-- Discussion containing changed information from previous version are highlighted. --
968
FXUS61 KPBZ 110527
AFDPBZ

Area Forecast Discussion
National Weather Service Pittsburgh PA
127 AM EDT Sat May 11 2024

.SYNOPSIS...
Dry conditions and mostly clear skies are expected overnight
ahead of approaching low pressure that will return showers and
thunderstorms for Saturday and lingering into Sunday.
Temperatures will be below average this weekend. Warmer pattern
returns next week with rain chances increasing again for Tuesday
and Wednesday.

&&

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

- Areas of fog overnight
- Lows tonight 5-10 degrees below average.
-------------------------------------------------------------------

Update...
Made some minor adjustments to the overnight forecast based on
the latest observations and near term model data. Otherwise the
forecast remains on track.

Previous discussion...
Forcing will be lost tonight as dry air wins out and brief
shortwave ridging builds, dry conditions will ensue. Light wind
will flip southerly overnight as a southwesterly gradient
establishes ahead of approaching low pressure. Low temperatures
tonight will dip into the low 40s and perhaps even upper 30s
areawide which is a good 5 to 10 degrees below normal. With
lingering low level moisture and light wind overnight, fog may
form toward sunrise east of I-79. Some dense fog may be possible
for areas that clear out and in river valleys through PA and
WV.

The current aurora forecast favors mostly clear skies overnight
west of and including the Pittsburgh metro. With fog mentions
more limited the farther west you go, viewing conditions should
remain favorable should the auroras materialize in eastern
Ohio. Viewing conditions will deteriorate the farther east you
travel into PA and WV with fog and low stratus.

&&

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

- Warm front followed quickly by a cold front brings another shot of
  showers and thunderstorms.
- Highs nearly 10 degrees below average.
-------------------------------------------------------------------

Another upper wave dives southeast out of the Great Lakes Saturday
as aforementioned low pressure tracks by to our north and its warm
front reintroduces rain showers. Hi res ensemble timing is in good
agreement on arrival of precipitation into eastern OH after 11am,
PIT 2pm, and the ridges 3pm with even the earliest and latest timing
only an hour to two on either side of the most likely. Overall
totals with the warm advection driven precip should be light between
0.2-0.3".

The cold front then arrives quickly after leaving us little time in
the open warm sector. Southerly gradient flow will try to pull in
warmer and more moist air but only have a short window to do so.
Scattering of the cloud deck appears low probability, so this should
help to keep instability in check ahead of the cold front. That
said, hi res ensemble mean CAPE values range from 400-600 J/kg
across the area with the 90th percentile closer to 900 J/kg
(contingent on low probability clearing). Effective shear values
should reach 20-25 knots and mostly southeasterly unidirectional.
Combined with decent low and mid level lapse rates of 7-8 C/km, the
environment may be able to support some gusty wind and small hail
from the taller cores that manage to develop. Probability of
exceeding 0.5"/hour rainfall rates are sub 30%.

With clouds being dominant for most of the day and rain arriving by
late morning, erred slightly below NBM for highs which should be
just around either side of the 60 degree mark.

Scattered showers may linger into the day on Sunday as the core of
the 500 mb low gets closer overhead and the occluding surface low
throws a weak trough across the area with lingering low level
moisture. Additional rainfall totals look minimal and highest totals
will be along the ridges with upslope enhancement. High pressure
wins out by late afternoon with dry weather returning.

&&

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

- Temperatures rebound into next week.
- Showers and thunderstorms return Tuesday/Wednesday.
-------------------------------------------------------------------

Upper ridging takes hold come Monday with surface high pressure
establishing to our southeast. Uncertainty with the depth of an
upper low well off to our north in Canada lends low confidence
precipitation chances north of I-80. The most likely ensemble
solution brings light rain there for the first half of the day,
though a less likely solution with a weaker low would keep the rain
further north. Pittsburgh and south should stay dry regardless.

More widespread rain chances then arrive for Tuesday and Wednesday
as low pressure ejects out of the Plains and high pressure breaks
down. At this point, machine learning doesn`t indicate any potential
for severe weather. Ensemble total precipitation sits around a
30-60% chance of >0.5" by Wednesday night. Tuesday will be the
coolest day of the week owing to plentiful cloud cover and
precipitation. Much more ensemble spread is exhibited by the
latter half of the week with a developing trough to our west,
but a dry period to close out the week with rain returning for
the weekend looks more likely than not.

&&

.AVIATION /05Z SATURDAY THROUGH WEDNESDAY/...
-- Changed Discussion --
Most airports east of the OH/PA border will see at least patchy
MVFR fog through early Saturday morning. Areas that cleared
late, such as FKL, DUJ, LBE and MGW, have a better potential at
IFR/LIFR fog. This fog should dissipate by 13Z as surface winds
and mixing increase.

A band of showers is expected to cross the region later this
morning into the afternoon under warm advection ahead of an
approaching cold front. MVFR visibilities are expected with
these showers.

The band of showers should exit the region by late afternoon.
Numerous showers and scattered thunderstorms are then expected
to develop along the cold front. Sufficient wind flow aloft, and
a low freezing level, should result in gusty wind and small
hail in some of the storms.

The cold front will exit the region this evening, with most
sites returning to VFR. A crossing upper trough will maintain
showers across FKL and DUJ, where MVFR is expected to continue.

.Outlook...
Restrictions are possible Saturday night and early Sunday under
a trough of low pressure. VFR returns Sunday afternoon through
Monday under high pressure. Restriction potential returns Monday
night through Wednesday under crossing low pressure.
-- End Changed Discussion --

&&

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

&&

$$

SYNOPSIS...MLB/Milcarek
NEAR TERM...WM/MLB/Milcarek
SHORT TERM...MLB
LONG TERM...MLB
AVIATION...WM