Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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FXUS62 KRAH 211738

Area Forecast Discussion
National Weather Service Raleigh NC
140 PM EDT Sat Oct 21 2017

High pressure will extend across the Carolinas through Sunday. A
strong cold front will approach from the west Monday, and cross
central NC on Tuesday.


As of 1005 AM Saturday...

High pressure at the surface and aloft will remain in control of the
weather through tonight across central NC. Aside from some passing
cirrus, expect sunny skies and mild afternoon temperatures. Temps
will average 8-10 degrees above normal for late October, ranging
between the upper 70s-lower 80s.

The sfc ridge associated with the high will drift offshore tonight
through early Sunday. The resultant sely low level flow will advect
enough warm moist air to produce patchy fog over sections of the
coastal, plain, Sandhills, and potentially the eastern Piedmont by
daybreak Sunday. Not expecting dense fog, so no travel issues
anticipated. It will be a bit milder with low temps in the upper 40s
to around 50 nw to the low-mid 50s southeast.


As of 355 AM Saturday...

The mid-upper ridge in the vicinity of the coast of the Carolinas,
and the associated surface ridge axis extending swwd into the sern
US, will move little through the weekend. Persistence will still
largely rule, although another day`s worth of ely low level flow
around the ridge will have allowed surface dewpoints to climb more
solidly into the 50s, to around 60 degrees or so in the Sandhills
and srn Coastal Plain, by Sun evening. This will favor both slightly
higher RH values than recent days, and also (mostly) few-scattered
stratocumulus midday onward. Bufr forecast soundings from both the
NAM and GFS suggest this stratocumulus may become broken in
coverage/mostly cloudy by late afternoon-evening over srn portions
of the RAH forecast area. Cloud cover, including some low clouds and
fog centered again over ern portions of the forecast area, will
further increase into the mostly cloudy range overnight, but the
continued presence of a capping inversion aloft and lack of deep
moisture, suggest conditions will remain dry.


As of 355 AM Saturday...

Monday through Tuesday: Increasing southerly to south-southwesterly
flow in advance of a deepening mid/upper level trough and potential
closed mid level low over the lower MS valley region and deep south
along with an approaching associated cold front will lead to a warm
but cloudy weather on Monday. Chances for showers will increase
across the western portion of the area by the afternoon. However,
the main band of convection is expected to move across the area
Monday night into Tuesday morning. Low level winds profiles will
strengthen as the band of convection moves into and across the area,
while the lead mid level impulse may attempt to take on a negative
tilt. However, overall surface instability remains in question given
the non-preferred diurnal timing (high shear, but low CAPE). With
that said, instability is expected to remain rather weak and may be
the limiting factor. Given the strong low and deep layer shear any
surface based instability at all could prove very problematic, with
the potential for damaging wind gusts and even a tornado or two.
Stay tuned to this part of the forecast as a severe weather threat
may be possible Monday night into Tuesday morning. Expect high temps
on Monday will be warm in the 70s to around 80 SE, with lows on
Tuesday morning generally in the 60s.

The lead cold front and mid level dry punch is expected push the
main band of convection to the east of the area by Tuesday afternoon
(given the GFS and ECMWF current timing). This should end any severe
threat, though temps will remain rather mild with any good CAA
expected after sunset. Highs temps are expect to generally range
from the upper 60s NW (which may come in the late morning or early
afternoon) to the mid 70s SE/E.

Tuesday night through Friday: Drier and cool weather is expected mid
to late week as the deep/cold mid/upper level trough shifts across
the area. This will result in quite weather during this period, with
temps generally in the upper 50s to 60s for Wednesday and Thursday,
with temps rebounding some into the 60s and 70s for Friday as
surface high pressure shifts offshore. Low temps Wednesday morning
are expected to be in the 40s NW to the 50s SE. Lows on Thursday and
Friday morning are expected to generally range fro the upper 30s
into the 40s, with some of the usual rural cold spots dropping into
the mid 30s on Thursday morning if the MSLP gradient is able to
relax enough.


As of 140 PM Saturday...

There is a high probability that VFR conditions will persist across
central NC through 00Z Monday as high pressure at the surface and
aloft controls the weather across central NC. The exception will be
after 04Z tonight as patchy fog will develop, likely reducing the
visibility into the MVFR range, particularly in vicinity of KRWI and
KFAY, and possibly at KRDU. Pockets of IFR/LIFR visibility may occur
close to daybreak in proximity of KRWI. Pockets of fog will disperse
within an hour or sunrise.

The good aviation conditions are expected to persists through early
Sunday evening. Later Sunday night and on through Tuesday, an
approaching frontal system will draw a moist low level air mass into
central NC leading to an increased threat for sub VFR ceilings as
well as increasing coverage of showers and a few thunderstorms,
especially late Monday through early Tuesday. A return to VFR
parameters anticipated for Tuesday night through Thursday.





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