-- Discussion containing changed information from previous version are highlighted. --
554
FXUS61 KPBZ 232243
AFDPBZ

Area Forecast Discussion
National Weather Service Pittsburgh PA
643 PM EDT Thu May 23 2024

.SYNOPSIS...
Showers and storms are likely to develop south of Pittsburgh
after 5pm today with a new disturbance. Foggy conditions are
expected overnight into early Friday south of Pittsburgh, PA.
Periodic thunderstorm chances are expected through the holiday
weekend as a series of upper level disturbances cross the
region.

&&

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

-Ridging over the region will keep the area mostly dry through
 through 6pm.
-A disturbance to our south will advance late this afternoon and
 stir up showers and storms late this evening into the overnight
 hours; probabilities are high south of I-70 for convection
 redevelopment.
-Fog is expected to develop south of Pittsburgh during the
 overnight hours under warm, moist airmass.

_____________________________________________________________

A stationary boundary is currently situated between
Morgantown,WV and Pittsburgh,PA early this morning. A few
showers are stirring in northern West Virginia within a warm,
moist airmass (dew points south of I-70 are still in the
mid-60s). Lightning probabilities are low given convection is
below the freezing level (10kft).

Elsewhere, drier air from the north has advanced in the wake of
the late night passing front and cloud coverage has decreased.
Warm, dry conditions are likely to last for a large portion of
the region under ridging. However, Hi-Res models have been
consistent that a shortwave late this evening from the south
will cause redevelopment of showers and storms after 6pm.
Instability will be plentiful (1000J/kg to 1500J/kg) during the
passing of the shortwave. However, shear will be mostly weak
(effective shear less than 30kts). A few storms may be
considered strong south of I-70 with DCAPE values ranging
between 500J/kg to 700J/kg for a brief time period.

The probability of strong storms will likely decrease as we
approach midnight as outflow from lingering convection decreases
the potential of dry, cool cores surging to the surface. The
threat will likely evolve to heavy rain due to slow moving
storms.

The potential for fog late tonight increases in the vicinity of
the stalled boundary and where showers and storms were
considered robust and/or long lasting.

&&

.SHORT TERM /6 AM FRIDAY MORNING THROUGH SATURDAY/...
KEY MESSAGES:


-Lingering showers from a passing shortwave may last through
 late morning Friday south of Pittsburgh, PA.
-Probability of showers and storms decrease Friday afternoon.
-A crossing shortwave will return the risk for showers and
 storms early Saturday
 _____________________________________________________________

Remnant moisture south of Pittsburgh,PA may keep convection
ongoing south of I-70 into the late morning hours of Friday with
an exiting shortwave. Elsewhere, high pressure will likely keep
quiet, dry weather is expected. Afternoon high temperatures for
Friday and overnight lows early Saturday will range 5 to 10
degrees above average.

Ridging will break down across the Ohio River Valley early
Saturday morning as an ejecting low out of the northern Dakota
tracks into the Great Lakes. With a flux of low-lvl moisture
early Saturday morning, our environment has the potential for
strong to severe storms and excessive rainfall late Saturday
afternoon/evening. MUCAPE ranges between 1500J/kg to 3000J/kg
over western PA/eastern OH. Given a storm with a nice updraft,
hail and downbursts may be a threat. However, some models
suggest very little triggering for lift despite a decent
environment. So confidence is still somewhat low on this
scenario.

&&

.LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/...
KEY MESSAGES:

- Variability remains high on long term forecast and may be
  predicated on prior day`s convective outcomes.
- Overall, periodic showers and thunderstorms with slightly
  above normal temperature is favored through the holiday
  weekend and into next week.
  ____________________________________________________________

A strong, well-organized low pressure system is becoming the
favored pattern towards the end of holiday weekend in the Ohio
River Valley. Timing and the position of the center of the low,
along with environmental moisture profiles, are currently not
in phase between the long range models and some of the newer
runs of the CAMs. There is a very large difference between
800J/kg (GFS) to 3000J/kg (NAM). At the moment, the Storm
Prediction Center (SPC) has focused the convection outlook
southwest of our county warning area (CWA). However,
probabilities of organized convection (a combination of shear
and instability) may shift northeast if model runs come to an
agreement in the next 24 to 36 hours.

Long range suggests a shift to a cooler, dry pattern by the
middle of next week as upper troughing develops over the Great
Lakes. Expect temperature to fall below the seasonal average,
with Tuesday potentially being the transition day from shower
activity to dry weather.

&&

.AVIATION /00Z FRIDAY THROUGH TUESDAY/...
-- Changed Discussion --
VFR and light wind are favored through the TAF period under the
influence of high pressure to the north.

A weak boundary sitting near the I-70 corridor plus weak
shortwave movement may foster isolated southeast-moving
convection between 02z-08z. Lightning is possible, but terminal
impact remains low with hi-res model trends bearish on storm
intensity. If heavy rains develops, pockets of fog may form as
the near-surface layer moistens. The overall threat for fog is
lowering from prior outputs due to likely cirrus coverage
limiting radiational cooling overnight as convection continues
well south of the region.

.Outlook...
Shower and thunderstorm chances return Saturday afternoon and
evening, but may be dependent on evolution of storms that occur
across the western Great Lakes. Any thunderstorms poses a risk
for gusty, erratic winds and lowered visibilities.

Thunderstorm probabilities are highest late Sunday into Monday
as a more robust low pressure system moves through the Great
Lake region. A pattern shift thereafter will introduce periodic
precipitation chances and potential for more prolonged cig
restrictions.
-- End Changed Discussion --

&&

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

&&

$$

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