923
FXUS61 KPBZ 191721
AFDPBZ

Area Forecast Discussion
National Weather Service Pittsburgh PA
121 PM EDT Thu Sep 19 2024

.SYNOPSIS...
Save shower and storm chances in the West Virginia high terrain
today, dry weather and above average temperatures will prevail
through late week. Chances of showers and storms return
Saturday, followed by higher chances early next week.

&&

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

- Drier and warmer for most today.
- Shower and storm chances for the West Virginia high terrain.
-------------------------------------------------------------------

Made some relatively minor adjustments to PoPs and sky cover to
account for recent trends, but the overall forecast remains on
track.

Previous discussion...

The advertised coastal low is expected to meander to the east
throughout the day today, bringing mostly clear skies. Highs
will top out above normal. Mid- level flow will modulate
northerly with low- level flow orienting more northeasterly for
the day Thursday. Flow and subsidence is forecast to dry out
and stabilize areas north of I-70. Elsewhere, moisture may be a
bit slower to clear. When combined with heating and 100-300
J/kg MLCAPE, a few showers and storms may be possible today
south of I-70, most likely in the higher terrain of West
Virginia with orographic forcing. There is a >50% chance all
additional totals are less than 0.25" in eastern Tucker, >20%
elsewhere.

Clear skies, calm winds, and elevated surface moisture
(particularly in areas where it rained today), will prime the
area for patchy radiative fog formation into the morning hours
Friday. Coverage will be more likely in insulated valleys and
river valleys, and clear after daybreak. Friday will maintain
the mostly clear skies under high pressure with temperatures
around 10 degrees above average.

&&

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

- Chances of showers and storms Saturday afternoon.
---------------------------------------------------------------------

Ensembles have come into a bit more agreement on a shortwave
passage during the day on Saturday that will act to flatten the
main ridge axis and cool upper levels. This may allow for a bit
of instability generation. Roughly 500 to 1000 J/kg SBCAPE are
possible should conditions trend toward the 50th to 90th
percentile. While flow is quite weak in the low levels, it
accelerates aloft to around 30 to 40kts at 6km. Positioning in
the left exit region of the jet will further encourage ascent.
Ensemble mean DCAPE is around 800 J/kg. All clustered ensemble
scenarios show at least a 50% chance of precipitation somewhere
in the forecast area, with a 30% probability of thunder. All
things considered, if the environment is toward the higher end
of the instability distribution, low- end severe potential
remains Saturday afternoon and evening coincident with the best
forcing and time of day as the shortwave passes through. Given
modeled profiles, wind and hail would be the primary threats.
If instability is towards the lower end of the distribution,
severe threats will be low to none. Because of storm motion of
20 to 30 kts perpendicular to the forcing axis, flooding
threats (and notable rain mentions), remain limited.

Rain chances decrease overnight as the wave passes to the east
and localized decent sets in. Patchy fog will remain possible
yet again, particularly if rain does occur.

&&

.LONG TERM /SUNDAY THROUGH WEDNESDAY/...
KEY MESSAGES:

- Ridging and warm temperatures to start the week will likely
  give way to seasonable temperatures with precipitation chances
  as the week progresses.
-------------------------------------------------------------------

After the shortwave passage, brief ridging is expected to set
in again with high confidence. Ensemble clusters are beginning
to indicate that the Sunday will be the warmest day of the
period. By Monday, clusters attempt to shunt the ridge axis
east, with some keeping it around until Tuesday. This will
govern when precipitation chances begin.

For Tuesday and beyond, however, there is medium to high
confidence a digging midwest trough will leave our area
synoptically favored for cyclogenesis and storm tracks, more-so
than we have seen this month. This will supply daily rain
chances, and perhaps some relief to drought. Given this is still
roughly 4 to 5 days out, a lot of the particulars about
rainfall will be ironed out once confidence increases in low
track(s).

&&

.AVIATION /17Z THURSDAY THROUGH MONDAY/...

Lingering CU is expected to dissipate from north to south
through the late evening with increase mid-level subsidence.
Winds will continue to remain light to variable from the
north/northeast.

Patchy early morning fog is possible Friday, especially for
FKL/DUJ, with radiational cooling and light wind. Otherwise,
VFR is expected Friday under high pressure.

.Outlook...

Low chances for restrictions in thunderstorms are possible
Saturday with a crossing shortwave trough.

VFR returns Sunday under high pressure before restriction
potential returns Monday with an approaching warm front.

&&

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

&&

$$

SYNOPSIS...Milcarek
NEAR TERM...CL
SHORT TERM...Milcarek
LONG TERM...Milcarek
AVIATION...Hefferan