217
FXUS61 KPBZ 251823
AFDPBZ

Area Forecast Discussion
National Weather Service Pittsburgh PA
223 PM EDT Wed Sep 25 2024

.SYNOPSIS...
Gradual lowering of precipitation chances is expected through
Thursday before a potentially unsettled pattern develops Friday
into early next week.

&&

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

- Scattered showers and thunderstorms continue today.

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Broad ascent with weak embedded vortices will promote scattered
showers and low probability thunderstorms through tonight ahead
of a stalled closed low sitting over the lower Ohio River
Valley. A lull between waves (with brief subsidence) is
occurring as of 2pm, with an uptick in activity likely between
4pm-10pm as the next shortwave crosses and the weak surface
front approaches from the west. Despite 30-40kts effective
shear, excessive cloud cover will minimize sfc heating and keep
area instability generally below 1000 J/kg and keep lightning
(let alone severe) risks low. Dry antecedent conditions and
weak convergence also should limit any flooding concerns.

Overnight, the closed Ohio Valley low will begin sagging SW
toward the western TN while a northern trough shifts toward New
England. This will lend to a downward trend in convective
activity given than ideal position relative to various waves.
Little air mass change and excessive cloud cover will maintain
above average temperature.

&&

.SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/...
KEY MESSAGES:

- Mostly dry with seasonable temperature Thursday
- Potential for increasing influence from Hurricane Helene

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Confidence is high in drier weather developing Thursday as the
closed low and remnants of Hurricane Helene remaining well to
the south and Nova Scotia troughing displaced northeast. The
moist airmass will be relatively unchanged, lending to mostly
cloudy skies and lower diurnal fluctuations.

Variation in outcomes increase starting Friday and are largely
defined by the positioning/movement of Hurricane Helene remnants
in conjunction with the west TN closed 500mb flow. Ensemble
means suggest rain chances starting Friday morning south of
Pittsburgh with the initial outer bands of the large area of
low pressure. This assumes the surface low reaching the western
NC/SC border Friday morning and lifting towards eastern KY by
mid-day. Other higher-resolution model forecasts are slower and
farther west with the low track, which favor the outer bands
staying south of the region. Current forecast represents a blend
of the two with higher/lower PoPs south of Pittsburgh possible
in scenario 1/2, respectively.

Low positioning will also influence surface gradient and the
onset of SE wind increases (remaining well below advisory
criteria). Confidence is high for slightly above average
temperature continuing while cloud cover remains plentiful.

&&

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

- Rain chances will continue through the weekend, but no day
  looks like a washout.
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Ensembles are in fairly good agreement in the broad idea of
continued interaction between the TN closed low and Hurricane
Helene remnants Saturday into Monday. The combined low area will
be fairly stationary over the TN River Valley Saturday and
slowly weaken before drifting SE into early next week. Expect
periodic rain chances, abundant cloud cover, and above normal
temperature during this period. Despite the agreement, large
variations exist in the finer scale details of mesoscale
banding, jet placement, and low positioning that will greatly
determine timing/coverage/intensities of rain showers. Though
any given period could see showers, the limitations of
resolution for global models and general pattern recognition
suggest dry conditions are more likely than not with smaller
windows of rain that the forecast lends itself to.

Ensemble means favor a northern stream trough kicking the
sagging low out of the region by mid-week and ushering an
airmass change. That said, scenarios remain on the sagging low
staying farther south while ridging develops near the Great
Lakes; this would foster drier and warmer than forecasted
conditions.

&&

.AVIATION /19Z WEDNESDAY THROUGH MONDAY/...
Scattered showers and thunderstorms will continue through this
evening with the greatest potential for restrictions remaining north
and northwest of PIT. Another large complex of rain can be seen on
recent radar imagery over southern and central West Virginia
gradually moving north towards the local area. This will bring
another round of more widespread shower activity (similar to earlier
this morning) during the late evening and overnight hours.
Restrictions will continue throughout the period at FKL/DUJ, while
other sites that have seen improvement this afternoon will once
again see deteriorating conditions overnight with the onset of the
the next round of rain. Most shower activity should move out of the
area to the east by mid to late morning Thursday, with low cigs
potentially lingering a bit longer before slow improvement occurs
Thursday afternoon.

.Outlook...
Widespread restrictions will linger into Thursday before VFR is
expected to end the week. Periodic rain chances are expected through
the weekend.

&&

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

&&

$$

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