-- Discussion containing changed information from previous version are highlighted. --
451
FXUS61 KPBZ 021635
AFDPBZ

Area Forecast Discussion
National Weather Service Pittsburgh PA
1235 PM EDT Thu May 2 2024

.SYNOPSIS...
Dry and warm weather gives way precipitation chances with a
cool-down Friday night through this weekend. Warm and unsettled
weather continues next week.

&&

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

- Dry with above normal temperatures continuing.

-----------------------------------------------------------------

Little has been changed in the prior update save a slight upward
adjustment in temperatures and downward adjustment in dewpoints
to match morning observations. This is consistent with the NBM
under-mixing bias on clear days.

.. Previous Update ..

Another dry day with above normal temperatures on tap for Thursday.
Upper ridge axis builds with high pressure centered just to the
north. The cold front that pushed through overnight Wednesday night
will stall across the Mason Dixon line before lifting back into the
area as a warm front with low pressure off to our west. The primary
challenge will be how far north it gets, and thus how warm we get,
as the high will likely work to suppress its northward progression.
Latest ensemble guidance hangs it around or just south of Pittsburgh
providing 80+% probability of exceeding 80F and while locations
north of Pittsburgh more likely sit in the upper 70s.

With little cloud cover, plenty of insolation, and mixing up to
~800 mb, have leaned toward the low end of guidance for dews
with the NBM`s bias to undermix clear sky days. Upper level
clouds increase tonight as moisture advects in in southwesterly
flow aloft and lows sit in the upper 50s north of I-80 and low
60s further south. Some low probability showers may try to clip
our eastern Ohio zones after sunset, but dry air should win out.

&&

.SHORT TERM /FRIDAY THROUGH SUNDAY NIGHT/...
KEY MESSAGES:

- Unsettled pattern returns for the weekend with rain chances
  beginning Friday night continuing through Sunday.
- Chance of thunderstorms Friday and Saturday.
- Temperatures drop, but still remain above normal.
-------------------------------------------------------------------

The pattern then becomes more unsettled into the weekend as
ensembles shunt the upper ridge beginning with a leading shortwave
arriving on Friday. With the ridge pushing off to the east, deep
layer southwest flow will increase moisture and showers and
thunderstorms develop Friday afternoon ahead of approaching low
pressure. Hi-res ensemble probability for >500 J/kg of CAPE
increases to 50-60% Friday afternoon, but further destabilization
should be limited given fairly consistent ensemble agreement in a
good amount of cloud coverage around. In addition, weak deep layer
shear (low probabilities for >30 knots) and warm mid-levels
potentially putting a lid on updraft growth will limit concerns for
severe weather. Friday will be the warmest day of the week despite
the increasing cloud cover with widespread mid 80s likely in deep
southwest flow. Highs tapping into the low 90s aren`t out of the
question either with 850 mb temperatures of 16-18C. Latest ensemble
probability is 50-70% for Pittsburgh south and west and some record
highs may be approached (see Climate section).

Rain chances continue through the weekend with several more rounds
of shortwaves accompanying the passing low pressure. With the best
overlap of forcing for ascent on Saturday, it appears that the
daytime hours will likely be the wettest of the weekend. Ensemble
probability for >1" of rain in any 24 hour period remains 30% or
lower, but that said, the combination of a deep saturated profile
characterized by mean precipitable water values between 1.2-1.4"
(nearing the daily climatological max) and modest instability could
result in periods of heavier rain with any convective elements and
thus a localized flood threat especially for urban and low lying
areas on Saturday. Spread in ensemble 24 hour QPF ending Saturday
night depicts this uncertainty with mean values around 0.5-0.75" but
the potential for up to 1.75" exists on the upper end of the
spectrum. The Weather Prediction Center has maintained the Marginal
Risk (1/5) for excessive rainfall on Saturday. Sunday will
feature continuing rain chances, but latest ensemble runs favor
the second half of the weekend to see lower amounts. All told,
ensemble probability for >1" total through Sunday night sits
around 50-60%.

Thick cloud coverage through the weekend will hold temperatures in
check, but still above average, in the 70s.

&&

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

- Rain chances continue into early next week but more uncertainty
  lends lower confidence.
- Temperatures favored to remain above normal.
-------------------------------------------------------------------

A brief lull in the precip is favored late Sunday night into early
Monday morning as upper ridging slides through and surface high
pressure meanders on by. Uncertainty with its strength and timing
due to ensemble differences in a passing upper wave to the north and
another digging shortwave and associated low pressure moving across
the Tennessee Valley lends lower confidence to the start of the next
workweek, but regardless rain chances ramp back up later
Monday. A stronger ridge and thus less rainfall is the most
likely ensemble solution at this time, but a quicker breakdown
of it could give us another decent shot of rain through Tuesday.
The amplified pattern continues into mid-week with unsettled
weather in store.

&&

.AVIATION /18Z THURSDAY THROUGH TUESDAY/...
-- Changed Discussion --
VFR conditions and light winds will continue through the TAF
period. As upper ridging shifts east, shower and thunderstorm
chances increase later Friday afternoon and into the evening as
a warm front lifts north across the region.

.Outlook...
Restriction potential will continue through Saturday and again
early next week as multiple disturbances cross the region.
-- End Changed Discussion --

&&

.CLIMATE...
Some record high temperatures may be approached on Friday.
(* denotes current forecast temperature exceeds value)

               Record High   Year
Pittsburgh          95       1887
Wheeling            90       1942
Morgantown          88*      1965, 2012
New Philadelphia    89       2012
Zanesville          91       1938
Dubois              84       2012

&&

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

&&

$$

SYNOPSIS...Milcarek
NEAR TERM...MLB/Milcarek
SHORT TERM...MLB
LONG TERM...MLB
AVIATION...22/88
CLIMATE...