212
FXUS61 KPBZ 042239
AFDPBZ

Area Forecast Discussion
National Weather Service Pittsburgh PA
639 PM EDT Sat May 4 2024

.SYNOPSIS...
Intermittent rain and a few storms are possible through the
weekend. With clouds and rain, temperatures will be cooler
today, but will rebound Sunday as a southerly flow returns. A
brief break in the rain is possible Monday.

&&

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

- Showers slowly move across the area, thunderstorms in the
  afternoon.
- Cooler temperatures today.
-------------------------------------------------------------------

East coast ridge will move very little today and amplify this
morning in response to trough digging into the northern Plains.
We will continue to rest on the western side of the ridge where
a shortwave will drift northward throughout the day.

Deep moisture will flow northward on the backside of the ridge
axis keeping in plenty of clouds and the risk for showers all
day. An increasing southeasterly flow at the surface will pump
Atlantic moisture into the region aiding in the shower
development. For the most part, rainfall should be on the light
side. There are some deterministic models today that suggest a
1.40 PWAT leading to the 99th percentile in dealing with climo
PWATs. That said, the NBM only gives roughly 20% probability of
> 0.75 inches from 8am this morning through 2am tonight. Thus,
it will depend on where thunderstorms develop. Clouds, showers
and a cool easterly flow will keep temperatures slightly below
normal today.

Expect thunderstorms to dissipate by this evening but the shower
potential is expected to persist through tonight. This will keep
warmer temps around for the low.

&&

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

- Unsettled pattern remains with rain chances continuing on
  Sunday. Thunder possible on Sunday.
- Temperatures push back above normal Sunday and Monday.

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

East coast ridge will flatten and drift eastward on Sunday. The
shortwaves riding northward on the western flank of the ridge
will also shift to the east. Shower coverage looks to dissipate
Sunday morning. A weak cold front will slowly cross Ohio
Sunday. Models are hinting that scattered storms could develop
ahead of the front Sunday afternoon. The air mass during the
afternoon is certainly conditional and with any breaks in cloud
cover or WAA at the surface will be enough for convective
development. In fact, PWATS another day being in the 1.20 to
1.40 range with skinny CAPE will make for a heavy rainfall
threat. However, there are some dry layers in the model
soundings with DCAPE values between 400 J/Kg and 600J/Kg may
lead to a few strong storms with downburst potential. Temperatures
will warm on Sunday as the low-level flow veers to the
southwest ahead of the front which may be enough to kick start
the event tomorrow afternoon.

Ensembles have been consistent in showing a shortwave trough over
the Middle Ohio Valley approaching, but weakening, on Monday as it
interacts with a weak ridge over our region. A south-to-north
gradient in PoP values still seems appropriate for the
Monday/Monday night period. The pattern does continue to
coincide with development each day with day time heating.

&&

.LONG TERM /MONDAY NIGHT THROUGH SATURDAY/...
KEY MESSAGES:

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

Uncertainty still reigns after Monday. Most guidance depicts a
ridge centered over the Great Lakes at 12Z Tuesday, along with a
deep closed upper low in or near the Dakotas. The upper low
appears likely to fill during the midweek period, and as it does
so, shortwaves rotating around it appear to flatten out the
ridge as it moves across the Upper Ohio Valley, finally eroding
it almost completely in the northeast CONUS. Some strength and
timing issues remain with the details of this process, which in
turn could impact precipitation amounts and timing.

Nevertheless, a warm front is likely to cross on Tuesday as the
ridge progresses eastward. This will lead to the persistence of a
warm and moist airmass, with precipitable water values at or above
the 90th percentile in the climatology. Along with the previously
mentioned shortwave activity, this will keep an active weather
pattern in place for our region, with decent daily precipitation
chances through Friday. Deep-layer shear will increase as well
behind the departing ridge, so severe weather chances will need to
be monitored as well.  According to CSU machine-learning guidance
and NBM CWASP probabilities, Wednesday and Thursday may be the
days to watch.

Rain chances then continue to show additional activity on
Friday with the post frontal trough passing across the area.
There is little confidence on this occurrence though.

&&

.AVIATION /00Z SUNDAY THROUGH THURSDAY/...
Weak embedded shortwaves within broad southwest flow on the west
side of a ridge axis will continue to promote waves of showers
with low probability lightning through 15z Sunday. Coverage and
storm intensity will vary through that time, but it remains hard
to define the exact timing of the heavier rains and more
widespread coverage. Position of the region generally to the NE
of a weak surface low feature means area cigs will remain or
fall through the overnight hours, resulting in widespread
MVFR/IFR restrictions.

Modest height arises ahead of a more clearly defined wave
combined with diurnal heating will lift area cigs after 15z and
promote a brief lull in convective activity. Late day passage of
that shortwave and associated weak surface cold front will
create scattered thunderstorm coverage mainly after 21z.

.Outlook...
A moist boundary layer behind the frontal passage and evening
thunderstorms Sunday night likely will lead to widespread
MVFR/IFR restrictions. Some improvements are expected Monday
with influence of high pressure to the north, but shortwave
movement across the TN River Valley may maintain some
restriction/precipitation chances for southern terminals.

The rest of the week will remain active with varying periods of
precipitation and restrictions amid low pressure passage.

&&

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

&&

$$

SYNOPSIS...Shallenberger
NEAR TERM...Shallenberger
SHORT TERM...Shallenberger
LONG TERM...CL/Shallenberger
AVIATION...Frazier