PBZ issues Area Forecast Discussion (AFD) at Dec 24, 5:46 PM EST220
FXUS61 KPBZ 242246
AFDPBZ
Area Forecast Discussion
National Weather Service Pittsburgh PA
546 PM EST Tue Dec 24 2024
.SYNOPSIS...
Dry weather returns for most through the remainder of the week
aside from lingering light snow and freezing rain in the ridges
through Tuesday afternoon. Temperatures begin to moderate on
Christmas and continue to warm through the weekend with another
round of rain returning on Saturday.
&&
.NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...
KEY MESSAGES:
- Dry but cloudy for most of the area through tonight.
- Threat for light snow or freezing rain in the ridges will continue
into the afternoon.
--------------------------------------------------------------------
Surface boundary is working its way through the area this afternoon
as is a shortwave along with it. This has focusing some
flurries/sprinkles that will not amount to much if anything as they
quickly dive southeast. The morning sounding here shows the depth of
the moisture well-confined below the DGZ, so this may favor more
light drizzle than flurries. Either way, there won't be a concern
for ice in the lowlands with this batch as temperatures are now
safely above freezing.
Over in the higher elevations, probabilities still remain high for
measurable freezing rain through this afternoon. With the loss of
moisture aloft and the DGZ layer above the saturated layer, this
should lead to more of a freezing rain/drizzle threat as
surface temperatures remain around or below freezing in these
locales, so the Winter Weather Advisory remains in place for the
ridges through 7PM.
With the lack of cold air advection, or really any semblance of an
airmass change in dew points or temperatures behind the front, highs
today will be close to seasonal values under cloudy skies in a
shallow moist-layer. Wind will go light to calm tonight under high
pressure, but the blanket of clouds will offset any radiating
with lows dipping down to normal or a bit above in the upper 20s
to low 30s. Residual surface moisture and light wind may
support some patches of fog overnight.
&&
.SHORT TERM /6 AM WEDNESDAY MORNING THROUGH THURSDAY NIGHT/...
KEY MESSAGES:
- Dry Christmas Day and Thursday.
- Temperatures near normal on Christmas and increasing on Thursday.
--------------------------------------------------------------------
Heights rise Wednesday as ridging builds overhead. Surface high
pressure centered across upstate New York will increase subsidence
and should keep Christmas Day dry for our area; some guidance tries
to push some precip into our eastern Ohio counties as a weak impulse
moves through the mid-level flow, but model soundings show a strong
subsidence layer atop a very shallow moist layer that is likely
going to suppress any rain chances. Wouldn't completely rule out
some sprinkles but not seeing support for much more than that.
Increasing thicknesses and warm advection aloft under the ridge will
push 850 mb temperatures up by 4-6 degrees compared to Tuesday, but
plenty of cloud coverage will mute highs and keep them right around
normal.
Ensembles are in good agreement that the ridge will continue to
amplify on Thursday in response to a upper low digging toward Texas.
The high will not have migrated much by Thursday and will again keep
us dry but cloudy. Better warm advection at the surface will start
to modify the airmass with 50s sneaking into our southern half
with a 30-50% chance and upper 30s/40s more likely further north.
&&
.LONG TERM /FRIDAY THROUGH TUESDAY/...
KEY MESSAGES:
- Temperatures well above-average for the weekend.
- Rain returns Saturday and lingers into the start of next week.
--------------------------------------------------------------------
The eastern CONUS ridge continues to hold and strengthen Friday as a
pseudo-blocking pattern develops with 570+ dam heights a strong
likelihood. These heights are anomalous for this time of year on the
order of +2 to 2.5 standard deviations. Deep-layer sly component to
the flow will support a continuing 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 with a good chunk of the area at 80%+ both Saturday and
Sunday. Taking a look at CIPS analogs, this pattern historically has
brought some 60s south of the Mason-Dixon Line, and NBM probabilities
are right in line with this inching up to 40-60% south of
Pittsburgh both days. Temperature-wise, all signs are pointing
toward a well-above average last weekend of 2024. However,
getting out and enjoying it might not be as pleasant.
Uncertainty ramps up in the progression of a central CONUS trough
that will ultimately shunt the ridge out of here and return
precipitation chances. Surface low pressure is favored to track
through the Great Lakes off to our northwest, but exact track,
strength, and timing of precip is still fuzzy with primary cluster
disagreement on the speed of the trough and to a lesser extent the
amplitude of the present ridge. The occurrence of precip this
weekend and it coming in the form of rain is high confidence. The
timing is low confidence. A faster solution points toward Saturday
morning while a slower one holds off until late in the day. Sunday
is likely the wetter day as we finally get the upper diffluence
and jet forcing to support higher rain chances. Rain chances
will continue into early next week until the trough exits which
is very low confidence at this point given large ensemble
spread.
&&
.AVIATION /00Z WEDNESDAY THROUGH SUNDAY/...
Mainly IFR conditions in fog and stratus will continue this
evening with a weak crossing shortwave trough, and low level
moisture in place. Patchy drizzle is expected to gradually
diminish this evening after the passage of the trough. A gradual
improvement to MVFR is then expected for most airports as
slightly drier air moves across the region. The exception will
be FKL, DUJ, MGW and LBE, where IFR conditions should persist
under mainly calm wind.
Any IFR should improve to MVFR Wednesday morning, with MVFR cigs
continuing much of the day with moisture locked under a
temperature inversion. Mixing and weak dry advection should
lift cigs to VFR by mid to late afternoon, outside of FKL and
DUJ.
Outlook...
Cig restrictions are likely to continue at FKL and DUJ Wednesday
night with low level moisture in place. VFR should return
Thursday under high pressure. Restrictions are likely again
Friday night through Sunday with a crossing warm front, and
subsequent approaching low pressure.
&&
.PBZ WATCHES/WARNINGS/ADVISORIES...
PA...Winter Weather Advisory until 7 PM EST this evening for PAZ074-
076.
OH...None.
WV...Winter Weather Advisory until 7 PM EST this evening for
WVZ511>514.
&&
$$
SYNOPSIS...22/MLB
NEAR TERM...MLB
SHORT TERM...MLB
LONG TERM...MLB
AVIATION...WM
Source:
PBZ issues Area Forecast Discussion (AFD) at Dec 24, 5:46 PM EST---------------
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