Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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FXUS62 KRAH 180214

Area Forecast Discussion
National Weather Service Raleigh NC
915 PM EST Wed Jan 17 2018

An arctic cold front will move off the coast later this evening, as
a powerful upper level low pressure area crosses the region. This
low will move off the Mid Atlantic coast early Thursday. High
pressure will build in from the southwest Thursday through Friday,
bringing a warmup that will last through the weekend.


.NEAR TERM /through tonight/...
As of 915 PM Wednesday...

...Winter storm warning continues until 1 AM in areas from
Lillington and Raleigh to the NE, with winter weather advisories
elsewhere through Thu morning due to treacherous conditions...

Still seeing heavy snow bands from Johnston county to the north and
northeast beneath a strong area of upper divergence, with more
cellular and lighter/patchier snow showers from the Triangle and
Fayetteville to the west and north, beneath the passing mid level
low where stabilities are lower. Another inch or two of snowfall is
possible in the NE sections, while smaller crystals (likely needles)
and lighter amounts (lower snow-liquid ratio) will lead to little
additional accumulation elsewhere with drying aloft. The warning
will be maintained across the NE, with larger flakes and higher
rates, until closer to its expiration time of 1 AM. Elsewhere, we`ll
transition to an advisory to account for the treacherous driving
conditions as colder and rushes in with minimal sublimation. This
will all culminate in an advisory areawide overnight as even those
roads that received minimal snowfall experience black ice. Temps are
not expected to approach the freezing mark until close to noon Thu,
despite plenty of sunshine, given the high albedo due to the
snowpack. Expect lows of 10-19. -GIH

Earlier discussion from 243 pm: F-gen band centered over the heart
of central NC will translate slowly east across the remainder of the
NC Piedmont this afternoon and then into the NC Sandhills and
Coastal Plain through the evening, exiting the coastal plain
counties by around 06z. Meanwhile, the back-edge of deeper moisture
and measurable snow can be seen on GOES 16 satellite approaching the
far western/Triad counties.

Thus far, we`ve seen a broad wet snow swath of 4 to 6 inches across
the western and northern Piedmont counties, with localized higher
amounts of 7 inches maximized in an axis extending along Randolph,
Alamance, Orange and Person Counties, where the CSI mesoscale
banding feature set-up and went on to produce 1.0 to 1.5" hourly
snow rates and snow ratios on the scale of 18-20:1(outside of this
band ratios where more like 8-12:1(climo))

As this precip band shifts east through the course of the evening,
we do not expect it to be as efficient snow producer as it was over
the Piedmont counties, due to much warmer surface temps in the mid
30s to lower 40s, with a good bit of precip falling as rain before
both wet-bulb cooling and lost of daytime heating allows for a
change-over to snow.

Through the remainder of the afternoon/evening expect additional
snowfall amounts of 2 to 4 inches from the Triangle north and
northeast, tapering off to 1 to 2 inches across the Sandhills and
southern Coastal Plain, and potentially another half inch to an inch
over the Triad.

Due to the slower timing, had to extend the Winter storm warning and
advisory across the eastern half of the forecast area through 06z.

CAA overnight, along with fresh snow cover and clearing skies will
help   temperatures fall into the teens, with wind chill values in
the single digits.

Given these frigid temperatures, any snow or slush on roads and
bridges/overpasses will freeze, making for treacherous road
conditions Thursday morning.


As of 120 PM Wednesday...

H5 west to northwest flow and surface ridging will result in mainly
clear weather.  Temperatures will start very cold with highs on
Thursday in the upper 30s to lower 40s. After lows in the teens to
lower 20s Thursday night, temperatures will moderate to near
seasonal normals on Friday.


As of 120 PM Wednesday...

The warmer weather will continue into the weekend as the upper level
pattern transitions to more ridging in the SE and a trough in the
western US.

A storm system will move northeastward from the central plains
Sunday to the western Great Lakes on Monday.  This system`s
attendant cold front will cross our region Monday night with a
chance of showers. Temperatures in the 50s Saturday afternoon will
climb to around 60 on Sunday, and 60 to 65 on Monday. After the cold
front passage, temperatures Tuesday and Wednesday will fall back
into the 50s.


As of 640 PM Wednesday...

24-Hour TAF Period: Sub-VFR conditions and snow continue as of 2330Z
this evening. The back edge of the snow should make its way through
KINT and KGSO by 03Z, through KRDU and KRWI by 06Z and KFAY by 08Z.
Conditions will improve back to VFR quickly after the snow ends,
with clearing skies by 06Z in the Triad and by 12Z at KRWI. Winds
will remain a bit strong and gusty tonight, gusts of 18-22 kts
lasting longest in the south and east. Otherwise, winds will back to
more westerly on Thursday at 5-10 kts. Depending on the intensity of
the snow, visbys will range anywhere from 2-5SM (-SN) to 1/2-2 (SN)
down to 1/4 mile (+SN).

Looking ahead: VFR conditions will persist through Saturday.
Forecast soundings hint at some low-level moisture Saturday night,
otherwise the next chance for adverse aviation conditions will occur
Monday night into Tuesday.


Winter Weather Advisory until 1 AM EST Thursday for NCZ078-089.
Winter Weather Advisory until noon EST Thursday for NCZ007-
Winter Storm Warning until 1 AM EST Thursday for NCZ008>011-


NEAR TERM...Hartfield/CBL
SHORT TERM...Franklin
LONG TERM...Franklin
AVIATION...KC is the U.S. government's official web portal to all federal, state and local government web resources and services.