Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC-- Remove Highlighting --
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FXUS62 KRAH 291814
Area Forecast Discussion
National Weather Service Raleigh NC
215 PM EDT THU SEP 29 2016
-- Changed Discussion --A large upper level low will hold over Kentucky and southern Indiana
through Friday, as a surface front holds along the North Carolina
Foothills. The upper low will weaken and drift north and
northeastward over lower Michigan through the weekend, as the
surface front pushes slowly eastward across central North Carolina.
-- End Changed Discussion --
.NEAR TERM /TODAY AND TONIGHT/...
As of 1145 AM Thursday...
Have issued a flash flood watch for far eastern and southeast
sections of the forecast area through 10 pm this evening, although
much of this area is under ongoing flood warnings or advisories
anyway. A large area of 6-10" accumulations since yesterday
afternoon has led to significant flooding over portions of the
Sandhills and central/southern Coastal Plain. Additional convection
is a near certainty this afternoon, with nearly band-parallel cell
motions suggesting additional 1-3" are possible with locally higher
totals not out of the question, all of which would most certainly
exacerbate ongoing flooding. Next up is the potential severe threat
for much of the CWA. The 12z GSO sounding showed minor elevated
instability which would be fully released with heating, some of
which is taking place this morning with holes in the clouds
introducing enough insolation to push low level lapse rates up to 6+
C/km, with diminishing CINH. Deep layer effective shear is more than
sufficient at 40-50 kts, and projected MUCAPE of 1500-3000 J/kg this
afternoon added to the large scale lift generated by upper
divergence and DPVA around the large vortex over KY should prompt
strong to severe storm development by early to mid afternoon.
Little to no change to highs today, upper 70s to lower 80s. -GIH
Earlier discussion from 445 am... A busy midnight shift here in
central NC, one which began with a severe thunderstorm watch and
transitioned into a 100-year rainfall event (ongoing at ~09Z) across
portions of the Sandhills (i.e. Hoke/Cumberland/Harnett counties)
where as much as 5-8" of rain has fallen over the past 8-12 hours.
As such, the forecast discussion this morning will be brief. Several
SW-NE oriented lines of convection developed over central NC
yesterday afternoon/evening in assoc/w moderate diurnal
destabilization, low-level convergence attendant a pre-frontal
trough, and diffluent flow aloft downstream of a potent upper level
low. During the overnight period, rich low-level moisture assoc/w
southerly flow in advance of the approaching cold front has
maintained sufficient nocturnal instability for convection to
persist, resulting in significant rainfall and /potentially life-
threatening/ flooding across portions of Harnett, Hoke and
Cumberland counties this morning.
Although the cold front may make some slow eastward progress into
the area today, the parent upper level low will cut-off /stall/ over
the TN valley this aft/eve, and additional eastward progress of the
front is unlikely thereafter. As a result, expect a good chance of
convection again this aft/eve into tonight. A few severe storms
cannot be ruled out, and an isolated flash flood potential will
.SHORT TERM /FRIDAY AND FRIDAY NIGHT/...
As of 445 AM Thursday...
On Friday, expect conditions similar to Thursday with the upper
level low stalled over the Cumberland Plateau and the attendant cold
front stalled over central NC. -Vincent
.LONG TERM /SATURDAY THROUGH WEDNESDAY/...
As of 440 AM Thursday...
Stubborn upper level low over the Southern Ohio valley will lift
slowly north, back over the Great Lakes through the weekend. At the
surface, the lingering orphaned surface front will dissipate across
With Central NC on the eastern periphery of the deep cyclonic flow
and the back-edge of the deeper moisture plume (PWATS
~1.5")lingering over the coastal plain of NC, we`ll continue to see
a threat of mainly diurnal isolated to widely scattered showers
Saturday and Sunday, diminishing in coverage with each passing day.
Temperatures will continue to run slightly above normal with highs
ranging from upper 70s north to lower 80s south.
The closed low over the Great Lakes will finally open up and weaken
as it finally ejects eastward, moving off the New England Coast
Monday and into Tuesday. In it`s wake, sfc high pressure building
east and south down the Atlantic Seaboard will bring cooler, more
seasonable temperatures to the area by Tuesday/Wednesday.
Large uncertainty looms for the latter half of the upcoming work
week with respect to Tropical Storm Matthew. The NHC official
forecast has Matthew near Eastern Cuba Monday evening, with
questions as to whether Matthew will get picked up and directed
northward by an upper level trough over the Gulf of Mexico. Stay
tune and check with the National Hurricane Center for the latest on
Matthew. Users are reminded that the average NHC track errors at
days 4 and 5 are on the order of 180 and 240 miles, respectively.
.AVIATION /18Z THURSDAY THROUGH TUESDAY/...
-- Changed Discussion --As of 215 PM Thursday...
Conditions have improved to VFR over all but FAY, where MVFR cigs
lingered, and near GSO where MVFR cigs returned with showers in the
vicinity. Periods of sub-VFR conditions -- mainly MVFR but briefly
IFR at times -- is expected at all central NC terminal sites through
the rest of the afternoon, as scattered to numerous showers and
storms form over the area and move swiftly toward the north,
generating brief heavy rain, periodic wind gusts, and possible small
hail. The shower/storm coverage will slowly decrease through the
evening and night from SW to NE, with RWI the last to see the rain
threat diminish. With a moist ground and light winds from the SE,
widespread IFR to LIFR cigs and MVFR to IFR vsbys are expected to
develop at all sites after 07z tonight, lasting until around 13z
Fri. VFR conditions expected after that, through the end of the TAF
valid period. A few showers may linger through the morning in the
east near FAY/RWI.
Looking beyond 18z Fri, another round of MVFR showers and isolated
storms are expected mainly at RDU/FAY/RWI Fri afternoon into early
evening as a surface front shifts slowly eastward into central NC.
This front will weaken and dissipate heading into the weekend,
allowing the better rain chances to shift to our east. Except for a
potential for MVFR or IFR fog/stratus at RWI early Sat morning, VFR
conditions will dominate through Tue with low rain chances. -GIH
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Flash Flood Watch until 10 PM EDT this evening for NCZ028-042-043-