our east,
where it is largely expected to remain. Any remaining cumulus
will dissipate with sunset, and we'll be left with cirrus and a
light to calm wind overnight.
A warm and muggy night expected as southwest flow will continue to
usher in moisture and weak warm advection combined with the cloud
coverage will keep lows above normal in the upper 60s to low 70s in
the urban areas.
&&
.SHORT TERM /6 AM TUESDAY MORNING THROUGH TUESDAY NIGHT/...
KEY MESSAGES:
- Hot and humid Tuesday with heat indices nearing 100 degrees.
- Marginal Risk (1/5) for severe overnight Tuesday night in eastern
Ohio.
-------------------------------------------------------------------
Cirrus coverage will thicken ahead of the remnants of Beryl with
increasing moisture aloft in southwest flow. Said southwest flow
will also promote additional warm advection and hi res ensemble mean
850 mb temperatures climb up to 21C. Weak moisture advection
will keep dew points steady if not rising slightly through the
afternoon. This will result in heat indices climbing to near or
just touching 100 degrees, especially in the urban areas. The
warm, moist airmass will continue into Tuesday night providing
little relief with a 70-90% chance of lows >70F primarily south
of I-80. Should the cirrus coverage be thinner than currently
forecast, it's possible that Heat Advisory criteria may be
reached, but that is a lower probability solution. Regardless,
those who are sensitive to heat should take extra precautions
and remember to check on those who are at risk for heat
illnesses.
A Marginal Risk (1/5) for severe has been introduced for a small
sliver of our eastern Ohio counties as a warm front lifts north
through the Ohio Valley late Tuesday night. A few tornadoes would be
the primary threat; that said, the majority of forecast soundings
from the CAMs suggest a stable surface given the poor diurnal
timing. Dynamics won't be an issue as plenty of low level shear will
be present as Beryl gets closer, but the chance of a storm rooting
at the surface and subsequently posing a tornado threat is low
probability. Otherwise, we should see a limited severe threat with
mid level lapse rates not all that favorable and limited deep layer
instability as moisture increases through the depth of the
column.
&&
.LONG TERM /WEDNESDAY THROUGH MONDAY/...
KEY MESSAGES:
- Remnants of Beryl track near the area beginning on Wednesday.
- Still uncertainty with potential phasing with northern stream
trough which will determine potential for severe and flooding
concerns.
- Temperatures rebound to close out the week with scattered showers.
-------------------------------------------------------------------
The remnants of Beryl approach and impact the area starting on
Wednesday. Primary uncertainty at this point comes from how Beryl
phases with a northern stream trough. In terms of rainfall, a more
phased solution would result in longer residence time and a stronger
push of moisture providing amounts on the higher end of the wide
distribution. Less phasing and quicker movement would provide
less rainfall on the lower end of the distribution. Current NBM
probabilities for >1" over a 48 hour period are highest to our
west, north, and east (only ~30% at PIT) coincident with the
potential intrusion of a dry slot dependent on the phasing of
the low. Can't rule out some hydrology concerns as we sit with
uncertainty as the northern half of the area remains in a Slight
Risk (2/4) for excessive rainfall and the rest of the area in a
Marginal Risk (1/4). The driest solution could even potentially
raise heat concerns on Wednesday if it comes to fruition,
especially south and east of Pittsburgh, as moisture surges with dew
points into the mid 70s. This is well represented by the NBM
10th/90th percentile spreads in MaxTs on Wednesday sitting at
78/93 respectively.
For the severe threat, the track of the low again will play a big
role. The points of interest will be a warm front, how long the area
may remain in an open warm sector ahead of a cold front/surface
trough, and, dependent on the low track, what type of environment we
see. A possible severe risk could be focused along the warm front as
it moves north and/or the cold front later in the day, though all of
that will ultimately be dependent on the track of the low which, as
stated, is still uncertain. Ample shear looks to be available as the
CAMs now just start coming into play, so a solution with a more
moist environment with low LCLs would indicate the necessity to watch
for a tornado risk. The flip side would be a drier atmosphere -->
more insolation --> more instability supporting a conditional
wind/hail risk with diurnally driven convection. That said, a
potential failure mode here with the drier environment could be
an atmosphere that is simply too dry to convect in the first
place. SPC has maintained the Marginal Risk (1/5) covering
areas north of I-80. Still a good amount of questions remain as
we await better agreement amongst the ensembles and a higher
confidence forecast in which one will play out, but the array of
potential solutions is narrowing.
After Beryl's departure, ensembles linger the remnant upper trough
across the Great Lakes into Thursday while ridging off the East
Coast tries to nudge westward. Moisture and troughing may result in
continued shower chances into Thursday, especially in the ridges.
It's not until Friday into Saturday that the consensus is for the
trough to begin to shift out of the area, but this remains on the
lower confidence side and some showers may still linger especially
in the eastern half of the area. Temperatures are favored to
rebound back to or a few degrees above normal to close out the
week into next weekend.
&&
.AVIATION /01Z TUESDAY THROUGH SATURDAY/...
VFR prevail for the TAF period with high confidence. Calm to
light and variable winds will persist overnight. There is a
very low chance of fog tonight (less than 10%) confided to river
valley ports (FKL, HLG). Tomorrow, mixing will ensue and
contribute to scatted to broken high-based (6kft-8kft) cumulus
decks. Winds will accelerate and veer from south to west
throughout the day. In the late afternoon period (4pm-8pm),
there is a less than 15% chance of showers/storms in eastern
Ohio and northwest Pennsylvania. Cumulus will dissolve after
sunset and give way to mid-level broken decks as winds lighten
and veer northerly.
.Outlook...
There is a 30% to 40% chance cigs south of Pittsburgh drop to
MVFR in the 6am to 9am timeframe Wednesday morning with the
remnants of Beryl. Chances increase to 50% to 70% north of
Pittsburgh with rain/storms more likely.
&&
.PBZ WATCHES/WARNINGS/ADVISORIES...
PA...None.
OH...None.
WV...None.
&&
$$
SYNOPSIS...MLB
NEAR TERM...MLB/CL
SHORT TERM...MLB
LONG TERM...MLB
AVIATION...Milcarek
Source:
PBZ issues Area Forecast Discussion (AFD) at Jul 8, 8:46 PM EDT---------------
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