350
FXUS61 KPBZ 180510
AFDPBZ

Area Forecast Discussion
National Weather Service Pittsburgh PA
110 AM EDT Wed Sep 18 2024

.SYNOPSIS...
Some limited rain chances, best in the ridges southeast of
Pittsburgh, will be present into Wednesday night thanks to
slow-moving low pressure. Rainfall should be light in most
cases. Dry weather returns for Thursday and through the
weekend.

&&

.NEAR TERM /UNTIL 6 AM THIS MORNING/...
KEY MESSAGES:

- Best rain chances along east-facing slopes tonight; more
  limited towards Pittsburgh
- Above-normal overnight lows are forecast
-------------------------------------------------------------------

Evening update...biggest question is how far east any overnight
showers will be able to reach. Much of the latest model data is
keeping the best chance for rain over the ridges and low lands
on the western edges. Additionally, the eastward movement of
the showers have slowed from previous runs. Tried not to stray
too far from the previous forecast, but have slowed the westward
progression of the PoPs. Rest of the forecast is in good shape.


Previous discussion...

Vertically-stacked low pressure continues to rotate in the
vicinity of the Carolinas, and will continue to do so through
tonight. As moisture and vorticity lobes continue to lift
northward with time, some modest rain chances will eventually
reach to a Zanesville/Pittsburgh/Indiana PA line tonight.
However, the previously mentioned challenges of dry air and
downslope flow, plus little northward progress of the surface
system, will tend to keep rainfall spotty and light for the most
part. Upslope- prone areas, particularly eastern Tucker County,
have the best chance of getting meaningful rain. The cloud
increase will keep temperatures 5 to 10 degrees above
climatology tonight.

&&

.SHORT TERM /6 AM THIS MORNING THROUGH THURSDAY NIGHT/...
KEY MESSAGES:

- Low rain chances expand across area Wednesday, still highest
  in the ridges
- Dry weather returns by Thursday
- Seasonable temperatures Wednesday, returning to above average
  readings by Thursday
-------------------------------------------------------------------

The slow-moving, stacked low pressure system will continue to rotate
in the general vicinity of the Carolinas through Wednesday,
before opening up into a broader trough that will position
itself over the Mid-Atlantic and New England areas by Thursday.
Moisture/vorticity lobes will continue to rotate around the low,
reaching further north into our region by Wednesday, such that
most of the CWA has at least a mentionable chance of measurable
rain. By Wednesday night, as the eastward transition of the
system takes place, rain chances drop off in coverage, largely
limited to the ridges, before ending on Thursday as a developing
ridge starts to push up the Ohio Valley.

The models continue the overall bleak outlook for wetting rain for
many locations. When looking at the potential for 0.10" or more of
rain over the entire event, the 13Z NBM keeps 50 percent or greater
probabilities near and to the south of I-70, with eastern Tucker
County still seeing the best chances (here, there is a 50/50 shot of
a half-inch). Locations north of I-80 have a slightly higher than
even chance of seeing no measurable rain whatsoever.

The expected cloud cover and potential light rain will limit the
diurnal temperature range Wednesday/Wednesday night, with highs near
climatology and lows a touch above normal.  Decreasing clouds on
Thursday will lead to a warmer day, with values going above normal
once again.

&&

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

- Dry weather through the weekend, very low rain chances early
  next week
- Above average temperatures through early next week
-------------------------------------------------------------------

Model ensembles are in good agreement that the developing ridge to
our west will slowly build eastward, extending from the Texas Gulf
coast into eastern Canada by Saturday. This will also push the East
Coast trough further offshore with time. As a result, dry weather
and above-normal temperatures are forecast for Friday through Sunday
with high confidence.

Uncertainty ticks up a bit with the new work week.  A new trough
approaching from the Northern Plains/Upper Midwest has at least some
potential to weaken the ridge during the Monday/Tuesday period,
which would lead to cooler temperatures and an uptick in rain
chances.  However, cluster analysis shows that the majority of
ensemble members largely maintain the ridge over our region, which
would tend to keep the dry and warmer-than-normal pattern going. For
now, the forecast for early next week will lean towards this latter
scenario, pending future model runs.

&&

.AVIATION /06Z WEDNESDAY THROUGH SUNDAY/...
VFR is expected overnight with mid and high cloud cigs on the
northern side of a low pressure system, which was centered
across the western Carolinas. The low will drift toward the Mid
Atlantic region today, as moisture and ascent/vorticity
advection rotate around it. Expect a lowering cig, as moisture
increases in the lower and mid levels. Most airports will see a
cig at or below 5kft east of a BVI-HLG line. LBE and MGW should
see MVFR cigs developing by mid morning, with better low level
moisture and limited rain chances.

Any MVFR should return to VFR by late afternoon/early evening,
as lower level moisture begins to decrease. A persistent east
wind is expected at around 5 kt.

.Outlook...
Occasional restrictions and showers are possible, especially
near MGW/LBE, through early Thursday, as the low slowly tracks
across the Lower Ohio Valley and Appalachians region. VFR is
then expected through Sunday as high pressure builds in.

&&

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

&&

$$

SYNOPSIS...CL
NEAR TERM...22/CL
SHORT TERM...CL
LONG TERM...CL
AVIATION...WM