606
FXUS61 KPBZ 221107
AFDPBZ

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

.SYNOPSIS...
Fog dissipates after sunrise, giving way to a seasonably hot
day. Precipitation chances and seasonable temperatures return
for Monday to Wednesday, with uncertainty increasing late-week.

&&

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

- Fog clears beyond sunrise.
- Seasonably hot weather today and warm overnight.
-------------------------------------------------------------------

Webcams, the night fog satellite difference, and observations
have given enough evidence of dense fog development,
particularly in areas that received rain in the last 24 hours,
for the issuance of a Dense Fog Advisory valid through 10am.
Coverage is most widespread surrounding Allegheny County to the
north, east, and south. It`s attempting to spread further west
toward the Pittsburgh metro but struggling with locally warmer
temperatures there. Expect this to be the case for the next
couple hours before visibility improves with onset of mixing
this morning.

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.
-------------------------------------------------------------------

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 /11Z SUNDAY THROUGH THURSDAY/...
Already beginning to see patchy dense fog developing over areas
that saw the most rain today, primarily along the higher terrain
and across northern WV. Visibilities at DUJ/FKL have dropped to
IFR or lower and LBE is down to MVFR to start the 06Z TAF period.
Expect the fog to gradually become more expansive and dense in
these areas through the rest of the night, with visibilities at
the aforementioned terminals (and at MGW) deteriorating through
sunrise. Dense fog is less likely farther west, though
PIT/AGC/HLG could still see a brief period at MVFR/IFR right
around sunrise. Fog should lift everywhere by 14Z, with VFR
conditions expected the remainder of the day under building
high pressure.

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

&&

.PBZ WATCHES/WARNINGS/ADVISORIES...
PA...Dense Fog Advisory until 10 AM EDT this morning for PAZ007>009-
     013>016-022-031-073>078.
OH...Dense Fog Advisory until 10 AM EDT this morning for OHZ069.
WV...Dense Fog Advisory until 10 AM EDT this morning for WVZ004-012-
     021-509>514.

&&

$$

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