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000
FXUS61 KPBZ 142132
AFDPBZ

Area Forecast Discussion
National Weather Service Pittsburgh PA
532 PM EDT Sun Apr 14 2024

.SYNOPSIS...
Thunderstorm chances increase again on Sunday with a cold
front, some potentially strong to severe. A brief bout of dry
weather expected Monday before rain chances return on Tuesday
with moderating temperatures into next week.

&&

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

- Thunderstorm chances return today with potential for strong to severe
  with a large portion of the area outlined in an Enhanced Risk
  (3/5) for severe weather.
- A Marginal Risk (1/5) is in place for excessive rainfall today.
-----------------------------------------------------------------

508 PM Mesoscale update... Severe Thunderstorm Watch has been
issued for much of the area through 10pm. Convection has rapidly
intensified in a more favorable environment south of Lake Erie,
with CAP 1500 j/kg and 45 kt effective bulk shear. Severe
thunderstorm warnings have begun along the line, with damaging
wind and large hail currently the main hazards.

359 PM Mesoscale update...
Convection was developing across Lake Erie. This should track
SEWD across the region late this afternoon and evening. Mixing
has dropped dew points into the 40s across much of the area,
though some recovery is expected ahead of the front. This lack
of low level moisture will be a limiting factor in tornado
development, though sufficient shear is in place. A band of
1000-1500 J/KG surface based CAPE was seen on mesoanalysis.
Expect the convection to intensity as it moves south off of the
lake.

The latest 18Z special sounding from PIT shows a mid level cap
in place. Some mid level cooling is expected in advance of the
front, and this should also allow for thunderstorm development.
Favorable downdraft CAPE is in place (600-900 j/kg) for damaging
wind gusts.

Previous discussion...
A belt of 40-50 knot westerly low level flow atop southwest
flow at the surface will support directional shear in the lowest
1-3 km, also the layer where the majority of shear and
clockwise curvature noted in hodographs will be confined to. Hi
res ensemble joint probabilities suggest the highest probability
of 60-90% for SBCAPE >1000 J/kg and deep layer shear >30 kt
setting up across western PA and into eastern OH. This
environment will be supportive of all hazards including damaging
wind, large hail, and tornado potential. While the environment
will be supportive of supercellular structures, the mean layer
flow will have a dominant west-east component along a similarly
oriented cold front which may make it more difficult for these
storms to propagate off of the initiating boundary and become
discrete, rather favoring more of a linear cluster type mode
with embedded supercells. Some question will come into play with
warm advection occurring aloft that may mute low level lapse
rates some as well as how far south the storms can sag before we
lose daytime heating. Any shower or thunderstorm development
should hold off until after 19-20z when latest CAMs initiate
convection north of I-80 and intensify and tracking south
through the evening with most likely arrival time to Pittsburgh
after 23z.

Mean precipitable water values will rise up to around 1" and, while
the front and convection should be progressive, still can`t rule out
localized flooding concerns given the saturated soils and parallel
component to the front promoting upscale growth. The latest HREF
favors highest precipitation rates and totals toward the PA ridges
with a 40-50% chance of exceeding 1" of rain. WPC has outlined the
area in a Marginal Risk (1/5) for excessive rainfall.

Convection should clear south of the area after 06-07z and give
way to generally cloudy skies overnight with lows not taking too
much of a hit in the wake of the boundary in the upper 50s
south of I-70 with upper 40s/lower 50s further north.

&&

.SHORT TERM /6 AM MONDAY MORNING THROUGH TUESDAY NIGHT/...
KEY MESSAGES:

- Dry weather returns Monday with moderating temperatures.
- Rain chances return for the latter half of Tuesday.
-------------------------------------------------------------------

With the only minimal uncertainty being driven by the progression of
the upper trough into Monday, confidence is high that the cold front
will clear the area by Monday morning and, aside from some low
probability shower chances south of I-70, the day should otherwise
be dry. Ensembles aren`t very bullish on a notable push of colder
air in the wake of the front as an 850 mb ridge quickly builds
counteracting weak cold advection in residual northwest flow; most
of the day should feature a rather sunny sky with increasing
subsidence drying out the boundary layer and temperatures are
expected to remain above normal with still a 70-90% chance of
exceeding 70 degrees mainly south of I-80.

Brief upper ridging slides overhead on Tuesday reinforcing the dry
weather for the first half of the day, but clouds increase from the
southwest with increasing moisture aloft ahead of an approaching
shortwave traversing and flattening the ridge and reintroducing
showers for the second half of the day. We should see a brief break
overnight Tuesday night before trailing low pressure arrives.
Amounts with this batch look light with even NBM 90th percentile
values only near 0.1-0.2" through Wednesday morning.

&&

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

- Temperatures remain above average.
- Rain chances continue into mid-week.
- Temperatures return closer to normal by the end of the week.
-------------------------------------------------------------------

Above normal temperatures and rain chances continue to be the theme
into mid-week as southerly return flow promotes warm advection
kicking highs above average with ensemble probability for >70F in
excess of 70% through Thursday.

What`s left of the ridging breaks down into Wednesday as an upper
trough and surface low pressure dig across the Midwest with
diffluent flow aloft promoting broad ascent. Primary ensemble
uncertainty stems from the progression of the trough and surface
low, but consensus tracks it through the Great Lakes to our north as
it occludes and returns rain to our region by Tuesday with a leading
shortwave passing through. Rain chances continue into Thursday as
the warm front approaches with the cold front following behind as
early as Wednesday night or more likely more toward early Thursday
morning. We`ll dry out briefly behind the front, but ensembles push
a secondary reinforcing trough through by late week which then
favors temperatures dipping back down towards normal to close out
the week and low confidence rain chances as early as Friday morning,
but more likely into Friday afternoon and evening. Still early
to talk rainfall totals, but ensemble spread sits from 0.2" on
the reasonable low end to near 1" on the high end through
Friday.

&&

.AVIATION /22Z SUNDAY THROUGH FRIDAY/...
A line of strong to severe thunderstorms will track SEWD across
the region through early this evening. This activity is faster
than recent model output. Timed these storms into the airports
using extrapolation. Strong wind gusts and large hail are the
main hazards with this line. Expect IFR conditions as well as
this line crosses.

General VFR is expected behind the front as high pressure
gradually builds over the region. Mixing has resulted in strong
wind gusts today, and these should also gradually diminish
through this evening after the storms end.

.Outlook...
VFR is expected under high pressure Monday and most of Tuesday.
Restriction potential returns late Tuesday and Wednesday with
approaching low pressure. Restrictions are possible into
Thursday under a subsequent upper trough.

&&

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

&&

$$

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