PBZ issues Area Forecast Discussion (AFD) at Jan 15, 2:23 PM EST581
FXUS61 KPBZ 151923
AFDPBZ
Area Forecast Discussion
National Weather Service Pittsburgh PA
223 PM EST Wed Jan 15 2025
.SYNOPSIS...
More widespread snowfall is expected Thursday and Thursday
night with heavy snow possible in the Allegheny Mountains.
Another system will cross this weekend before a signifigant
arctic outbreak and very cold temperatures next week.
&&
.NEAR TERM /THROUGH TONIGHT/...
KEY MESSAGES:
- Light (minimal) snow accumulations possible north of I-80 and
in the Allegheny Mountains today.
- Dry, but chilly, elsewhere.
--------------------------------------------------------------------
Shallow moisture remains trapped under the subsidence inversion
today downstream of the Huron/Erie fetches. This will maintain
light (i.e. minimal) snow shower chances primarily north of I-80
and in the higher terrain today. Flurries and isolated dustings
are possible elsewhere. So far this has not amounted to much and
will radually taper this evening as flow backs westerly in a
brief bout of ridging.
High temperature remains 10 to 15 degrees below normal, with
most of the area topping out in the lower 20s (mid/upper teens
in the higher terrain). Brief ridging overnight should help cut
off any lingering lake showers.
&&
.SHORT TERM /THURSDAY THROUGH FRIDAY/...
KEY MESSAGES:
- Heavy snow possible in the higher terrain Thursday and
Thursday night. 1 to 3 inches possible elsewhere.
- Still below-normal, but gradually warming temperatures.
--------------------------------------------------------------------
The next mid-level wave will cross the Great Lakes Wednesday
night into Thursday. Synoptic lift through the dendritic zone
maximizes during the daytime hours, leading to widespread light
and fluffy snow in the lower elevations. Ground conditions
remain cold with a snowpack in many places, so even light
snowfall could make for hazardous travel conditions during the
day as we saw with Tuesday's snowfall. This has justified the
issuance of a winter weather advisory for the lowlands despite
totals largely being below advisory criteria.
Winds will veer more westerly by Thursday afternoon as the
trough axis crosses, leading to enhanced upsloping and heavy
snow in the higher elevations Thursday afternoon into the
overnight. Snow should persist through Thursday night in
northwest flow, however the Great Lakes are beginning to show
some surface ice accretion that may limit moisture transfer
(mostly for Erie). Modeled lake ice has most of the lake having
~80% ice coverage my Thursday night. Nonetheless, there is a
>90% chance for warning criteria in the highest ridges which has
required an upgrade from a watch to a winter storm warning.
Confidence in totals across the ridges remains somewhat
uncertain. CAMs have come into range and largely agree with a
4-8+ inch accumulation range across the higher elevations. This
is similar to deterministic global runs. However, ensemble
members have mostly been clustered around lower total solutions,
though with an upward trend. Blended guidance in particular has
been slow to catch up with hi-res guidance, making NBM and WPC
Super Ensemble probability guidance of questionable utility with
this cycle. These totals have been increased with confidence in
totals exceeding an inch or two increasing.
&&
.LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/...
KEY MESSAGES:
- A mixed precipitation event is forecast this weekend.
- Arctic outbreak with dangerously cold temperatures and wind
chills is increasingly likely early next week.
--------------------------------------------------------------------
Into Friday, rather abrupt ridging sets in, allowing for nearly
isothermal layers in the 900mb to 700mb layer. While surface
cold air will be stubborn to evacuate completely, highs will
approach average Friday and potentially rise above average
Saturday. The next day of above average temperatures would only
be the 2nd of the month.
By Saturday, the next trough approach will be enough to
encourage cyclogenesis and advect in moisture from the Gulf,
allowing precipitation chances to return with high confidence.
Precipitation type is lower confidence. For now, the most likely
scenario (as shown by the majority of guidance) has rain for
Pittsburgh and point south and east, snow along the I-80
corridor, and mixing elsewhere. In a lower probability scenario,
the warm advection is stronger and the cold air is more
stubborn to leave, which could result in a brief bout of
freezing rain Saturday. This will need to be monitored.
.. Important ..
Confidence in an arctic outbreak early next week continues to
grow. The CPC has hoisted a high risk of much below average
temperatures, with the coldest days shaping up to be next Monday
through Wednesday.
Temperatures as low as 25 degrees below average with nighttime
lows dipping into the negatives. Most guidance leans colder, but
there remain a couple of scenarios that could lead to
warmer temperatures. In the first scenario, the western trough
is is stronger, provokes eastern flow to orient more quasi-
zonal with an eastern jet positions more WSW to ENE. The warmest
possible solution in this scenario is Monday/Tuesday highs in
the 20s with lows in teens. In the second and increasingly
likely scenario, the western trough is weaker, allowing eastern
troughing and advection of Arctic air across the area. This
would tend toward daytime highs in the single digits
Monday/Tuesday with lows in at least the negative single digits
Monday/Tuesday/Wednesday morning. Widespread wind chills ranging
from -10 to -20F are currently forecast for Tuesday/Wednesday
mornings, with values as low as -30F possible in the higher
elevations. Stay tuned to the forecast for updates.
&&
.AVIATION /19Z WEDNESDAY THROUGH MONDAY/...
This morning, the lake effect band extending from Lake Erie
southeastward to eastern Westmoreland/Fayette counties is
expected to shift northward around 17z/18z as the 850mb winds
shift from northwest to west. Areas within the snow showers will
see IFR conditions.
MVFR conditions expected to persist through the remainder of the day
and briefly become VFR for most ports aside from DUJ/FKL. By
Thursday, MVFR conditions will return along with snow showers. By
Thursday night, there os a 40%-50% chance for IFR conditions at PIT,
AGC, BVI, HLG, and FKL.
General west and southwesterly winds expected to persist through the
TAF period. Expect some wind gusts around 20 knots during the day
today and tomorrow with gusts easing overnight.
Outlook...
Improvement is expected Friday under a ridge of high
pressure, but another system Saturday likely brings another round of
lower ceilings and visibilities.
&&
.PBZ WATCHES/WARNINGS/ADVISORIES...
PA...Winter Weather Advisory from 4 AM Thursday to 4 AM EST Friday
for PAZ007>009-013>016-020>022-029-031-073-075-077-078.
Winter Storm Warning from 7 AM Thursday to 7 AM EST Friday for
PAZ074-076.
OH...Winter Weather Advisory from 4 AM Thursday to 4 AM EST Friday
for OHZ039>041-049-050-058-059-068-069.
WV...Winter Weather Advisory from 4 AM Thursday to 4 AM EST Friday
for WVZ001>004-012-021-509-510.
Winter Storm Warning from 7 AM Thursday to 7 AM EST Friday for
WVZ511>514.
&&
$$
SYNOPSIS...Rackley/Milcarek
NEAR TERM...Rackley/Milcarek
SHORT TERM...Rackley/Milcarek
LONG TERM...Rackley/Milcarek
AVIATION...Lupo
Source:
PBZ issues Area Forecast Discussion (AFD) at Jan 15, 2:23 PM EST---------------
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