PBZ issues Area Forecast Discussion (AFD) at Dec 23, 4:23 PM EST308
FXUS61 KPBZ 232123
AFDPBZ
Area Forecast Discussion
National Weather Service Pittsburgh PA
423 PM EST Mon Dec 23 2024
.SYNOPSIS...
A quick hitting system brings rain and snow to the area
overnight Monday night with snow accumulation north of
Pittsburgh and a freezing rain threat to the West Virginia
ridges on Tuesday. Temperatures moderate for the remainder of
the week with a slight chance of rain on Christmas Day.
&&
.NEAR TERM /THROUGH TUESDAY/...
KEY MESSAGES:
- Quick shot of precipitation returns tonight with accumulating
snow in the I-80 corridor and ridges.
- Rain or rain/snow mix more likely elsewhere.
--------------------------------------------------------------------
Low pressure attendant to a compact-but-strong shortwave trough
will advance across the region tonight. Strong warm advection
ahead of the sfc low pressure has yielded temps broadly in the
40s for much of the region south of Pittsburgh, with thickening
clouds limiting temperature recovery to the north. Temperature
nevertheless is at or above freezing almost everywhere, but
exceptionally dry, as dewpoints remain in the low-mid teens.
This dry boundary layer means precipitation onset will be
delayed as the column will need to saturate from above, but also
means wet-bulb effect will quickly reduce temperature when it
does.
As the shortwave trough approaches late this evening, strong,
focused ascent will spread from the I-80 corridor sewd across
the region, leading to a brief (few-hour) period of heavy
precipitation rate. With the thermal profile expected with high
(near 100%) confidence to be below freezing, this precipitation
in the I-80 corridor is likely to be all snow. HREF probability
of snowfall rate > 0.5"/hr is near 100%, which means snow will
fall fast enough to accumulate even on above-freezing road
surfaces. An advisory was issued for overnight tonight to
highlight this snow impact, with totals as high as 2-3" within
this axis from Mercer to Indiana and adjacent counties.
In the ridges, a brief burst of snow is possible early Tue
morning, but dry air aloft in the wake of the shortwave trough
will erode ice nucleation, leading to a stagnant and saturated
deep low-level airmass. This combination is a recipe for
freezing drizzle, which could last for the better part of Tue in
the ridges. The existing advisory was expanded nwd to include
Westmoreland and Fayette ridge zones.
Outside of the ridges, any wintry impact should erode quickly
by morning, with modest cloud breaks leading to above-freezing
temperature as limited heating occurs.
&&
.SHORT TERM /TUESDAY NIGHT THROUGH WEDNESDAY NIGHT/...
KEY MESSAGES:
- Low precipitation chances on Christmas Day.
--------------------------------------------------------------------
Some melting is certainly probable during the day on Christmas
Eve. Snow depth thus may be challenged, as could a white
Christmas (1" of snow on the ground at 7am on Christmas Day).
The highest chance of achieving a white Christmas will be for
those who have the most snow on the ground from this past
weekend's event and what falls tonight.
In the wake of the Christmas Eve disturbance, ensembles converge on
a brief ridging solution downstream of another quickly approaching
trough across the Midwest, that is favored to weaken and
flatten out as it approaches locally on Christmas Day. Some
uncertainty comes into play with potential phasing of a northern
stream wave traversing north of the Great Lakes with the
weakening southern wave which also presents a quicker arrival of
the impulse, but this is not a likely outcome among ensemble
clusters, and the most likely scenario suggests higher heights
and prolonged ridge presence.
Should the less-likely outcome prevail, it would be a non-
trivial outcome, providing greater moisture return in a more-
amplified flow pattern compared to other solutions, that
suggest only very-low-end probability of rain showers in
ern OH. For now, the more likely outcome favors the drier
solution. If precip does occur, profiles aren't favorable for
snow with probability near 100% to exceed 32F maxima.
&&
.LONG TERM /THURSDAY THROUGH MONDAY/...
KEY MESSAGES:
- Warming trend through the end of the week.
- Uncertainty in the pattern by next weekend.
--------------------------------------------------------------------
For the latter half of the week, all clusters suggest building
ridging by Thursday, again save one solution that slower
progression of a shortwave trough and holds associated
precipitation chances into early Thu morning.
Regardless, ridging will finally take hold with 570+ dam
heights increasing in likelihood. Deep-layer sly component to
the flow will support a warming and moistening trend as highs
sneak up to the 50 degree mark south of Pittsburgh with 40-60%
chance on Friday and incrementally stepping up farther north
into the weekend. Confidence in a warming trend is increasing.
Another shortwave trough is possible over the weekend, but
significant uncertainties continue in the pattern evolution.
What can be said with relative confidence is that there is
potential for a warm weekend, and a high likelihood of rain at
some point during the weekend (Sat/Sun timeframe).
&&
.AVIATION /20Z MONDAY THROUGH SATURDAY/...
VFR conditions and south winds around 7-10 knots continue
through the rest of the afternoon at all terminals. Increasing
cirrus clouds moving in from the west gradually lower late this
evening to low-end VFR ahead of an approaching disturbance. A
quick round of snow moves through overnight from the northwest,
reaching FKL/ZZV around 03Z, PIT/AGC around 05Z, and MGW by
around 08Z. A quick deterioration to high IFR/low MVFR is
anticipated once precip begins. Low-end IFR or even LIFR will
be possible north of PIT where snow is also most likely to be
the dominant precip type. Southern terminals, from PIT south,
are more likely to see a rain/snow mix, while ZZV may remain
all rain. Precipitation departs to the east by or shortly after
pre-dawn hours Tuesday, around 09Z for FKL/ZZV and later for
terminals farther south and east. The exception is LBE/MGW/DUJ
where weak upslope could promote lingering drizzle or light rain
into the day Tuesday.
Outlook...
Restrictions, predominantly in the form of low ceilings, are
likely to linger from the end of the current TAF period through
at least Tuesday night. Ensemble guidance indicates a 60% or
greater probability of MVFR at all terminals during that time,
though IFR probabilities drop to 20% or lower.
Improvement to VFR will be possible Wednesday, when guidance
indicates probabilities for MVFR ceilings finally drop to 20
percent or lower at all terminals. Any improvement would be
short-lived, however, as probabilities rebound to the 30-50%
range (especially north of PIT) Wednesday night into Thursday.
&&
.PBZ WATCHES/WARNINGS/ADVISORIES...
PA...Winter Weather Advisory from 9 PM this evening to 5 AM EST
Tuesday for PAZ007>009-014>016-022-077-078.
Winter Weather Advisory from 4 AM to 7 PM EST Tuesday for
PAZ074-076.
OH...None.
WV...Winter Weather Advisory from 4 AM to 7 PM EST Tuesday for
WVZ511>514.
&&
$$
SYNOPSIS...Kramar/MLB
NEAR TERM...Kramar/MLB
SHORT TERM...MLB/Kramar
LONG TERM...MLB/Kramar
AVIATION...Cermak/22
Source:
PBZ issues Area Forecast Discussion (AFD) at Dec 23, 4:23 PM EST---------------
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