PBZ issues Area Forecast Discussion (AFD) at Dec 22, 7:35 PM EST315
FXUS61 KPBZ 230035
AFDPBZ
Area Forecast Discussion
National Weather Service Pittsburgh PA
735 PM EST Sun Dec 22 2024
.SYNOPSIS...
Dry weather continues with the next chance of precipitation
Monday night into Tuesday morning. Temperatures will begin a
moderating trend into the coming week.
&&
.NEAR TERM /THROUGH MONDAY/...
KEY MESSAGES:
- Dry under high pressure.
- Cold with highs in the 20s and overnight lows in the teens.
--------------------------------------------------------------------.
High pressure has resulted in a clear sky across the Upper Ohio
Valley this evening. Warm advection and southwest flow aloft
will likely push some high and eventually middle cloud cover
into the region overnight, especially towards morning. This may
keep temperatures from dropping as far as they could in the
nearly calm conditions. Ended up nudging overnight low upward
slightly, but given the dry dewpoints and light wind, still
leaned toward the cooler side of the guidance envelope.
&&
.SHORT TERM /MONDAY NIGHT THROUGH TUESDAY NIGHT/...
KEY MESSAGES:
- Light precipitation returns Monday night with some
snow accumulation possible north and east of Pittsburgh.
- Warmer on Christmas Eve with afternoon highs challenging the
chances of a white Christmas.
--------------------------------------------------------------------
Most of the daytime hours on Monday are likely to be dry with the
influence of departing high pressure. Ensembles are in
respectably good agreement on the progression of a trough
crossing the area Monday night into Tuesday morning with little
deviation on its strength or timing lending higher confidence. A
weak attendant surface low will track east across the Great
Lakes pulling a weak boundary through as it passes by.
Precipitation probabilities are high at 80%+ with this feature,
but moisture return ahead of it appears paltry given a lacking
meridional component to the flow ahead of its arrival.
Precipitable water values only have around a 50-60% chance of
exceeding 0.5". That said, with the timing being in the
overnight hours, probability of dominant precip type to be snow
is highest north and east of Pittsburgh coincident with the
colder air where overnight lows <32F are 80-100% (30-50% in the
urban areas). Probability of total liquid >0.10" is as high as
60-70% north of Pittsburgh closer to the best forcing. In terms
of snow, NBM probability for 1" is up to about 60% concentrated
in Forest, Clarion, and Jefferson Counties; the reasonable high
end of the goal posts sits at around 3" at this point with the
low end <1", so there's still some uncertainty in amounts, but
generally are favoring the 1-3" range. Elsewhere, rain or a
rain/snow mix are more likely given the warmer temperatures.
If at least 1" of snow does fall overnight and provide at least that
much snow depth headed into the day on Christmas Eve, we're looking
at a high probability for afternoon highs to exceed the freezing
mark, so snow depth may be challenged as could a White Christmas (1"
of snow on the ground at 7am on Christmas Day). A transition to rain
showers then becomes more likely on Tuesday with lingering moisture
and shortwave passages as the trough exits, but additional
measurable rain chances are only peaking around 50%.
&&
.LONG TERM /WEDNESDAY THROUGH SUNDAY/...
KEY MESSAGES:
- Low precipitation chances on Christmas Day.
- Warming trend through the end of the week.
- Uncertainty in the pattern by next weekend.
--------------------------------------------------------------------
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, but this is only represented by one ensemble cluster while the
others suggest higher heights. This would be a non-trivial solution
though should it come to fruition and provide greater moisture
return in a bit more amplified flow compared to other solutions that
suggest only low-end probability scattered rain showers. If precip
does occur, profiles aren't favorable for snow with probability near
100% to exceed 32 degrees for highs.
For the latter half of the week, all clusters suggest building
ridging by Thursday, again save one solution that hangs back the
upper disturbance and associated precipitation chances into early
Thursday morning. Regardless, ridging will finally take hold with
570+ dam heights presenting as increasing probability. Deep layer
southerly component flow will support a warming and moistening trend
as highs rise above 50 degrees south of Pittsburgh with a 40-60%
chance on Thursday and incrementally stepping up further north
into the weekend. Confidence in a warming trend is increasing.
Another disturbance is possible come next weekend, but deviance
from the grand ensemble solution increases substantially in
regard to precipitation chances.
&&
.AVIATION /01Z MONDAY THROUGH FRIDAY/...
High pressure overnight will lead to calm to light southeast
winds with mostly clear skies. Tomorrow, the pressure gradient
will increase slightly, ushering in southerly flow. Gusts likely
the highest at ZZV and HLG up to 20kts, decreasing to the east. High
confidence in VFR through the TAF period save after 00Z Tuesday
with increasing chances of cig falls and rain snow.
Outlook...
A system will move through tomorrow night, most likely between
00Z and 06Z that will allow a burst or moderate to heavy rain
and snow. Snow is favored for FKL, DUJ, and BVI for now with
rain and mix chances increasing to the south. Moderate forcing
suggests snowfall rates could be heavy and brief as a front
crosses through, with 0.5" to 1" per hour rates in a 1 to 3
hour window. IFR is likely where the heaviest snow ends up with
LIFR possible, visibilities will increase in mix and rain.
After the passage, lowering cigs and continued restrictions are
forecast. Non-zero restriction chances persist through mid-
week.
&&
.PBZ WATCHES/WARNINGS/ADVISORIES...
PA...None.
OH...None.
WV...None.
&&
$$
SYNOPSIS...88
NEAR TERM...CL
SHORT TERM...MLB/88
LONG TERM...MLB/88
AVIATION...Milcarek
Source:
PBZ issues Area Forecast Discussion (AFD) at Dec 22, 7:35 PM EST---------------
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