200
FXUS61 KCTP 060004
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
704 PM EST Wed Feb 5 2025

.SYNOPSIS...
* Wintry, icy mix to bring hazardous travel conditions and
  perhaps power outages overnight into Thursday morning across
  central Pennsylvania
* Additional periods of potentially impactful snow and ice are
  forecast in the next 7 days: 1) this weekend (centered around
  Saturday night) and 2) early next week (centered around
  Tuesday)

&&

.NEAR TERM /UNTIL 7 AM THURSDAY MORNING/...
Still very dry out there, which continue to keep precip at bay.
It could also delay it further out in time, but only an hour or
two. We have been trying to put that message out there with the
last update or two. All the points made below are still the
thinking of onset times and precip type (more sleet than
freezing rain for the overnight).

Prev...
15-20F degree dewpoint depressions or T/Td spread continues to
prevent light snow returns over the southern tier counties from
reaching the ground. This setup should eventually help to
enhance the llvl cold air due to favorable evaporative cooling
and wet bulb effects as precip begins to spread from southwest
to northeast and pick up in intensity late tonight.

Outside of a couple of flurries or some very light snow, we do
not expect any significant winter weather prior to 10-11 PM.
The latest model trends have slowed the onset/arrival of the
wintry mix which is always tricky given WAA precip tends to be
early and not late. We decided to communicate the [most likely]
later arrival times without pushing back start times of WSW/WWY
to avoid confusion.

Progressive shortwave trough over the Great Plains this
afternoon will reach the Mid-Atlantic region late tonight. 850mb
LLJ associated with this feature is progged to remain fairly
robust at 50kt and will be a significant contributor to not only
the advection of moisture, but also of a prominent WAA regime
that will allow for a mixed wintry ptype pattern as we move
through the core of the event overnight into the predawn hours
through early Thursday afternoon.

Cold air filtering/draining east of the Allegheny front to the
south of retreating 1030mb high will be enhanced by wet bulb
effects as WAA precip expands into dry/low dewpoint airmass
situated across the central mtns and Susq Valley. Limited mixing
within the lower BL combined with evap cooling will thwart a
rapid warming of the primary thermal layer located from the
surface to 850mb. However, the layers above will warm quickly
with a sharp nose of WAA being progged within the 850-650mb
layer. This will lead to a dominant IP/ZR mixed icy ptype after
perhaps a very short window of light snow on the front/leading
edge of the main moisture plume. Travel conditions are likely to
be at their worst during the predawn/early morning commute.

&&

.SHORT TERM /7 AM THURSDAY MORNING THROUGH THURSDAY NIGHT/...
Significant icing from ZR remains focused over the Laurel
Highlands with 0.25-0.50" expected. To the east of US-219, the
latest trends for sleet accumulation has been gradually ticking
higher in the WPC WWD with up to 1" possible particularly in the
interior central mtns and upper ridge/valley locations near the
I80 corridor. A colder pocket entrenched over the east central
and northeastern zones may also foster more sleet than freezing
rain. Overall, expect a general snow/sleet quickly shifting to
sleet/zr to zr/fzdz/rain/dz transition over the course of the
event from southwest to northeast as temps rise above the
freezing mark by late morning/early aftn. Models could be too
bullish on how quickly temps rise through the morning hours, but
even so we should see a reduced/declining icing impact with
readings hovering AOA the freezing mark. Highs likely to be set
late in the day or toward the evening as the llvl cold air
scours out as flow shifts to the west.

Aside from some lingering pockets of drizzle/mist, the bulk of
precip ends by 1PM. Some upslope low clouds could persist along
the higher terrain with some peaks of sun possible downwind of
the mtns by the end of the day. It will be breezy late tomorrow
and tomorrow night with gusts 30-40 mph over the Alleghenies.

&&

.LONG TERM /FRIDAY THROUGH WEDNESDAY/...
Central PA remains between large scale weather systems on
Friday. A moisture challenged cold front is likely to cross
central PA early in the day with a reinforcing shot of colder
air accompanied by a period of flurries or light snow showers
possible over mainly north central PA. The center of high
pressure builds over western PA Friday night and is over central
PA Saturday morning, as a flat wave gathers moisture from the
central Mississippi to the Tennessee River Valley. Clouds lower
and thicken by Saturday afternoon with a snow/sleet mix
developing from south to north by mid to late afternoon,
transitioning to freezing rain over southern areas Saturday
evening, and perhaps to plain rain over portions of the Lower
Susq before ending in the predawn hours Sunday. This system will
likely be impactful for travel from Saturday evening through
Sunday morning, and likely another Advisory-criteria (vs
Warning) event based on QPF limitations. Flurries or snow
showers are expected over western and northern areas behind this
system for the rest of Sunday.

Another flat wave in the parade of systems moves south of the
PA/MD border on Monday likely brushing the south with some light
snowfall. The baroclinic zone lays in wait from the next
upstream wave in the train of systems, and another flat wave
continues to brush the southern quarter to half of central PA
with light snow Tuesday into Wednesday. A slight waggle north
would bring more significant precipitation into play for south
central PA, so we`ll continue to watch this play out, but one
system at at time.

&&

.AVIATION /00Z THURSDAY THROUGH MONDAY/...
00z update... VFR/unrestricted conditions should persist across
the Central PA terminal sites until later this evening (at
least through 04-06z).

Overnight, there is high confidence (90+%) that a wintry mix of
sleet and freezing rain will overspread PA, with an onset time
range of generally 06-08z. Once again, with a high degree of
confidence (90+%), we anticipate several prevailing aviation
hazards Thursday morning (through 14-16z), namely some
combination of sleet and freezing rain, IFR restrictions, and
low-level shear (as a S-SW jet maximum of 35-50 kt overruns SE
surface-based flow).

Thursday afternoon (after 16-18z), surface temperatures should
slowly climb above freezing, as steadier precipitation tapers
off and ends. We anticipate IFR-fuel alternate ceilings, with
surface winds veering into the W-SW.

Outlook...

Fri...MVFR cigs possible early over the western airspace;
otherwise VFR with no sig wx.

Sat...Sub-VFR restrictions associated with a wintry mix.

Sun...Sub-VFR cigs possible, especially over the western
airspace.

Mon...Snow possible, mainly over south central PA.

&&

.CTP WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory from 10 PM this evening to noon EST
Thursday for PAZ004>006-010>012-018-019-026>028-036-037-041-
042-045-046-049>053-056>059-063>066.
Ice Storm Warning until noon EST Thursday for PAZ017-024-025-
033>035.

&&

$$

SYNOPSIS...Steinbugl
NEAR TERM...Dangelo/Steinbugl
SHORT TERM...Steinbugl
LONG TERM...DeVoir/Dangelo/Banghoff
AVIATION...Jurewicz/Steinbugl