-- Discussion containing changed information from previous version are highlighted. --
848
FXUS61 KPBZ 041142
AFDPBZ

Area Forecast Discussion
National Weather Service Pittsburgh PA
742 AM 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 /UNTIL 6 PM THIS EVENING/...
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KEY MESSAGES:

- Showers taper off overnight.
- Showers slowly move back over the region later this morning.
- Cooler temperatures today.
-------------------------------------------------------------------

The 730 AM update focused on an update to PoPs and weather grids
based on current radar trends. A small thunder chance was added
in near and southwest of Pittsburgh, where hi-res models show
some potential for 500-1000 J/kg of CAPE later today. Overall, the
forecast remains on track.

Previous discussion...

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. HREF probs for 24 hour rainfall ending at midnight tonight
for >0.25 generally range from 30 to 50% with some pockets of
60 to 70% over portions of northern WV and the higher
elevations.

Clouds, showers and a cool easterly flow will keep temperatures
slightly below normal today.
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&&

.SHORT TERM /6 PM THIS EVENING THROUGH MONDAY/...
KEY MESSAGES:

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

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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. However, ample cloud
cover,limited instability, and lack of upper level support
should work to shunt storm development and intensity.

Temperatures will warm on Sunday as the low-level flow veers to
the southwest ahead of the front.

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.

&&

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

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

&&

.AVIATION /11Z SATURDAY THROUGH WEDNESDAY/...
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Southeast wind this morning is keeping ceilings in the VFR range
for most terminals, save for FKL/DUJ north of I-80. Shower
coverage, currently confined to areas ast of PIT, will continue
to wane through the morning. Coverage is then expected to pick
up again after 18Z with diurnal heating. Locally lower ceilings
and visibilities can be expected in the heavier showers.
Continued to leave thunder out of the TAFs during that period
given uncertainty surrounding how much instability will develop.
If lightning does occur, the best chances according to hi-res
ensembles would be southwest of PIT, so a mention of thunder at
ZZV and HLG may be needed in future updates.

Any threat of thunder will end with sunset, but fairly
widespread shower activity is forecast to continue well into the
night. Ceiling restrictions will continue, with widespread
IFR/low MVFR ceilings forecast. Patchy drizzle/mist can also be
expected between any more sustained rain showers.


.Outlook...
Restriction potential continues through Sunday morning, with
additional storm chances Sunday afternoon. Periodic restrictions
may continue through early next week as multiple disturbances
pass through the region.
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&&

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

&&

$$

SYNOPSIS...22
NEAR TERM...22/CL
SHORT TERM...22/CL
LONG TERM...CL
AVIATION...Rackley/CL