Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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FXUS62 KRAH 170737

Area Forecast Discussion
National Weather Service Raleigh NC
235 AM EST Wed Jan 17 2018

A strong upper level disturbance and associated arctic cold front
will move through our region today. This will be followed bitter
cold arctic high pressure tonight into Friday morning. A warm-up
will begin Friday and extend into the weekend.


As of 235 AM Wednesday...

...Winter Storm Warning for most of Central NC through 900 PM
...Winter Weather Advisory for the SE Coastal Plain (Wayne and Sampson
through 900 PM...

Changes to the forecast...

We will have the Winter Storm Warnings and Winter Weather Advisories
run through 900 PM this evening and raise snowfall forecast amounts
in the Warning area to between 3-6 inches.

Forecast trends continue to advertise a deepening/stronger and more cut
off mid-level circulation/trough that is forecast to track east across
NC this afternoon and evening. This in turn results in a slower system
which allows more QPF. Partial thicknesses support snow as the main P-
Type over the Piedmont into the Northern Coastal Plain, arriving
between 09z and 12z in the western Piedmont, spreading east into the
Triangle area by mid morning. To the southeast of the Triangle area,
the precipitation is expected to be delayed a few hours, especially
along the Interstate 95 corridor, arriving late morning or early
afternoon. The delayed system down east means that the precipitation is
expected to begin as rain, then transition to snow as the cold air wins
out mid to late afternoon.

Current data indicated the arctic front had reached through the
Mountains and extended NE across central VA. Bitterly cold temperatures
behind the front ranged from near zero over TN and in the 20s into
Mountains of NC and over northern VA. Temperatures were mainly in the
30s over central NC, with dew points in the 20s. The partial thicknesses
and wet bulb temperatures were already supportive of snow over most
of the Piedmont, and that is before the arctic air begins to be pulled
into the region after 12z. In addition, a low pressure was developing
along the arctic front over north Georgia. A light southerly flow into
the low pressure has aided in the increase of boundary layer moisture
(dew points in the 30s along the Savannah River in GA/SC and nosing up
into northern SC. This moisture will be transported into the system as
the mid/upper trough sharpens and cuts off through the day and the low
pressure tracks along the front. The strengthening upper feature is
responsible for the introduction of more lift/moisture transport/QPF.
This QPF is expected to be maximized over central NC late morning into
the afternoon with moderate to heavy snow.

Snowfall details...

As for the snowfall forecasts, it appears that a QPF of 0.30 to 0.50
liquid equivalent is most likely across central NC. This uses a blend
of the models. Using the 10:1 becoming 15-18:1 snow to liquid ratios
would give most of the Winter Storm Warning area between 3-5 inches in
the northwest, 3-6 inches from SW to NE through the center of the
Piedmont into the Northern Coastal Plain, and lesser 1-3 totals in the
SE Coastal Plain (which occurs at the end of the event). The least
totals should be in the Clinton to Goldsboro areas where 1-2 inches is
expected. Snowfall rates of 0.5 to nearly 1 inch an hour will be
possible for 4-6 hours given the latest guidance through the Piedmont
and Northern Coastal Plain.

Temperatures, precipitation timing, and P-Type details...

Snow is expected to develop over the Triad and Yadkin Valley region by
12z, with the heaviest snow between 12z and 18z, gradually tapering to
flurries mid to late afternoon. Temperatures will fall into the lower
to mid 20s. Snow is expected to spread into the Triangle and western
Sandhills region this morning, with the heaviest snow expected between
10 am and 4 pm. Temperatures will fall into the mid to upper 20s this
afternoon. The snow will likely begin as a period of rain in the
Central and Southern Coastal Plain late morning, then gradually
transition to snow from NW to SE as the cold air works in. Dynamical
cooling associated with heavier precipitation rates will also aid in
the change-over to snow from Fayetteville to Goldsboro mid to late
afternoon. Temperatures in the mid to upper 30s will fall quickly by
mid to late afternoon into the lower 30s in the Advisory Area. The
temperatures will drop quickly today as the arctic air surges in from
the north as the precipitation reaches maximum intensity.

Expect the snow to taper off from the west late this afternoon and
evening. Clearing skies will lead to bitterly cold conditions tonight.
Lows 8-18.


As of 230 AM Wednesday...

Continued very cold with mostly clear skies. Highs only in the upper
30s to lower 40s Thursday. Lows Thursday night in the teens to lower


As of 230 AM Wednesday...

The extended forecast will feature a warming trend as the upper level
pattern transitions to more ridging in the SE and a trough out west.

A moderation in temperatures will be slowed by melting snow Friday and
Saturday when highs will be in the 40s Friday and upper 40s and 50s
Saturday. Lows in the 20s.

By Sunday, it should be much milder with highs 55-65.

The mild conditions will persist into early next week as the flow in
the mid-upper levels remain zonal. An upper level disturbance will be
lifting well to our nw Monday. This system`s attendant cold front will
approach and cross our region Monday and Monday night, increasing the
chance of showers.


As of 1245 AM Wednesday...

24-Hour TAF Period: Snow will develop and spread into the KINT/KGSO
and KRDU areas through 15z. CIGS and VSBYS will lower into the IFR
to LIFR categories at times between 12z and 18z in the west, and
between 15z and 21Z at KRDU. The snow will gradually taper off and
end from the west between 21z and 00z/this evening.

In the KFAY and KRWI areas, precipitation is expected to start as
rain between 13z and 15z, then change to snow with MVFR CIGS/VSBYS
forecast to lower to IFR between 19z and 23z. The snow will end by
around 00z, with CIGS and VSBYS forecast to become VFR by 06z/Thurs.

Outlook 06z/Thursday through Monday... Generally VFR conditions


Winter Weather Advisory through 9 PM EST Wednesday for NCZ078-089.
Winter Storm Warning through 9 PM EST Wednesday for NCZ007-021>025-
Winter Storm Warning through 9 PM EST Wednesday for NCZ008>011-026>028-


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