786
FXUS61 KPBZ 031345
AFDPBZ

Area Forecast Discussion
National Weather Service Pittsburgh PA
945 AM EDT Fri May 3 2024

.SYNOPSIS...
Dry and unseasonably warm weather precedes increasing
precipitation chances Friday afternoon and continuing through
the weekend. Cooler, but still above average, temperatures
prevail Saturday and Sunday with warm and unsettled weather
continuing into next week.

&&

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

- Showers and thunderstorms Friday afternoon and evening.
- Temperatures well above average approaching a few records.
-------------------------------------------------------------------

Did another minor refresh to the grids for today. Do think that
the thickening cirrus will mute the temperature rise slightly today,
and have 84-87 degrees as a top-end range for much of the area.
Although a shower or two may creep into the ZZV area this
morning, the bulk of the shower/thunderstorm activity is still
projected to kick off during the mid to late afternoon hours.

.. Previous Update ..

High pressure will retreat off to the east as a disturbance
approaches from the west. Cirrus coverage will thicken and lower
through the morning with increasing upper level moisture. Forecast
soundings suggest another day similar to Thursday with a
quickly breaking nocturnal inversion and a dry boundary layer
allowing for mixing up to nearly 700 mb. The 850 mb ridge will
gradually shift to the east and allow for warm advection in
southwesterly flow to bring layer temperatures up to 15-16C
across the area by afternoon, suggesting that high temperature
will achieve the mid to upper 80s despite the cirrus. A couple
sites have the potential to approach record highs (see climate
section). Some lingering uncertainty in ensemble cloud coverage
with suggestions for periods of scattering as cirrus push to the
east lends potential for additional insolation to push
temperatures up even a degree or two higher than currently
forecast. This also could aid in a bit more destabilization
ahead of showers and thunderstorms expected to develop by
afternoon.

Indications are that showers and storms pop after 17z despite
copious low level dry air (LCLs 6-8kft) as convective temperatures
are met and a shortwave moves through, though weak net height rises
through the day are expected. Mean hi res ensemble CAPE has
increased in the latest run with 600-900 J/kg; conditional on
potential scattering of clouds, the 75th percentile is up to 1400
J/kg. Most guidance suggests that warm mid-levels will suppress
updrafts with an equilibrium level below about 500mb. Latest
CAMs suggest that the best shot for deeper convection may be
across eastern Ohio where slightly less warmth and moisture in
the mid-levels may allow for greater vertical growth. Even if
the higher end of the instability spectrum is achieved, weak
cloud bearing layer flow will present a moderate CAPE/low shear
environment likely more favorable of gusty wind with brief heavy
downpours. PWATs will be pushing 1.5" and upwind propagation
vectors around 10 knots despite practically no low level jet
suggest this potential. HREF probs for >0.5"/hr rates reach up
to around 60% by evening. As a result, the Weather Prediction
Center has our area in a Marginal Risk (1/5) for excessive
rainfall on Friday.

Record low max temperatures may be broken Friday night with
persistent cloud cover not allowing for radiative cooling.
Convection is favored to wane as instability is lost and the upper
wave departs. Nonetheless, scattered showers will continue overnight.

&&

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

- Unsettled pattern remains with rain chances continuing
  through Sunday. Thunder possible on Sunday.
- Temperatures drop, but still remain above normal.
-------------------------------------------------------------------

Come Saturday, there is some suggestion the trough progression will
come to a halt and allow rain to persist ahead of it being
reinforced by approaching low pressure and additional shortwave
support arriving from the south. The positioning of the trough will
have a great influence on the weekend weather. No significant
changes to the forecast for Saturday as instability looks limited to
the western side of the stalled boundary/trough with a 50-60% of
>500 J/kg while elsewhere plenty of low to mid level warm air
will cap the environment. Total rainfall Saturday is favored in
the half to three quarters of an inch range.

There is good agreement the trough finally pulls through by
Sunday. An area of maximized precipitation ahead of or just
along the trough axis is favored, as is a greater chance for
more instability to work with. Ensemble probability for CAPE
>500 J/kg reaches 70-80% Sunday, but with a good amount of
clouds around and a low probability of any scattering. Still,
with a bit better dynamics in play and marginal instability, a
few thunderstorms accompanying the trough appear possible. Most
likely total precipitation amounts Friday night - Sunday night
sit around 1.0-1.3", but the 90th percentile exceeds 2"
primarily across the WV panhandle and western PA resultant of
some convective enhancement along the aforementioned trough.
This does not raise any flooding concerns for now, but may
warrant watching if the higher end becomes more likely.

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

&&

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

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

After a brief lull in the precip late Sunday night into early Monday
morning as flat upper ridging slides through and surface high
pressure meanders on by, rain chances again increase. Seeing some
better ensemble agreement for Monday with shortwave low pressure
approaching from the southwest but weakening as the responsible
upper wave flattens out. High pressure to the north should keep the
highest precipitation chances south of I-70. Much more ensemble
spread comes into play after Monday primarily with the progression
of the upper pattern as ridging tries to develop but a deep upper
low across the Dakotas throws shortwave energy to the east and tries
to break the ridge down. A warm front likely lifts through sometime
Tuesday into Wednesday increasing rain chances again, but with
uncertainty in the strength and positioning of the ridge, timing and
precipitation amounts remain low confidence at this time.

&&

.AVIATION /14Z FRIDAY THROUGH TUESDAY/...
VFR conditions through most of the day, with high clouds
increasing this morning and mid clouds this afternoon.
Scattered showers and thunderstorms are expected to develop late
this afternoon and evening. Expect locally lower ceilings and
visibilities, lightning, and possibly some gusty winds to
accompany any stronger storms. The probability that a storm
will hit any particular port is low at this time so will use
prob30 to cover the convection threat. Activity should dissipate
with the loss of sunlight. Lower clouds are possible late
tonight.

.Outlook...
Restriction potential continue through Saturday, then again
early next week as multiple disturbances cross the region.

&&

.CLIMATE...
Some record highs may be approached on Friday as well as record
lows on Saturday. (* denotes current forecast temperature
exceeds value)

               5/3 Record High  Year
Pittsburgh          95          1887
Wheeling            90          1942
Morgantown          88          1965, 2012
New Philadelphia    89          2012
Zanesville          91          1938
Dubois              84          2012

               5/4 Record Low   Year
Pittsburgh          65          1938
Wheeling            63          1931, 1939, 1941
Morgantown          63          2021
New Philadelphia    60*         2012
Zanesville          65          1902
Dubois              N/A         N/A

&&

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

&&

$$

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