PBZ issues Area Forecast Discussion (AFD) at Jan 25, 6:58 PM EST278
FXUS61 KPBZ 252358
AFDPBZ
Area Forecast Discussion
National Weather Service Pittsburgh PA
658 PM EST Sat Jan 25 2025
.SYNOPSIS...
Clouds will continue to increase this afternoon ahead of an
approaching disturbance. Snow chances will also return,
generally north of I-70. Some areas north of Pittsburgh could
see around an inch of accumulation by Sunday morning. Dry
weather returns Sunday night and Monday under weak high
pressure.
&&
.NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...
KEY MESSAGES:
- Snow chances increase by late afternoon, especially north of
Pittsburgh.
- Snow totals of around an inch are possible near US-422, with
less elsewhere.
-----------------------------------------------------------------
Evening Update: Swath of radar returns are crossing the area
late this afternoon, but dry air at the surface has inhibited
snow from making it to the ground. Area dew point depressions
remain around 15-20 degrees, with little likelihood of
saturating the column for at least the next several hours. Have
dropped PoPs back significantly through 00z and lowered snow
accumulation through 06z to account for this. Primary
accumulation overnight will be in the higher terrain and
possibly north of I-80.
Previous...
An approaching shallow mid-level trough, along with warm
advection, is pushing increasing clouds into northern PA and
eastern Ohio at this time. Ceilings remain in the 6-7 thousand
foot range at lowest. Low-level dry air is remaining a bit more
pronounced than expected earlier, and this is currently
inhibiting any precipitation from reaching the surface, and may
continue to do so until the lower levels saturate. This has
introduced complications and reduced confidence somewhat in the
overall snow forecast.
Overall expectations remain that much of the snow late this
afternoon and tonight will remain to the north of Pittsburgh.
Latest HREF means/composite reflectivity probabilities suggest
a more focused area: a maximum of snow coverage along a band
near or just north of US-422. Here, the best intersection of
moisture and low level jet-supported ascent appears likely to
occur. Still, as noted, overall moisture availability appears
lower on the latest runs, particularly near the surface. This has
cut down overall QPF/snow expectations. HREF probabilities of
an inch or greater (10:1) are below 50 percent everywhere except
portions of Jefferson/Indiana counties. With snow ratios
expected to be closer to 15:1, a 1 to 2 inch total is possible
in this general area by tomorrow morning, with an inch or less
extending westward toward the Ohio border. Less than a half inch
is expected in the Pittsburgh metro and surrounding regions,
with little to none south of I-70 (save for a slight uptick in
the ridges). Trends will continue to be monitored, and further
adjustments are possible, particularly if lower-end model
scenarios play out.
With a crossing 40-45 knot low-level jet this afternoon, 20 to
30 MPH wind gusts (up to 40 MPH on the ridges) will continue
through sunset, with some slackening thereafter as low-level
lapse rates become less favorable.
&&
.SHORT TERM /6 AM SUNDAY MORNING THROUGH TUESDAY/...
KEY MESSAGES:
- Lingering snow showers end Sunday morning
- Dry under weak high pressure Sunday night and Monday
- Snow showers return Monday night and Tuesday with a cold
front, along with gusty wind
--------------------------------------------------------------------
Isolated to scattered snow showers may remain Sunday morning,
primarily north and east of Pittsburgh, as a surface cold front
crosses. Low-level westerly flow and a relative dearth of
moisture by this point should keep any coverage on the low side
and any impact minimal, with the flow suggesting little
contribution from lake or terrain effects.
Dry weather is expected from Sunday night through Monday as weak
surface ridging builds in underneath mid-level troughing. A clearing
sky may allow temperatures to drop several degrees below normal
Sunday night, although a lingering surface pressure gradient may
keep enough wind going overnight to stunt the temperature drop.
Fairly seasonable temperatures are forecast for Monday with neutral
to slight warm advection.
