166
FXUS61 KPBZ 160535
AFDPBZ

Area Forecast Discussion
National Weather Service Pittsburgh PA
135 AM EDT Mon Sep 16 2024

.SYNOPSIS...
Dry weather will continue through Monday under high pressure.
Rain chances return Tuesday and continue periodically through
late week with the return of low pressure.

&&

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

- Dry weather continues through tonight under high pressure.
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Update...
Made minor adjustments mainly to the hourly temperatures, based
on the latest surface observations.

Previous discussion...
The slow, northward migration of a coastal low toward the
Carolinas will introduce thicker cirrus for eastern zones and
maintain the surface pressure gradient. The increasing cloud
cover plus enough boundary layer mixing should keep area
temperature elevated (notably along the western slopes of the
Laurel Highlands), which translates to about 5 degrees above the
daily average.

&&

.SHORT TERM /6 AM THIS MORNING THROUGH 6 PM TUESDAY/...
KEY MESSAGES:

- Dry and warm again Monday.
- Low pressure may bring rain chances to the West Virginia
  ridges late Monday night.
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High pressure will remain centered across the northeastern CONUS
to start off Monday, but gradually begins to weaken and shift
east over the northern Atlantic by Monday night as a low
pressure system approaches the area from the south.

Models have maintained their recent westward trend with the
track of the low, indicating it approaches the Lower Ohio
Valley region by Tuesday. Rain chances could begin to increase
from S-N as early as Monday night as moisture and ascent
increase on the northern periphery of the approaching low.
Maintained chance POPs over the WV ridges after Midnight to
reflect this growing potential. Rain chances will increase
further going into Tuesday; more details on that can be found
in the Long Term section below.

Temperatures will be a bit cooler Monday afternoon due to the
breakdown of high pressure and increasing cloud cover, with
highs topping out in the upper 70s to low 80s. Low temperatures
Monday night actually trend a couple degrees warmer than recent
nights due to the increasing moisture and cloud cover, with
most remaining in the upper 50s.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/...
KEY MESSAGES:

- Rain chances return to the region, peaking Wednesday
- Slightly above average temperature will remain before rising
  farther above normal heading into the following weekend
-------------------------------------------------------------------

Global model ensembles are favoring the trend of the coast low
aiding the development of a weak 500mb low near the Upper Ohio
River Valley Tuesday through Thursday. Return flow around this
upper feature and farther NW movement of the surface low will
aid in higher rain probabilities while excessive cloud cover
limits diurnal heating/cooling. Fine scale features remain
harder to diagnose to pinpoint potential moderate rain bands,
overall thunderstorm threat (left slight chance mention but mean
CAPE values struggle to reach 500 J/kg any afternoon), and
potential influence of the prior dry airmass on limiting
accumulations.

Confidence is fairly high on this upper wave/surface low combo
to slowly drift back toward the east coast starting Thursday.
Subsidence in its wake will cause a west to east gradient of
lower rain chances and thinning cloud cover. Increased
insolation and weak height rises should also foster slight
temperature rises through Friday. Longer range outlooks depend
on whether this wave phases with a stronger Nova Scotia trough
to maintain a positively tilted trough (resulting in slightly
cooler temperature and low probability high terrain rain) or
some sort of Great Lakes ridge building (resulting in dry
weather and above normal temperature).

&&

.AVIATION /06Z MONDAY THROUGH FRIDAY/...
VFR is expected to continue through the period as the area sits
on the western edge of a high pressure ridge. A slightly
elevated pressure gradient will provide another opportunity for
daytime easterly gusts at susceptible ports. There is still a
70% or greater chance of gusts less than 20kts in the
afternoon. Gusts will subside overnight with the loss of mixing.

High clouds are expected to increase through the afternoon from
the east as upper moisture from a tropical disturbance advects
in, but there is high confidence this does not impose any
restrictions for the current TAF period.

.Outlook...
Occasional restrictions and showers are possible Tuesday
through Thursday as low pressure slowly tracks from the Carolina
coast to the Ohio Valley region.

&&

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

&&

$$

SYNOPSIS...Cermak
NEAR TERM...WM/Frazier
SHORT TERM...Cermak
LONG TERM...Frazier
AVIATION...Milcarek