PBZ issues Area Forecast Discussion (AFD) at Jan 23, 12:51 PM EST678
FXUS61 KPBZ 231751
AFDPBZ
Area Forecast Discussion
National Weather Service Pittsburgh PA
1251 PM EST Thu Jan 23 2025
.SYNOPSIS...
Below normal temperatures will continue the remainder of the week
with a chance of light snow showers later this afternoon and
into the evening. Temperatures will moderate some for the
weekend but still remain below normal.
&&
.NEAR TERM /THROUGH TONIGHT/...
KEY MESSAGES:
- Temperatures will begin to moderate today.
- Light snow possible during the evening with minimal
accumulation.
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Cloud coverage is again on the increase from west to east today
in tandem with a passing mid-level wave which is working through
Ohio late this morning. Upstream observations have shown some
very light snow reaching the ground, though large dew point
depressions are making it tough. Moisture in the low levels
will be scarce with the passage, and the best chances for snow
showers locally will likely come later this afternoon and
evening along and ahead of a weak boundary as opposed to the
impulse.
Latest guidance still offsets the passage of the wave
and the boundary, so the overlap of forcing will be displaced.
Better moisture return will come just ahead of the boundary with
a more saturated DGZ and at this point HREF hourly probabilities
for measurable snowfall reach 30-60%, highest in the higher
elevations. The more persistent snow will be across the ridges
with orographic ascent, but the moisture issue will still
remain. Bumping up to the HREF 90th percentile accumulated QPF,
totals outside of the ridges don't eclipse about 0.05", so
assuming an 18-20:1 SLR, highest totals within the snow showers
should be less than an inch with potentially up to 1" or so in
the ridges. Timing looks to be after the evening rush, so peak
travel shouldn't see a notable impact, but with road
temperatures at or below freezing, it will easily accumulate on
surfaces.
&&
.SHORT TERM /FRIDAY THROUGH FRIDAY NIGHT/...
KEY MESSAGES:
- Mostly dry Friday with slightly colder temperatures.
--------------------------------------------------------------------
Snow chances taper off on Friday as surface ridging re-
establishes from the southwest and we're sandwiched between two
mid-level waves. Highs will take a hit back down a few degrees
as some colder air works in in west-northwest flow. A shallow,
near dry-adiabatic layer with cold advection at the 850 mb level
will steepen lapse rates and tap into elevated flow aloft.
Momentum transfer isn't all that impressive with only 15-20 knot
flow, so wind may take on more of a 5-10 mph sustained nature
with sporadic gusts.
&&
.LONG TERM /SATURDAY THROUGH WEDNESDAY/...
KEY MESSAGES:
- Below average temps are expected to linger through early next
week.
- Rounds of weak disturbances will produce scattered snow
chances.
--------------------------------------------------------------------
A lead shortwave will slide through zonal flow locally on Saturday
with relatively good agreement among the ensembles. Surface high
pressure progged across the Carolinas is favored to keep us dry,
though can't entirely rule out very low-end snow shower chances
confined north of I-80 in the evening as a warm front lifts through.
The better chance, albeit with low accumulation potential, will come
on Sunday. Ensembles bring a second wave with minor disagreement on
its depth, as surface low pressure drags a cold front through. One
ensemble cluster with a deeper shortwave suggests slightly higher
probability of >0.5" extending down off of the lake, but even in
this scenario, the chance of reaching 1" is less than 20%. The
primary issue looks to be available moisture as the lack of
amplification with westerly mid-level flow isn't pulling from a
great moisture source region.
Weekend temperatures will moderate in comparison to the past
week, but continue to remain below average with afternoon highs
in the upper 20s/low 30s and overnight lows in the low 20s
through Sunday. Probabilities to eclipse the freezing mark for
highs are better on Sunday extending a 50-70% chance as far
north as Pittsburgh.
Ensembles eject yet another shortwave on Monday through the still
established westerly zonal flow. Noted disagreement comes into play
at this point with the progression of the upper levels as some
clusters exhibit a potentially phased solution with a southern
stream and northern stream shortwave. Others keep them unphased and
weaker with quick progression through the area. Most of the guidance
is not bullish on much with this disturbance either as we again lack
sufficient deep layer moisture. The mean QPF from 3/4 clusters
through Monday night is generally <0.10" areawide, with the 90th
percentile as high as 0.15", which would suggest low-end snow
accumulation potential. The outlier at this point is one cluster
that suggests a much deeper, phased, and slower trough. This
solution points toward more QPF and more representative of the
current NBM 90th percentile suggesting 1-2 inches or so in the
ridges. Overall confidence is low, but the trend points toward
a lesser impact event.
&&
.AVIATION /18Z THURSDAY THROUGH TUESDAY/...
Expect VFR ceilings to begin the period but a stratocu layer
ahead of the an approaching cold front will impact the area
this afternoon/evening. A swath of snow showers is expected to
develop and move through the area between 22z and 05Z. Some
visibility may be reduced below MVFR but the main impact will be
MVFR visibility. With the approaching stratocumulus layer,
expect MVFR cigs as well. In fact, the NBM probs give 50% to 80%
for MVFR cigs. Winds will be from the southwest through much of
the period with some gusts to 20 knots at times. These winds
will shift to from the west tonight with the MVFR cigs
continuing through the night at most terminals.
Outlook...
MVFR cigs are likely to continue through Friday under cold NW
flow and a crossing upper trough. VFR returns late Friday
through early Saturday under high pressure. Restrictions and
snow showers are then possible through Sunday with a crossing
cold front. VFR returns Monday under high pressure.
&&
.PBZ WATCHES/WARNINGS/ADVISORIES...
PA...None.
OH...None.
WV...None.
&&
$$
SYNOPSIS...88
NEAR TERM...MLB
SHORT TERM...MLB/88
LONG TERM...MLB/88
AVIATION...Shallenberger
Source:
PBZ issues Area Forecast Discussion (AFD) at Jan 23, 12:51 PM EST---------------
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