546
FXUS61 KPBZ 221411
AFDPBZ

Area Forecast Discussion
National Weather Service Pittsburgh PA
1011 AM EDT Sun Sep 22 2024

.SYNOPSIS...
A seasonably warm and dry day expected Sunday. Precipitation
chances and seasonable temperatures return for Monday to
Wednesday, with uncertainty increasing late-week.

&&

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

- Seasonably warm weather today and overnight.
- High clouds increase late.
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Webcams and observations have shown overall improvement in
visibility so the dense fog advisory has been allowed to expire
at 10am. Some localized areas around the I-80 corridor and
north are still seeing reductions to a half a mile or so, but
don`t anticipate this lasting much longer with daytime heating
and wind picking up.

A brief bout of upper ridging fills in behind the shortwave,
allowing high temperatures today to climb 10 to 15 degrees above
normal with mixing. Mixing in subsidence will also allow
relative humidities to drop into the 20s and 30s for spots. The
record high of 92F (2017) in New Philadelphia may be challenged.
High clouds are expected to increase throughout the day and
into the overnight as the next disturbance approaches.

Clouds and light winds are expected to limit fog mentions
tonight. The insulating effects of cloud cover will keep low
temperatures 10 to 15 degrees above average.

&&

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

- Rain chances prevail.
-------------------------------------------------------------------

Guidance is in good agreement that the aforementioned ridge
will move east and give way to quasi-zonal flow downstream of a
digging central CONUS trough. Through the short term, there is
good agreement that this trough will translate east, putting our
area in a region synoptically favored for low tracks and
precipitation.

By Monday, a trough of low pressure will sag from the lower
Great lakes to the Ozarks, with ample moisture pull from the
Gulf of Mexico ahead of it. This may push PWATs into the 1.5" to
1.75" range. This is near the 90th percentile of sounding
climatology for this time of year.

The first of many subtle lows riding the trough axis is expected
to arrive by Monday morning, though chances of exceeding 0.5"
remain around 20% to 30% for eastern Ohio and 30% to 50%
elsewhere, highest for the ridges. The second low is favored to
be slightly stronger, tracking our way Tuesday, but low track
and character will determine QPF amounts with the second round.
It is possible that there is a narrow convergence corridor that
could set up along a stagnant frontal zone, alluding to a low
threat of excessive rainfall. So far the storm total range
through 8am Wednesday is anywhere between around 0.5" and 2"
area wide with localized higher amount possible; a majority of
the distribution is swayed towards solutions exceeding 1" of
QPF.

&&

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

- Uncertainty increases in rainfall pattern as a tropical low
  interacts with the trough.
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The front may be slower to pass into the Wednesday and Thursday
timeframe, allowing for continued rain chances, though there are
considerable timing uncertainties with the passage. A majority
of ensemble members have the trough through by Wednesday night,
but some lag through Thursday night. The faster the trough
passes, the faster the cut-off of rain chances late week.

This will also become increasingly important as this trough may
pick up a tropical low. The highest probability scenario is that
the trough is through by late week and the main QPF swath
affiliated with the system is through the mid- Atlantic, though
a few ensembles lag the passage, with some higher QPF totals
possible across the southeastern half of the forecast area.
Another cluster of ensembles have the system moving into the
midwest behind the trough. This will warrant watching for the
late- week period.

Because of ensemble spread, the 10th, 25th, 50th, 75th, and 90th
percentiles of QPF are as follows: 0", 0.1", 0.2"-0.5",
0.5"-1.25", and 1.5"-3.0" (highest southeast of Pittsburgh).
So, we will continue the "wait and see" pattern to see if
guidance starts suggesting one solution is favored.

&&

.AVIATION /14Z SUNDAY THROUGH THURSDAY/...
Patchy dense fog/low stratus is impacting mainly terminals east
of PIT this morning. AGC, LBE, MGW, FKL, and DUJ are most
significantly impacted. PIT, HLG, and ZZV have escaped it -
generally due to the lack of rain at these latter terminals.
LIFR/VLIFR conditions will begin to improve between 13Z and 14Z,
with a return to VFR areawide by 15Z once daytime heating
commences. VFR and a light south/southwest wind will then
continue into the evening hours under upper ridging.

Clouds will thicken and lower tonight ahead of an advancing cold
front. Rain may then begin to spread into the region, starting
at ZZV around 06Z, where MVFR restrictions are possible by
sunrise.

.Outlook...
Rain and restriction chance increase into Monday with another
crossing cold front. Unsettled weather is then possible through
mid-week.

&&

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

&&

$$

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