Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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FXUS62 KRAH 240233

Area Forecast Discussion
National Weather Service Raleigh NC
1020 PM EDT Sun Sep 23 2018

A backdoor cold front will stall over SC early Monday. Behind the
front, cool high pressure will extend southward through central
North Carolina through Tuesday. Weak low pressure will track
northward over coastal North Carolina Tuesday night into Wednesday.


As of 1020 PM Sunday...

The backdoor cold front has settled into the southern part of NC as
of late evening. It has brought a wind shift to the NE along with
much cooler air into most of the northern two thirds of central NC.
Roxboro and Henderson were already in the lower 60s, with the Triad
and Triangle areas in the mid 60s. This is noteworthy given that RDU
has only fallen into the upper 60s 8 of the 22 nights thus far in
September, and the fact that the average low is currently 59.

There has been some very light mist and drizzle over the northern
Piedmont, but essentially only trace amounts. The stable conditions
at the surface were combining with a robust temperature inversion
near H9 to cap off convection over central and eastern NC. This is
not true along the east slopes of the Blue Ridge Mountains where the
backdoor front was hung up aiding in delivering strong upward motion
above the ridges. Flash Flooding was ongoing with nearly stationary
thunderstorms west of Morganton and Marion. This activity will feed
on the more unstable air (western NC) with the front trapped along
the Mountains (keeping the convection nearly stationary).

For central NC overnight, low stratus will continue to spread south
with the CAA into the southern counties including Fayetteville and
Laurinburg. The cool and moist NE flow will allow temperatures to
fall into the 60s there as well.

The shallow cool and stable air will be trapped under the warm
inversion aloft for a good part of Monday. This will keep many areas
cloudy and cool for the morning into the early afternoon.


As of 340 PM Sunday...

The offshore-centered mid level anticyclone will build briefly W
over the eastern Carolinas Mon, while the surface ridge centered and
drifting E over the Canadian Maritimes noses SSW through central NC.
Strengthening onshore low level flow from the SE will result in
increasing moist upglide atop the weakening stable wedge, and recent
model runs generally indicate patchy light rain breaking out over E
NC (where upglide is initially strongest) before spreading inland
into central NC through the day. Will start the day mostly cloudy to
cloudy areawide, with chance pops east early, spreading NW through
the area through the day, before decreasing and diminishing Mon
night. Cloudiness will hold firm Mon night given the weak flow and
moist and somewhat stable low levels overnight. Expect highs from
around 70 NW to the low 80s SE, followed by lows in the mid to upper
60s. -GIH


As of 345 PM Sunday...

Tuesday morning the CAD will begin to loose its grip over the
Triad as a wave pulls northeast around a subtropical ridge
anchored off the east coast. As this occurs, the wedge will
start to fall apart and loose cohesion. High temperatures
Tuesday will quickly rebound with 850 mb temperatures
approaching 18 degrees C towards the Coastal Plain.
Simultaneously,an axis of PV will be located over the
Mountains of western North Carolina. This again will make for a
bimodal distribution in QPF Tuesday afternoon into Wednesday
morning. The chance of precipitation looks to move towards a
minimum Wednesday morning as the wave and aforementioned PV
exits the area. This should provide a brief period of

Wednesday evening, a long wave trough axis will center over the
central United States with an upper level disturbance pulling
northeast. The wave will quickly pull northeast though towards
Lake Ontario. The main batch of PV will miss NC, but PWATs will
climb towards 2.00" along with an approaching upper level jet
streak. This will help to increase the chance of precipitation
Wednesday evening and keep it going through Friday. The initial
shortwave mentioned above will cause a cold front to stall and
washout across the area late Wednesday. The ECMWF actually holds
onto the front as a wedge signal late Thursday, while the GFS
(and CMC) are much weaker with the front.

A secondary shortwave traversing northern Ontario late Thursday
into early Friday will be stronger than the initial wave, but
further north. This second wave will be followed by another
surface cold front. The GFS is slightly quicker and stronger
with the front compared to the ECMWF. Cooler and drier air will
exist with this front, but is nothing compared to what is was
advertised as in previous model runs. The secondary shortwave
now looks to eject far to northeast with the rex block off the
west coast of the U.S finally dislodging allowing for low
pressure to deepen. These dropping heights off the west coast of
the United States will only aide in the demise of the long wave
trough. This means that even behind the cold front temperatures
will still be near to above normal.


As of 727 PM Sunday...

24 hour TAF period: CAD wedge remains in place across the NW
resulting in sub-VFR conditions at KINT and KGSO (IFR), extending as
far east as KRDU and KRWI (MVFR). With sunset, expect a return to
IFR conditions, which are expected to linger into the late morning,
lifting back to MVFR/VFR during the aft/eve. Further east and south
(KFAY) VFR conditions remain, though expect MVFR/IFR cigs to move in
overnight and linger into the morning. Generally NE winds across the
area will remain around 3-6 kts overnight, increasing to 5-10 kts
Monday. -KC

Looking ahead: A return to IFR is expected Mon night areawide,
followed by another slow improvement to VFR Tue, with a chance of
showers and storms, greatest at RWI/FAY. Clouds and the shower/storm
coverage will increase for Wed/Thu/Fri as a front approaches from
the NW and stalls over the region. -GIH




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