-- Discussion containing changed information from previous version are highlighted. --
158
FXUS61 KPBZ 222352
AFDPBZ

Area Forecast Discussion
National Weather Service Pittsburgh PA
752 PM EDT Sun Sep 22 2024

.SYNOPSIS...
Precipitation chances and cooler temperatures return Monday and
continue through the week, though uncertainty increases by
late-week.

&&

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

- Rain chances return tonight
-------------------------------------------------------------------

Shortwave ridging will maintain generally dry weather through
this evening. The ridge will shift eastward by late evening.

A shortwave trough, and its associated surface cold front, were
currently across the Midwest region. This trough will track
eastward, and cross the Upper Ohio Valley region late
tonight/early Monday. Initially, mid and high clouds will
increase through the evening ahead of the trough. Rain chances
will increase as moisture and ascent move across the region. 12
hour 500mb height falls of 30 meters were observed across the
Midwest with this trough.

Given the increase in cloud coverage and light wind prevailing
overnight, fog development will be mostly held in check. Lows
will be some 10-15 degrees above average with weak warm
advection and subpar radiational cooling.

&&

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

- Rain chances continue through mid-week.
- Temperatures dip back down closer to normal.
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Clustered ensembles all depict an upper trough establishing across
the central CONUS with various flavors of depth likely tied into
rounds of lows moving through its base. The first low will track
across southern Michigan very early Monday morning, and this will be
the first of several rounds that will bring continued rain chances
through this week. As the doors open to allow an influx of Gulf
moisture, ensemble mean precipitable water values bump up to 1.5-
1.7" come Monday which is well above climatology for this time of
year. Most likely onset timing of rain is after midnight or so for
eastern Ohio and 4am for western Pennsylvania with showers
continuing through the day. Probabilities of exceeding 0.5" through
Monday night sit around 30-50%.

The second low will arrive on Tuesday and indications are that it
will be stronger than Monday`s with a more amplified troughing
pattern digging. Most likely track is to our west and probabilities
for higher totals are evident on Tuesday via spreads in 24 hour QPF.
This is likely a result of the possibility for a strip of enhanced
convergence resulting in potentially locally higher rainfall totals.
Where this may set up is still a bit fuzzy, but will have to monitor
the potential. The distribution of storm total rainfall through
Wednesday morning is between 0.5" and 1.5" areawide with a tail
toward higher values highlighting the potential for locally greater
amounts.

Temperatures through mid-week will be cooler owing to increased
cloud coverage and precipitation.

&&

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

- Uncertainty increases greatly for the latter half of the week with
  potential tropical low interaction.
- Rain chances will continue through the end of the week.
-------------------------------------------------------------------

A weak boundary may pass through the area sometime Wednesday into
Thursday, but seeing significant spread in the ensembles on the
timing which will impact when we lose the rain chances. The central
CONUS trough digs deeper on Wednesday and potentially gets cut off
form a northern stream trough, but ensemble clusters exhibit
quite a bit of disagreement here. A faster solution cuts off
rain chances overnight Wednesday night while others suggest a
slower progression and maintain the rain all the way through
Thursday night. Meanwhile, the remnants of a potential tropical
system in the Gulf may interact with the trough.

At this time, the highest probability scenario is that the northern
stream trough is through by late week and the main QPF swath
affiliated with the remnant system is through the mid-Atlantic. A
few ensembles still lag the passage, with some higher QPF totals
possible across the southeastern half of the forecast area. Another
cluster of ensembles has the system moving into the Midwest behind
the trough. Will stick with NBM for now given all of the
uncertainty, but the mean with this setup is likely not the most
realistic outcome. This will warrant watching for the late-week
period.

All told, the greatest membership from the ensemble total
accumulated precipitation through Friday night is distributed
between the 1"-2.5" range, though again scenarios exist for
higher amounts with a respectable membership exceeding 2.5". So,
we will continue the "wait and see" pattern until guidance
starts suggesting one solution is favored.

&&

.AVIATION /00Z MONDAY THROUGH FRIDAY/...
-- Changed Discussion --
Lower clouds and light rain is already moving into eastern Ohio
this evening in advance of a cold front and associated low
pressure. Initial rain will be very light given dry low-levels,
and showers will continue to break up as they cross into western
PA. Better rain coverage is then expected overnight into Monday
morning, with ceilings dropping into MVFR/IFR areawide near
sunrise. The best chance for IFR cigs remains at FKL/DUJ. Rain
chances will decrease after 12z, but lower probability showers
may continue through the morning. Have covered this with PROB30s
for some terminals. Ceiling improvement is expected in the
afternoon as rain clears, though this will be temporary as
clouds lower once again Monday night.


.Outlook...
Rain and restriction chance continues into Tuesday with another
low pressure center. Unsettled weather is then possible through
mid-week.
-- End Changed Discussion --

&&

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

&&

$$

SYNOPSIS...MLB/Milcarek
NEAR TERM...WM/MLB
SHORT TERM...MLB/Milcarek
LONG TERM...MLB/Milcarek
AVIATION...Rackley