933
FXUS62 KRAH 081817
AFDRAH

Area Forecast Discussion
National Weather Service Raleigh NC
120 PM EST Wed Jan 8 2025

.SYNOPSIS...
Arctic high pressure will migrate from the Great Plains to the
Middle Atlantic through Thursday. Low pressure will develop over the
northwestern Gulf of Mexico Thursday night, then track northeastward
across and offshore the South Atlantic states Friday through early
Saturday.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 1125 AM Wednesday...

Sunny, but very cold this afternoon and tonight.

The center of the strong arctic high pressure was over the central
Plains this morning (1040+ mb). Surface temperatures at late morning
ranged in the in the upper 20s to lower 30s. Winds were from the NW
at around 10 mph, producing wind chill values as low as 19 at
Roxboro at 1100 AM. The wind will slowly diminish this afternoon.
However, it will remain cold with plenty of sunshine.

Another cold front will move through the region this evening. Winds
will increase again to 10-15 mph tonight. Some gusts to 20-25 mph
can be expected this evening. Lows will be in the 15-20 range NW to
lower 20s SE.

Those late tonight-early Thu morning will be very near Cold Weather
Advisory criteria of 5F and 10F in NW Piedmont. Regardless of
whether that headline is ultimately needed/later issued, the cold
will be dangerously so for those without access to shelter.

&&

.SHORT TERM /THURSDAY AND THURSDAY NIGHT/...
As of 415 AM Wednesday...

In the mid/upper-levels, a ridge will progress from the MS Valley to
the Appalachians, downstream of a phased, longwave trough that will
extend from near Hudson Bay swwd to the Gulf of CA by the end of the
period. While strongly rising heights aloft will result across cntl
NC, a 150 kt swly upr jet downstream of the aforementioned phased
trough aloft will cause a plume of cirrostratus to stream across
particularly the wrn Carolinas very late Thu night-Fri morning. The
arrival of those clouds, after a sunny and cold day Thu with
temperatures in the mid 30s to around 40F, may cause temperatures
Thu night to steady or a rise a degree or three toward sunrise over
the srn/nwrn Piedmont. Very cold overnight lows are otherwise
forecast to again reach the mid teens to around 20F, coldest over the
ne Piedmont and nrn Coastal Plain where clear will prevail longest,
as the center of the Arctic surface high settles overhead.

&&

.LONG TERM /FRIDAY THROUGH TUESDAY/...
As of 420 AM Wednesday...

* Timing, precipitation types, and amounts for the upcoming winter
  system will be susceptible to large changes over the next 24
  to 48 hours as model guidance hones in on the most likely outcome.

The main sensible weather concern during this period will be the
already well advertised winter system Fri into Sat. Now that we are
3 to 4 days out from this event, we can start to take a closer look
at deterministic medium range models and investigate the finer
details, which bring to light some important concerns to the mainly
rain/snow event that has be advertised in the previous forecast
discussions.

Although the track of the low is a classic Miller A cyclogenesis
pattern, the area of low pressure is generally weak and lacks a
closed low at 850mb as it progresses across across the Carolinas.
This open wave at 850mb is able to more effectively advect warm air
aloft into the Carolinas, even on the north and northwest side of
the surface low. This would introduce more mixed p-type
precipitation, including freezing rain, into an otherwise mainly a
rain/snow event indicative of a pattern of a more well-established
and deepening Miller A surface low. This will place an even greater
importance on the track and timing of the surface low as it
approaches the region.

Investigating further from a cluster analysis perspective highlights
the most likely scenario as one with a more progressive northern
stream trough to our north and a quicker evolving system (impacts
Fri evening through Sat morning). The quicker northern wave would
help prevent the 850mb 0C isotherm from rippling too far north into
our area and favoring mostly snow/sleet across our area outside of
the Sandhills and southern Coastal Plain which may transition to
rain/freezing rain. Latest forecast leaned more heavily on this
solution and results in a longer period of all snow with a
transition to wintry mix Sat morning as dry air aloft shuts off ice
crystal growth.

A very important caveat is that the other most plausible scenario
results in a very different outcome for central NC. This pattern
features a slower evolving mid/upper pattern (impacts late Fri night
into Sat afternoon) and results in the warm nose aloft lifting
deeper into central NC, shifting the mostly snow regime to along and
north of the I-85 corridor, and introducing a greater freezing rain
threat south of the I-85 corridor. The forecast will likely continue
to change as we start move into the range of higher-resolution NWP
guidance so be sure to check back to the local forecast regularly
over the coming days for the latest updates on trends to which
scenario is likely to evolve.

&&

.AVIATION /18Z WEDNESDAY THROUGH SUNDAY/...
As of 120 PM Wednesday...

Arctic high pressure building ewd from the cntl Plains will maintain
VFR conditions over cntl NC through the 12Z TAF period and beyond
until Friday afternoon-evening. NW winds may become a bit gusty to
20-25kt for a period this evening when the cold front comes through.

Outlook: A low pressure system will affect cntl NC with wintry mixed
precipitation and flight restrictions late Fri through early Sat.

&&

.RAH WATCHES/WARNINGS/ADVISORIES...
None.

&&

$$
SYNOPSIS...MWS
NEAR TERM...Badgett/MWS
SHORT TERM...MWS
LONG TERM...Swiggett
AVIATION...Badgett/MWS