PBZ issues Area Forecast Discussion (AFD) at Jul 13, 7:41 AM EDT795
FXUS61 KPBZ 131141
AFDPBZ
Area Forecast Discussion
National Weather Service Pittsburgh PA
741 AM EDT Sat Jul 13 2024
.SYNOPSIS...
A more active weather pattern featuring increased thunderstorm
chances and the potential for severe weather is favored starting
Sunday evening through Wednesday. Heat risks will remain
elevated during this period as well. Dry and seasonable weather
is likely late next week after the passage of a cold front.
&&
.NEAR TERM /THROUGH TONIGHT/...
KEY MESSAGES:
- Above normal temperature will continue with plenty of
insolation.
- Isolated afternoon convection can't be ruled out, but
probabilistically is unlikely today.
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7am Update - The forecast for today remains on track. Despite a
few convective speckles in the CAMs this afternoon, still think
the relatively dry column, weak shear/lapse rates, and notable
warm layer near 600mb will suppress any development this
afternoon. The HRRR is particularly (over) aggressive at mixing
out dewpoints into the lower 50s this afternoon, which would
certainly preclude any pop-up showers reaching the ground.
Previous Discussion...
Aside from subtle height rises, little has changed in the
synoptic environment today as a warm but relatively dry airmass
remains in place. Though diurnal heating will foster afternoon
cumulus, plenty of insolation will ensure another day with high
temperature in the upper 80s to lower 90s.
There remain hints of isolated afternoon convection by various
CAMs either along the WV higher terrain or near a potential Erie
lake breeze. Despite potential for near 1000 J/kg mean CAPE,
factors like the remaining presence of a notable warm layer near
600mb (see 00z sounding), lack of greater column moisture, and
weak shear/lapse rates all lend to too low of a probability of
occurrence for mention in the forecast. Any storm threat will
quickly end after the sun sets and the surface inversion
develops.
&&
.SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/...
KEY MESSAGES:
- Increasing heat risk expected as temperatures sit 5 to 10
degrees above the daily average.
- A more active pattern begins Sunday with a series of crossing
shortwaves and possible MCSs.
-------------------------------------------------------------------
Slight shifting of the surface ridge SE in response to shortwave
movement over the western Great Lakes will foster weak warm
advection into the Upper Ohio River Valley Sunday. This will
trend area temperature toward the lower to mid 90s and foster at
least a low probability for locations to be near 100 degrees for
heat indices. That shortwave movement will approach the region
late in the day and will be responsible for the encroachment of
an MCS from the northwest. Initial CAM analysis suggests the
prior warm air aloft and dry environment favors weakening of the
MCS, meaning Sunday night may either remain dry or just see
areas of light rain showers plus increased cloud cover.
Crucially, this first shortwave/decaying MCS is pegged by models
to help erode/cool the warm air aloft and serve to prime the
region for additional shortwave movement Monday. Ensembles are
trending toward higher probabilities for showers and
thunderstorms ahead of that wave Monday, but much variation
remains (and will be tethered, in part, to upstream convective
evolution). Current consensus favors an afternoon timing where
mean SBCAPE values will range from 2000-3000 J/kg, weak shear
and DCAPE values around 1000 J/kg; these components lend to a
damaging wind (and lower probability hail threat) via either
individual storm clusters or a secondary MCS. Timing and
presence of convection will also greatly determine the extent of
potential heat risks. The lack of convection and cloud cover
through a portion of the afternoon could foster mid 90s highs
with rising dewpoints creating fairly widespread heat indices
above 100F; early convection and/over lingering cloud cover may
make it difficult to even hit 90.
&&
.LONG TERM /TUESDAY THROUGH FRIDAY/...
KEY MESSAGES:
- Active weather with the potential for severe hazards remain
possible Tuesday into Wednesday until the passage of a cold
front.
- Heat risks could be maximized Tuesday, but will be dependent
on convective evolution and resultant cloud cover.
- Dry weather and seasonable temperature are likely to end the
work week.
-------------------------------------------------------------------
Ensembles favor additional shortwave movement south of a
deepening upper level trough north of the Great Lakes Tuesday
into Wednesday. The more well developed trough is then favored
to push a cold front through the region Wednesday
afternoon/evening and position broad upper troughing over the
Great Lakes to end the work week. In a broad sense, this pattern
lends to a peak in hot/humid conditions and potential severe
weather Tuesday; peak shower/thunderstorm chances Wednesday with
frontal passage; and dry weather with seasonable temperature
Thursday into Friday.
It remains hard to discern thunderstorm coverage, timing and
scope of potential severe threats as subtle variations in
shortwave positioning and potential weak ridging between waves
remains large among ensemble model solutions. And as has been
previously stated, prior days' convective evolution will have
significant influence on Tuesdays/Wednesdays outlooks. But
awareness of potential hazardous conditions remains a necessity
as there is a potential widespread damaging wind threat and/or
fairly widespread heat advisory day Tuesday. The best course of
action will be to continue to monitor the latest updates and see
what trends in model depictions suggest.
&&
.AVIATION /12Z SATURDAY THROUGH WEDNESDAY/...
Mainly VFR conditions are forecast over the next 24 hours as
high pressure remains in control. Patches of mid clouds this
morning will give way to scattered afternoon cumulus in daytime
mixing. An isolated shower cannot be totally ruled out, but
chances of impacting any TAF site are too low for inclusion.
Wind will remain generally light and variable.
.Outlook...
Ensembles favor VFR prevailing through Sunday outside of
overnight/early morning patchy fog. The likelihood of
restrictions with convection will increase Monday and Tuesday.
&&
.PBZ WATCHES/WARNINGS/ADVISORIES...
PA...None.
OH...None.
WV...None.
&&
$$
SYNOPSIS...Frazier
NEAR TERM...Rackley/Frazier
SHORT TERM...Frazier
LONG TERM...Frazier
AVIATION...CL/88
Source:
PBZ issues Area Forecast Discussion (AFD) at Jul 13, 7:41 AM EDT---------------
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