333
FXUS61 KPBZ 101833
AFDPBZ

Area Forecast Discussion
National Weather Service Pittsburgh PA
233 PM EDT Fri May 10 2024

.SYNOPSIS...
Scattered showers give way to dry conditions 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 TONIGHT/...
KEY MESSAGES:

- Scattered showers tapering off this evening with areas of fog
  possible by sunrise.
- Lows tonight 5-7 degrees below average.
-------------------------------------------------------------------

Scattered showers continue this afternoon aided by an inverted
surface trough extending out from low pressure across Delmarva and
weak shortwave energy traversing an upper trough across the
Northeast. Coverage has transitioned to more of a convective look as
low and mid level drier air noted on water vapor satellite continues
to advect with mid level flow backing more west of north through the
afternoon. As the surface low pushes offshore, one last upper wave
will dive through late this afternoon and help maintain the
scattered showers owing to some shallow instability up to 200-
300 J/kg. No severe weather or flooding concerns are expected.

Once forcing is 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 areawide which is a good 5 to 7 degrees below normal. With
lingering low level moisture and light wind overnight, fog may form
toward sunrise with hi res ensemble probabilities for < 1 mile up to
50-60% further south and east of Pittsburgh.

&&

.SHORT TERM /SATURDAY 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 /19Z FRIDAY THROUGH WEDNESDAY/...
Light rain showers, increasing in coverage between 18z-22z,
rising cig heights are expected through this evening. Intrusion
of drier air as low pressure exits east will erode showers and
cigs during the early evening hours, resulting in areawide VFR
conditions.

The combination of residual boundary layer moisture, some cig
deck clearing, and light wind may promote fog formation during
the pre-dawn hours Saturday morning. Highest probabilities are
along the higher terrain east/southeast of KPIT where daytime
showers will linger longest and drier air will be late on
arrival (KMGW/KLBE/KDUJ).

A cold front will approach from the NW at the end of the TAF
period, producing a swath of light rain showers with low
probability for thunder.

.Outlook...
Additional restrictions are likely in conjunction with the
mentioned showers and low probability thunderstorms above.
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.

&&

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

&&

$$

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