PBZ issues Area Forecast Discussion (AFD) at Aug 29, 6:59 PM EDT064
FXUS61 KPBZ 292259 AAB
AFDPBZ
Area Forecast Discussion...UPDATED
National Weather Service Pittsburgh PA
659 PM EDT Thu Aug 29 2024
.SYNOPSIS...
Hot and humid conditions will persist through Saturday with
scattered afternoon convection favoring the eastern higher
terrain. Widespread precipitation is likely Saturday into early
Sunday morning ahead of a cold front. Dry and more seasonable
weather is expected thereafter.
&&
.NEAR TERM /THROUGH FRIDAY/...
KEY MESSAGES:
- Widespread heat indices in the lower to mid 90s likely.
- Scattered afternoon and evening storms possible, mainly south
and east of PIT, with a low probability for a wind threat.
----------------------------------------------------------------
500mb ridging to the west with weak, very discrete shortwave
movement in the lower levels will combine with the hot, humid
airmass to generate scattered afternoon to early evening
thunderstorms. Latest analysis shows surface
heating/destabilization favoring locals mainly south of
Pittsburgh with up to 3000 J/kg CAPE along with weak sfc
troughing along the eastern ridge line. This should favor these
two areas through the evening while the rest of the region may
only see isolated development.
Strong instability, 90th percentile PWAT values and slow storm
motion increases risk for localized flash flooding, though weak
lapse rates and forcing should limit convective maintenance to
sit on any one location for too long. Any severe threat will be
tied to precip loading in storms resulting in wet microbursts,
but the same limiters for flash flooding apply here as well.
Convective evolution is expected to move east of the region
through this evening, though strong enough convective outflows
could prolong storm duration in western PA.
Beyond dwindling convective activity, this evening will also see
loss of sunshine that will aid reduction of heat concerns. Much
of the region is likely to hold current heat index values
(around 90-95 degrees) through 6pm.
&&
.SHORT TERM /FRIDAY NIGHT THROUGH SATURDAY NIGHT/...
KEY MESSAGES:
- Temperatures remain well above normal Friday with potential
for isolated afternoon thunderstorms.
- Widespread convection likely Saturday with a low probability
wind threat.
-------------------------------------------------------------------
The ridge axis will shift over the upper Ohio River Valley
Friday in response to an upper level trough dropping towards the
upper Mississippi River Valley. Most of the region is likely to
remain dry and continue to deal with above normal temperature,
with heat indices well into the 90s. However, ensembles suggest
that the combination of weak shortwave movement ahead of the
approaching trough and enough diurnal heating could foster
isolated afternoon thunderstorms for portions of eastern OH into
northwest PA.
There is high confidence in the upper trough approach by
Saturday, though the upper jet will lag behind the initial
trough wave. This means the cold front may remain farther to the
NW, but ensembles remain bullish in enough convergence along a
pre-frontal trough to support fairly widespread line of
convection that will track SE through the day. A low probability
for damaging wind exists with these storms, but that will likely
be tethered to maximizing heating/destabilization ahead of the
boundary to boost CAPE values. Latest ensemble analysis is
fairly bearish on this outcome (more likely that mid-level moist
advection introduces enough cloud cover to limit degree of
heating). High PWAT values will remain and keep a minima of
flash flood potential, but forward motion should preclude any
issues.
&&
.LONG TERM /SUNDAY THROUGH THURSDAY/...
KEY MESSAGES:
- Cold frontal passage favored for Sunday with low probability
storms ahead of that boundary.
- High likelihood for another prolonged dry and seasonable
weather pattern.
-------------------------------------------------------------------
There is fairly high confidence in jet streak passage associated
with the actual trough axis late Saturday into Sunday morning.
This will push the surface cold front through the region,
tapping into residual moisture to produce lower probability
showers and thunderstorms ahead of the boundary.
By Sunday night, dry weather will develop as high pressure
builds into the region. Long range patterns favor a continuation
of Rocky ridging and broad East Coast troughing, promoting a
prolonged period of dry weather with seasonable temperature
(initially cooler Monday/Tuesday before height rises result in
above normal temperature toward the end of the week). Variations
in this pattern are likely subtle and dependent on the timing
and strength in the shortwave movement in NW flow.
&&
.AVIATION /00Z FRIDAY THROUGH TUESDAY/...
VFR generally prevails overnight, though some potential for
fog exists overnight for FKL/DUJ as well as any areas that
experienced rain this afternoon.
Another daytime cu field is expected and chances for showers
and thunderstorms return towards the tail end of the current TAF
period on Fri, especially along and west of a line from ZZV-
PIT-FKL. Prob30 comments were included Fri afternoon in the TAFs
for terminals in that zone.
.Outlook...
Restrictions are possible in scattered showers and thunderstorms
both Friday and Saturday as a cold front approaches and crosses
the area. VFR returns Sunday through Tuesday under building
high pressure.
&&
.PBZ WATCHES/WARNINGS/ADVISORIES...
PA...None.
OH...None.
WV...None.
&&
$$
SYNOPSIS...Frazier
NEAR TERM...Frazier
SHORT TERM...Frazier
LONG TERM...Frazier
AVIATION...Kramar
Source:
PBZ issues Area Forecast Discussion (AFD) at Aug 29, 6:59 PM EDT---------------
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