Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC-- Highlight Changed Discussion --
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FXUS62 KRAH 302059
Area Forecast Discussion
National Weather Service Raleigh NC
359 PM EST Wed Nov 30 2016
A cold front will approach the area this afternoon and then move
across central NC this evening. High pressure will build into the
region on Thursday and persist through Saturday.
.NEAR TERM /UNTIL 6 AM THURSDAY MORNING/...
-- Changed Discussion --As of 355 AM Wednesday...
The upper air analysis shows a large long wave trough over the
central U.S. with a potent short wave ejecting into the western
Ohio Valley associated with a 110kt jet over western KY and TN at
500 hPa. Ahead of the trough, a deep and vigorous southwesterly
flow is present across the Southeast transporting Gulf and even
some Pacific moisture into the region with precipitable water
values ranging from 1.2 to 1.6 inches. The latest surface
analysis shows an eastward advancing cold front now crossing the
higher elevations of the southern Appalachians.
A band of showers and with embedded thunderstorms stretches from
WV into southwestern VA, western NC and SC, eastern TN into GA
with an ongoing QLCS stretching from far western SC into GA and
Given the limited forcing for ascent across central NC, the
20Z regional radar shows limited precipitation across much central
NC with an area of scattered convection (no lightning) across the
central Coastal Plain. The more significant band of showers is
moving across the mountains and into the Foothills. The vigorous
flow aloft has resulted in wind gusts up to 20 to 25kts with
sustained winds of 10 to 15 kts.
The band of convection to our west will push east reaching the
western Piedmont and Triad area between 22 and 03Z then spread
east reaching the eastern Piedmont, Triangle, and Coastal Plain
between 03Z and 09Z. SPC has our region outlooked in a marginal
risk for severe weather with the slight risk now extended into
near the SC/NC border and a tornado watch to our southwest across
western SC. The severe weather threat is largely driven by the
vigorous wind field in the high shear/low CAPE environment. The
primary limiting factor for severe convection remains the limited
instability. Peak MLCAPE values generally range around 500 J/Kg
although a pocket of higher instability, ranging from 500-1000
J/Kg may develop and persist into the late afternoon across the
central and northern Coastal Plain in an area of higher dew
points. In addition, the modest synoptic scale forcing with weak
height falls and FGEN will not compensate for the limited
instability. Finally, these parameters will become less favorable
during the evening as the convective band approaches and the
modest upper air features weaken with time and some
nocturnal stabilization occurs. Analyzed SHERBE from the SPC now
range and exceed 1 in parts of the central Carolinas and increase
to the southwest which is somewhat higher than forecast suggesting
a slightly higher damaging wind threat. Recent convection
allowing models are now maintaining the convective intensity into
the evening a little longer than from earlier this morning. So
while the message is still mixed, we are not ready declare this a
non event. As with many high shear low CAPE events, radar
vigilance and monitoring rapid changes in the mesoscale will be
The band of convection will slowly progress east this evening,
slower than progged this morning. All of the precipitation should
clear central NC by daybreak. Slow clearing will arrive behind the
front overnight. NAM and GFS BUFR soundings show a strengthening
low level jet during the evening which could result in a local
wind gust of 35+ MPH, even outside of convection. Temperatures
will fall behind the front with lows by daybreak ranging from the
upper 40s in the Triad to around 60 in the Coastal Plain where the
front will just have cleared the area. -Blaes
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.SHORT TERM /6 AM THURSDAY MORNING THROUGH SATURDAY/...
As of 230 PM Wednesday...
The synoptic cold front will have moved to the coast by 12Z tomorrow
morning, with perhaps some early morning clouds giving way to sunny
skies and cold air advection throughout the day. Models indicate low
level thicknesses during mid afternoon about 50 meters down from
Wednesday afternoon...which translates to 10-15 degrees cooler. As
such, highs will edge above normal one final day...reaching around
60 northwest ranging to upper 60s in the southeast.
Seasonable high pressure over the central plains will build eastward
and the pressure gradient will relax Thursday night. Under clear
skies with the cool dry airmass in place, mins will tumble into the
30s over the area, with some locations in the north and
west potentially falling slightly below freezing near sunrise.
Near zonal flow aloft and reinforcement of the surface high with
modestly cooler air from the northern plains will maintain the
status quo with mostly sunny skies Friday and increasing high
cloudiness Saturday. Highs will be in the mid to upper 50s
Friday cooling to the low and mid 50s Saturday.
.LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/...
As of 252 PM Wednesday...
In the Sunday time frame...moisture advection out of the Gulf will
stream east along a frontal zone setting up across the Gulf States.
With a cool dry airmass in place, we should see a thickening
cloudiness Saturday night with light rain breaking out due to
isentropic lift in the west by mid day Sunday, and will maintain
ongoing chance PoPs in the west during the morning spreading over
the east during the afternoon. Highs will be subsequently suppressed
by clouds and evaporative cooling, ranging from mid 40s in the
northwest to lower 50s in the southeast.
The forecast from Sunday night onward remains low confidence pending
consensus as to the progression of a cutoff low over northern Mexico
which will be lifting ENE across the plains early next week.
Initially, the high pressure over the area is reinforced by the
arrival of a second surge of cool dry air from a transitory surface
high oriented more classically from New England south down the east
coast, which would suppress moisture southward on Monday. This would
set the stage for another isentropically induced rain regime on
Tuesday/Wednesday as the moisture associated with the aforementioned
cutoff low and associated surface reflection ride up the cooler
denser air. Will keep PoPs on the low chance side for now, with
highs in the 50s Monday through Wednesday as we wait to see how
the scenario plays out.
.AVIATION /21Z WEDNESDAY THROUGH MONDAY/...
As of 205 PM Wednesday...
MVFR ceilings in a low overcast across the Piedmont have largely
lifted with mainly scattered clouds at around 3kft and various BKN
clouds layers above. Further east and south, the low overcast has
been more stubborn with a predominance of BKN clouds at around
2.5kft. Mainly dry conditions with only isolated showers are
expected this afternoon before an eastward advancing cold front
pushes a band of showers and perhaps an embedded thunderstorm east
across central NC during the evening and especially the overnight
The front`s eastward progress has slowed today. The best chances
of showers along with ceiling and visibility restrictions range
from 22Z to 03Z at the KINT and KGSO terminals and from 02Z to 08Z
at the RDU/KRWI/KFAY terminals. Improving conditions with breaks
in the overcast and clearing skies will arrive behind the front
for the daybreak hours with VFR conditions in scattered cumulus
clouds expected on Thursday. Gusty south winds today will become
south-southwest this evening at 10-15kts with gusts of 20-30kts,
even stronger in any thunderstorm. The winds will become westerly
behind the front at 10kts and northwest at 10-15kts on Thursday.
Looking beyond the 24 hour TAF period... High pressure will build
into the region on Thursday and persist into Saturday resulting
in fair weather. A storm system will approach the area from the
southwest on Sunday with a chance of adverse aviation conditions
late sunday into Monday. -Blaes
Record highs for 11/30
RDU 77 2006
FAY 80 1927
GSO 74 1991
Record high minimums for 11/30
RDU 62 1934
FAY 62 2001
GSO 62 1934