The next cold front will try to sink down from the Great Lakes
Monday night into Tuesday. However, the boundary might have issues
crossing the entire CWA, as the main shortwave crosses Ontario and
the eastern Great Lakes before swinging across northern New England.
This may keep much of the snow shower activity north of Pittsburgh,
with PoPs highest in the I-80 corridor. Still, strengthening cold
advection/steepening lapse rates will likely lead to the development
of at least isolated to scattered snow showers over the region.
850mb flow of 55-70 knots overnight may create strong wind gusts
of up to 35 MPH in the lowlands and up to 45 MPH in many ridge
areas...advisory-level gusts in the higher elevations cannot be
ruled out, assuming sufficient mixing exists.
&&
.LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/...
KEY MESSAGES:
- Periodic snow chances through Wednesday night
- Lower precipitation chances through Friday, with chances
returning by Saturday
- Near to above average temperatures through Wednesday, with
cold returning by Thursday before moderating again by the
weekend
--------------------------------------------------------------------
Ensembles maintain quasi-zonal flow over the region Wednesday,
suggesting temperatures remain near to above normal. Most model
solutions then drop a shortwave across the Great Lakes and the Upper
Ohio Valley, bringing a reinforcing shot of cold air for the
Wednesday night into Friday period. Cluster analysis shows some
uncertainty with both the speed and depth of this shortwave. A small
minority of members suggest a shallow enough wave to keep
temperatures close to climatology, but the majority support a return
to below-normal values. Thus, precipitation accompanying this
shortwave is likely to remain in the form of snow. Given the
strength of the cold advection and potential moisture increase in
the DGZ, rounds of stout snow showers are a possibility Wednesday
afternoon/evening.
Isolated scattered snow showers may continue into Thursday.
Thereafter, the ensembles generally agree in the trough moving
eastward with time, with ridging returning by Friday. Again,
however, there is considerable model spread with feature speed in
strength. The majority of model clusters support some level of
ridging in the Great Lakes/northeast CONUS by Saturday afternoon,
while one cluster maintains lower heights with more of a zonal flow
look. For now, the safest play is to expect a temperature
moderation trend back towards or above climatology by Saturday.
Precipitation chances appear fairly low Thursday night/Friday, but
may ramp up again by Saturday if the majority opinion suggesting
increasing warm advection is correct.
&&
.AVIATION /00Z SUNDAY THROUGH THURSDAY/...
A weak disturbance continues to track across the region this
evening and into tonight. The low levels have been slow to
saturate as only as of 2345Z, that dew point depressions have
now lessened to 10 to 15 degrees, and some less than that. Most
ceilings have been VFR and are now getting down to low VFR and
even some MVFR observations as the swath of snow continues to
moisten up the low levels. Expect periodic MVFR cigs with the
exception of MGW, HLG, and ZZV as these terminals will seemingly
miss the swath of moisture to the north. It is very likely, in
fact the NBM probs are getting down to 80% to 90% for a MVFR
cig, for FKL and DUJ to remain at MVFR or less through the
period.
The other note for tonight will be the potential for low-level
wind shear with an expansive jet still overhead. The
uncertainty at this point stems from whether or not the surface
decouples and wind goes lighter or mixing continues. If we
decouple, LLWS is probable for sites from PIT to the south.
It is likely for the MVFR or low VFR cigs to persist through the
TAF period. Winds will be from the southwest, eventually
shifting to the west later in the period. Expect some gusts
reaching 20 knots at times but most winds will be 10 knots or
less.
Outlook...
Snow showers and breezy west winds are expected on Sunday with
some restrictions possible due to lingering stratocumulus. VFR
conditions are expected to return by Monday.
&&
.PBZ WATCHES/WARNINGS/ADVISORIES...
PA...None.
OH...None.
WV...None.
&&
$$
SYNOPSIS...CL
NEAR TERM...Rackley/CL
SHORT TERM...CL
LONG TERM...CL
AVIATION...MLB/Shallenberger
Source:
PBZ issues Area Forecast Discussion (AFD) at Jan 25, 6:58 PM EST---------------
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