131
FXUS61 KPBZ 092321
AFDPBZ

Area Forecast Discussion
National Weather Service Pittsburgh PA
621 PM EST Sat Nov 9 2024

.SYNOPSIS...
Dry weather will continue before low pressure brings widespread
rainfall Sunday into Monday. Uncertainty increase into next
week with possible rain chances returning by mid-week.

&&

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

- Increasing clouds tonight; rain may arrive in eastern Ohio
  before sunrise.
- Overnight temperatures remain a bit above normal.
-------------------------------------------------------------------

Made generally minor adjustments to the forecast tonight, mainly
focused on dewpoints and sky cover. Easterly flow and a very dry
column are supported low dewpoints and relative humidity levels
in the 20 to 30 percent range across the CWA, with locally drier
values. Temperatures in the upper 50s/lower 60s currently
represent above-normal values. Southwest flow aloft behind
departing high pressure will continue to help thicken mid and
upper-level clouds this evening.


Warm advection will keep overnight lows in the upper 30s-low
40s. A warm frontal boundary will lift towards the Upper Ohio
Valley tonight ahead of Upper Midwest low pressure. Increasing
isentropic lift and precipitable water will continue to thicken
cloud cover, but high condensation pressure deficits/antecedent
dry air will generally keep any precipitation from arriving in
our eastern Ohio counties until after 09Z or so.

&&

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

- High confidence in widespread wetting rainfall on Sunday.
-------------------------------------------------------------------

Deep southwest flow will provide a strong pull of Gulf and
remnant Rafael moisture on Sunday with integrated vapor
transport values 2-4 SD above normal and ensemble mean
precipitable water near 1.3" which is near the daily maximum
value. As low pressure lifts through the Great Lakes region,
widespread rainfall is expected to arrive in the morning hours.

The most steady rain likely comes Sunday afternoon as an 850 mb
jet encroaches and enhances low level convergence. Current
ensemble probability for a wetting rain (at least 0.10") is very
high at 95-100% areawide. Similarly, at least 0.25" is 90+%
with a 60-75% chance of a half an inch. The higher end (90th
percentile) of the goal posts has continued to sit around an
inch and is likely contingent on capitalization of whatever
marginal instability can develop; instability likely won`t be
surface-based given the low-level warm advection regime, so any
severe weather threat is low. The system will be progressive
overall, but wouldn`t rule out some localized totals nearer to
the 75th-90th percentile in some of the maximized higher
rainfall rates.

&&

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

- Low confidence rain chances for the beginning of the week.
- Better rain chances come mid-week but still some uncertainty.-
- Highs a few degrees above normal.
-------------------------------------------------------------------

Some showers may linger into Monday behind departing low pressure as
a weak secondary trough moves through, but ensemble clusters suggest
increasing uncertainty with the upper level pattern to start out
next week as an additional upper wave follows quickly behind the
original one from Sunday. Some clusters merge these waves while
others favor a flatter, more progressive pattern. A slower departure
would favor cooler temperatures and lingering precip chances through
Monday night while a faster pattern favors warmer, drier conditions.

Overall consensus is that high pressure and upper ridging briefly
return which favors still above normal temperatures through mid-
week. Another better chance for rain may come sometime Wednesday
into Thursday with another round of low pressure, but significant
differences among the ensembles suggests a low confidence forecast
by this point. Therefore, it is likely that given the drier
trend, Friday will likely see high pressure and dry conditions
returning.

&&

.AVIATION /00Z SUNDAY THROUGH THURSDAY/...
SCT to BKN upper level cloud deck, with upstream base height
observations between 150-200, will push into the area tonight as
moisture increases ahead of approaching low pressure that will
bring widespread rain and restrictions on Sunday.

Cloud bases lower further into the morning hours on Saturday and
restrictions are favored to overspread the region coincident
with precipitation as low level saturation is achieved. Latest
ensemble probability indicates most likely arrival time of
showers and MVFR CIG/VIS in rain around 12z at ZZV, 15z at PIT,
and 17z at LBE. Much of the uncertainty in onset time is
confined to +/- 1-2 hours of the forecast at this point.

MVFR conditions are high probability (90+%) with a 50-70%
chance of both IFR CIG and VIS as a low level jet aids in
forcing and more moderate rain, but timing of this is currently
just encompassed at the end of the PIT TAF period. Visibility
and ceilings will improve some headed into the overnight hours
Sunday night, but lingering low- level moisture overnight
doesn`t bode very well for a high confidence return to VFR.

.Outlook...
A passing cold front early Monday will decrease the potential
for rain. However, restrictions may linger into late Monday
morning due to residual low-level moisture and cold advection.

&&

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

&&

$$

SYNOPSIS...88
NEAR TERM...CL
SHORT TERM...CL/88
LONG TERM...88
AVIATION...MLB/Milcarek