-- Discussion containing changed information from previous version are highlighted. --
244
FXUS61 KPBZ 102352
AFDPBZ

Area Forecast Discussion
National Weather Service Pittsburgh PA
752 PM EDT Fri May 10 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 /THROUGH SATURDAY/...
KEY MESSAGES:

- Showers tapering off this evening with areas of fog possible
  by sunrise.
- Lows tonight 5-10 degrees below average.
-------------------------------------------------------------------

Forcing and daytime instability 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 /SATURDAY NIGHT 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.
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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.
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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 /00Z SATURDAY THROUGH WEDNESDAY/...
-- Changed Discussion --
The remaining isolated rain showers will continue to dissipate
through 02Z as daytime heating is lost and as a shortwave trough
exits to the east. Areawide VFR conditions will remain in
control through midnight or so. Scattered clouds are more likely
to linger east of PIT than to the west.

Lingering low-level moisture, decoupling wind, and scattered
clouds will likely result in some fog formation overnight.
NBM/HREF probabilities continue to favor locations east of PIT,
and have hit the fog hardest at DUJ/LBE/MGW. To the west, lower
probabilities are indicated as drier air will be building in
late. Fog is expected to break up in the 12Z/13Z period.

A cold front will approach from the NW at the end of the TAF
period, producing another round of rain showers, with possible
thunderstorms in marginal instability. Expecting MVFR
restrictions with these showers. Have tried to time period of
greatest thunder chances with 3-4 hour VCTS periods in the TAFs.

.Outlook...
Scattered light rain showers will linger into Saturday night as
the upper trough axis crosses. VFR returns Sunday and Monday
under high pressure, before low pressure returns restriction and
precipitation potential on Tuesday.
-- End Changed Discussion --

&&

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

&&

$$

SYNOPSIS...MLB/Milcarek
NEAR TERM...MLB/Milcarek
SHORT TERM...MLB
LONG TERM...MLB
AVIATION...CL/Frazier