083
FXUS61 KPBZ 081824
AFDPBZ

Area Forecast Discussion
National Weather Service Pittsburgh PA
124 PM EST Fri Nov 8 2024

.SYNOPSIS...
Dry weather is expected through Saturday. Low pressure will
support widespread rainfall Sunday into Monday. Uncertainty
increase into next week with possible rain chances returning by
mid-week.

&&

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

- Gusty wind this afternoon with a passing dry cold front.
- Elevated fire danger today.
- Overnight lows right around normal.
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A picturesque late fall day underway with sunny skies across
the area this afternoon and very dry air overhead. A weak
surface trough will move through our region from north to south
during the afternoon, but will have little to no moisture to
work with, so its passage will be dry with no effect to sensible
weather aside from increasing wind gusts. The pressure gradient
will tighten ahead of it, and with deepening mixing heights,
gusty wind is expected this afternoon with ensemble probability
for >25 mph at 40-70%. The deep mixing will also drop dew
points to the mid 30s resulting in minimum RH values down as low
as 30%. This will again raise concerns for fire weather with
antecedent dry conditions. In coordination with state officials
and surrounding offices, have issued an SPS through this evening
for most of southwestern Pennsylvania where the best overlap of
minRH values and wind gusts is expected. Higher RH values
further northwest will preclude greater fire weather concerns.

With ample sunshine and no cold advection until late in the
day, high temperatures will be close to 10 degrees above normal;
areas south of Pittsburgh have a 40-60% shot of breaking 65F
highs while elsewhere low 60s are most favored.

Cold advection aloft in northwest flow behind the trough likely
develops a stratocu deck for part of the overnight hours, but
as advection becomes more neutral in the latter half of the
night, should see cloud coverage erode and hi res ensemble
spread depicts this nicely with the higher end of the
distribution envelope signaling a return of partly cloudy to
mostly clear skies.

&&

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

- Dry start to the weekend with above-normal temperatures.
- High confidence in widespread wetting rainfall on Sunday.
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Upper ridge axis shifts overhead on Saturday and amplifies
downstream of a closed low across the Plains. Warm advection aloft
with the building ridge atop easterly surface wind will push 850 mb
temperatures to 8-12C, higher southwest and lower northeast, which
will push highs again a couple degrees above normal. Still dry low
levels and localized downsloping effects off of the ridges will
allow for dew points to mix out again in the afternoon and minRH
values down to the upper 20/low 30 percent range. Lesser wind
gusts should preclude widespread fire weather concerns, but
conditions will warrant monitoring. Clouds increase late
Saturday as deep layer moisture ramps up ahead of approaching
low pressure. Warm advection will keep overnight lows in the
upper 30s-low 40s.

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 60-80% 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 FRIDAY/...
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.
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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.

&&

.AVIATION /18Z FRIDAY THROUGH WEDNESDAY/...
VFR expected today with winds out of the WNW with gusting to
around 20kt during the afternoon as high pressure builds over
the Great Lakes and the pressure gradient increases.

.Outlook...
VFR is expected Saturday, before rain and restrictions
overspread the region Saturday night and Sunday with low
pressure. VFR returns Monday and Tuesday under high pressure.

&&

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

&&

$$

SYNOPSIS...MLB
NEAR TERM...MLB
SHORT TERM...MLB
LONG TERM...MLB
AVIATION...88