438
FXUS62 KRAH 101200
AFDRAH

Area Forecast Discussion
National Weather Service Raleigh NC
700 AM EST Fri Jan 10 2025

.SYNOPSIS...
Arctic high pressure will settle into the lower Middle Atlantic
today. An area of low pressure will track northeast from the Gulf
coast today to the North Carolina coast tonight, and then offshore
on Saturday. High pressure will build back in through Sunday.

&&

.NEAR TERM /THROUGH SATURDAY/...
As of 450 AM Friday...

* Confidence remains high that an impactful winter storm will affect
  central North Carolina from this afternoon through Saturday
  morning.

An area of low pressure near the Louisiana coast early this morning
is expected to lift ENE through the Southeast and off the NC coast
by Sat morning. Very dry and cold antecedent conditions over the
Southeast and Mid-Atlantic have primed the environment for a
widespread winter storm to bring minor to moderate impacts to a
majority of central North Carolina. There still remains a
considerable amount of uncertainty with regard to the freezing rain
amounts and related impacts, so stay tuned to regular updates as the
forecast may change drastically as observational trends are assessed
over the next 12 hrs.

Snow: The event will likely begin as predominantly snow and some
sleet at the onset of precipitation moving in from the west
beginning to reach the ground in the Triad around rush hour (4-6PM).
Surface temperatures are expected to be initially above freezing,
but will rapidly drop below 32 degrees as precipitation begins to
reach the ground. Given the multiple days of very cold conditions,
the ground will be sufficiently cold, with 4 inch soil temperatures
mostly in the 30s this morning, which will allow for efficient and
immediate accumulation of snow. This will be very atypical compared
to a normal "Carolina`s winter event" where it would take a couple
hours for accumulation to begin. Any untreated surface will likely
become slick and hazardous to traverse. Along and north of the I-85
corridor is most likely to remain mostly snow and sleet with
accumulations of 2 to 4 inches are expected. Locally higher amounts
will certainly be possible, especially where it remains all snow for
the duration of the event.

Freezing rain: Forecast confidence remains lowest with the freezing
rain accumulations and location of greatest impacts. A majority of
guidance has a swath of ice accumulations developing after midnight,
as surface temperatures drop to below freezing in the insitu CAD
regime that sets up at precipitation onset, however vary on its
placement. Latest forecast leans heavily on the cooler guidance
(ECMWF and Canadian) to lock in the CAD over a majority of our area
with some surface temps rising above freezing in Cumberland,
Sampson, and Wayne. This blend results in multiple hours of freezing
rain accumulation from Wadesboro to Sanford and southern Wake County
through Smithfield and Rocky Mount. This forecast solution results
in 0.1" to around 0.2" in a 50-60 mile wide swath centered around
this line. Within this band, locally higher amounts in excess of
0.25" will be possible and would result in more numerous power
outages in the areas affected. Where this forecast may go wrong is
if the insitu wedge doesn`t hold over the southern Piedmont,
Sandhills, southern Piedmont and the central/southern Coastal Plain
and southerly flow and gradual warming above freezing at the surface
occurs, which would significantly narrow/lessen the freezing rain
accumulations as a transition to all rain occurs.

Sleet: In between the snow and freezing rain corridors will likely
be a transition to mainly sleet for an hour or two, but may remain
stationary for several hours as the warm nose ceases to spread
farther north. This is most likely to occur perhaps along and just
south of the I-85 corridor into the Triangle and cut into snowfall
totals to closer to the 0.5" to around 2".

By Saturday morning, precipitation will likely rapidly come to an end
in the Triad by 4-6 AM, the Triangle by 5-7 AM, and exiting the
Coastal Plain by 8 AM. Surface temperatures are expected to rise
above freezing everywhere by 11 AM. West to northwest surface winds
are expected to increase to 20 to 30 mph by late Sat morning, and
depending on snow/ice accumulations that occur overnight, may
increase the risk for continued power outages and may inhibit
restoration efforts. Infrequent gusts to around 35 mph will be
possible from the Triad eastward into the northern Coastal Plain.

&&

.SHORT TERM /SATURDAY NIGHT THROUGH SUNDAY NIGHT/...
As of 335 AM Friday...

The eastward exiting upper trough and associated surface low will be
replaced by high pressure building from the southern plains through
the beginning of next week. The airmasses associated with these highs
are typically somewhat modified, but with such a cold airmass
already in place, temperatures will continue to be well below
normal. Thicknesses and the presence of some snow suggest lows
Saturday night slightly below guidance consensus in upper teens and
lower 20s, followed by low to mid 20s Monday morning.  Black ice
will likely be an issue for a couple of nights and snow melts during
the day when highs should climb to around 40s Sunday and the mid 40s
by Monday.

&&

.LONG TERM /MONDAY THROUGH THURSDAY...
As of 335 AM Friday...

The brief pseudo-respite from frigid air Sunday and Monday will be
followed by a massive upper trough over the eastern uS and another
arctic surge of air behind a mostly dry shortwave swinging southeast
out of Canada Tuesday/Wednesday.  This will result in temps 15-20
degrees below normal midweek. Low-level thicknesses are forecast by
the ECMWF to bottom out in the near 1350m Wednesday morning, which
suggests colder conditions than the past couple of days, and the EPS
statistical guidance mean is in the mid to upper teens for lows
Wednesday and Thursday mornings. GEFS values are a little warmer but
still much below normal, and guidance also suggests some wind chills
concerns will values in the teens or approaching single digits
Wednesday and or Thursday nights.  There is still some questions as
to when the coldest night will be given uncertainty in the timing of
the trough.

The forecast will remain dry under the deep and cold trough, with no
influence from the Gulf of Mexico and an reliance on northwest flow
short waves.  Given the strength of the shortwave on Wednesday, it
would not be surprising to see flurries or isolated snow showers in
the Piedmont, but there is no real support from model guidance at
this time.

We should then see a more substantial moderating trend heading into
next weekend as the pattern is forecast to shift to troughing int he
west and southwesterly flow across the southeast US.

&&

.AVIATION /12Z FRIDAY THROUGH TUESDAY/...
As of 700 AM Friday...

Arctic high pressure overhead will favor initially dry, VFR
conditions and light and variable surface in cntl NC this morning,
during which time high through mid-level ceilings will overspread
the forecast area and become accompanied by virga. Strengthening
lift will cause ceilings to further lower into MVFR-IFR range and be
accompanied by mainly snow initially this afternoon-evening. While a
transition to mixed wintry precipitation, including sleet and
freezing rain, will spread north from FAY to near RWI and RDU
tonight, the p-type at INT/GSO will remain all or predominately
snow, including some moderate to heavy in intensity between 00-06Z.
While the p-type at FAY may briefly changeover to a cold rain or
drizzle before ending Sat morning, mixed wintry p-types will likely
continue until the precipitation tapers off Sat morning at all other
sites. Low-level wind shear will also become likely at FAY during
the last 6-8 hours of the 12Z TAF period.

Outlook: Drier air and a strengthening and gusty nwly wind will
eradicate the cold air damming regime and associated low overcast
mid-morning through midday Sat, with associated VFR conditions that
should then continue through early-mid next week.

&&

.RAH WATCHES/WARNINGS/ADVISORIES...
Winter Storm Warning from 1 PM Friday to 10 AM EST Saturday for
NCZ007>011-021>028-038>043-073>077-083>086.
Winter Weather Advisory from 1 PM Friday to 10 AM EST Saturday for
NCZ078-088-089.

&&

$$
SYNOPSIS...BLS
NEAR TERM...Swiggett
SHORT TERM...BLS
LONG TERM...BLS
AVIATION...MWS