766
FXUS61 KPBZ 200945
AFDPBZ

Area Forecast Discussion
National Weather Service Pittsburgh PA
545 AM EDT Fri Sep 20 2024

.SYNOPSIS...
Seasonably hot weather is expected through the weekend with a
marginal chance of severe storms Saturday, mainly east of I-79.
A wetter pattern is becoming increasingly likely next week.

&&

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

- Seasonably hot weather; record breaking heat potential for New
  Philadelphia and DuBois.
-------------------------------------------------------------------

Any lingering fog is expected to clear rapidly beyond sunrise
with mixing. Temperatures are expected to climb rapidly into the
day today with upper ridging and surface southerly flow under
high pressure. With how warm conditions have been, it is
difficult to believe the average high for Pittsburgh this time
of year is 74. With temperatures forecast to climb into the 80s
(and even 90s for eastern Ohio), highs will be around 10 to 15
degrees above average. New Philadelphia has a shot at beating
their record high of 89F (2002), and DuBois may approach their
record high of 84F (1965).

Temperatures will cool under clear skies tomorrow night, but
should be limited by dew points and light winds. This will keep
lows slightly above average. Fog appears less likely overnight
save insulated valleys with larger dew point depressions and
some winds.

&&

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

- Marginal severe storm potential, mainly east of I-79 with the
  primary threat being damaging winds.
---------------------------------------------------------------------

Guidance still remains optimistic on precipitation chances
Saturday for western Pennsylvania and eastern Ohio as a
shortwave overtops and flattens an eastern ridge. This will act
to cool upper levels and keep daytime highs slightly cooler
than the day prior, but the main question remains severe
potential.

First, the environment looks favorable for low-end severe
threats. Probabilities of at least 1000 J/kg of SBCAPE are up to
50% to 75%, while chances of 30kts to 40kts of shear in the
0-6km layer remain elevated, though most of the shear is
confined to the mid-levels. Mid-level dry air in shortwave
induced subsidence is also likely to supply as much as 800-1000
J/kg DCAPE. This suggests winds remain the primary threat. So
the main question for development is not the environment, but
rather the forcing.

There is still spread in the intensity and timing of the mid-
level vort max. Passage could be as reasonable early as 14Z and
as late as 22Z. The later the passage time, the more the wave
will be able to utilize instability, and thus, the higher chance
of severe weather. The second uncertainty is intensity. The
forcing will need to be strong enough to overcome mid-level dry
air. A number of CAMs suggest this, but roughly an equal number
rely on orographic help, leaving the primary threat east of the
forecast area. These uncertainties have justified the
maintenance of a marginal risk for severe weather.

Chances of any rain with this wave range from 50% in eastern
Ohio to 90% east of Pittsburgh. Despite this, chances of 0.25"
of rain only maximize at 50% to 60% in western Pennsylvania.
This will do little in the ways of drought relief.

Rain chances taper overnight as the wave passes to the east and
subsidence fills in behind. Fog is possible Saturday night and
Sunday morning given calm, clear conditions and recent rainfall.

&&

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

- Hot and dry Sunday.
- Precipitation chances encroaching for the rest of the week
  with moderating temperatures.
-------------------------------------------------------------------

There remains high confidence in brief ridging Sunday which
will allow high temperatures to remain well above average.
Chances of topping 90F are 20% to 40% in eastern Ohio, with 80s
forecast elsewhere.

By Monday, there is more agreement that the ridge axis flattens
to quasi-zonal flow, but uncertainties in the 500mb flow
snowball by mid-week. All clustered guidance indicates some
troughing, however, roughly 40% of global ensemble membership
has a positively tilted Midwest trough, while 60% has a neutral
eastern trough by the middle of next week. A Midwest trough
would be more conducive to low tracks over our area and more
precipitation, while a eastern trough still allows precipitation
chances, but the main QPF axis would be toward the eastern
seaboard.

However you cut the cards, this is the best shot of notable
rain this month, with chances of greater than an inch of QPF 50%
for eastern Ohio and northern West Virginia and 60% to 70% in
western Pennsylvania.

&&

.AVIATION /10Z FRIDAY THROUGH TUESDAY/...
Patchy early morning fog is possible with efficient radiational
cooling and light winds, primarily for FKL/DUJ but also
possibly around MGW/LBE (though generally shorter duration and
less dense at the latter terminals).

Otherwise, VFR and light winds are expected throughout the TAF
period. Scattered diurnal CU should develop during late morning
and afternoon with bases starting in the 3-5kft range, gradually
lifting to 6-8kft before dissipating around sunset.

.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 early
next week with an approaching warm front.

&&

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

&&

$$

SYNOPSIS...Milcarek
NEAR TERM...Milcarek
SHORT TERM...Milcarek
LONG TERM...Milcarek
AVIATION...Cermak/Hefferan/22