Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC
FXUS62 KRAH 291954
Area Forecast Discussion
National Weather Service Raleigh NC
350 PM EDT THU SEP 29 2016
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.
.NEAR TERM /through tonight/...
As of 250 PM Thursday...
Flash flood watch for the far eastern and southeast sections of the
forecast area will continue for now, and may need to be extended in
area based on further assessment of developing convection. This
morning`s band of heavy rain and storms which instigated countless
flooding reports this morning was oriented along a band of strong
low level moisture transport, strong upper divergence, and focused
deep IVT, all of which have weakened and shifted eastward, along
with the greatest coverage of moderate to heavy rain. Bands of
showers and storms are developing once again over NC this afternoon,
pivoting around the KY upper level low, and while the strongest
storms are expected to be in the Triad region to the north and NW
(where deep layer bulk and effective shear is quite strong and where
low level lapse rates are approaching or exceeding 7 C/km) over the
next 6-8 hrs, a few strong storms are possible this afternoon into
early evening over the remainder of central NC with surface
dewpoints solidly in the upper 60s to lower 70s. Instability so far
has been marginal despite some insolation, but will continue to
monitor. Otherwise, still expect training cells given the band-
parallel cell motion, which could push local rain totals up to 2-3"
in spots, while many areas outside of such bands may see less than a
half inch. Locations which have seen considerable rainfall in the
last 24 hours cannot handle much more water and may see a rebounding
of flooding with even minor amounts of additional rainfall. Showers
and isolated storms will slowly decrease in intensity and coverage
later this evening and into the overnight hours with an expected
decrease in low level moisture transport, although the persistence
of upper divergence especially across the NE and far N CWA will
necessitate retaining a low chance there through the night. Areas of
fog and stratus should return late tonight. Lows from the low 60s
west to upper 60s east. -GIH
.SHORT TERM /FRIDAY AND FRIDAY NIGHT/...
As of 325 PM Thursday...
The large upper low will wobble and drift slowly northward over IN
during this period, while weak surface low pressure holds over the
far western Piedmont along the increasingly diffuse north-south
oriented surface front. This front will weaken further as it eases
just a bit eastward into central NC through the day, with the
greatest PW over the eastern fringe of the CWA and over coastal
sections. The bulk of the DPVA pivoting around the mid level low
appears to hold just to our west, while the better upper divergence
shifts just to our north and NW, so we should see a lessening of
both deep moisture and of large scale forcing for ascent. Will
maintain high chance pops across the far N and NE trending to slight
chance pops over the SW, decreasing after nightfall. Expect highs
from the upper 70s to lower 80s, followed by lows in the mid 50s
west to mid 60s east. -GIH
.LONG TERM /SATURDAY THROUGH THURSDAY/...
As of 350 PM Thursday...
The persistent upper low over the Tenn Valley will finally lift
north into the Great Lakes and weaken, as a trough deepens over the
Pacific Northwest. This will lead to a general trend toward higher
heights over the eastern U.S, a surface high pressure ridge down the
East Coast and temps near at or just slightly above. Before the low
fully departs the region, some diurnal convection is possible across
the far south/east Saturday and Sunday given the continued presence
of the front that sinks over the area this weekend, but with
diminishing in coverage with each day.
Most of the long term focus is with the uncertainty in the track of
what is currently Hurricane Matthew over in the Central Carribean.
The official NHC track brings Matthew north across the Bahamas early
next week in response to an upper trough cross the Gulf Coast
region. This is still rather uncertain at day 7, however, and quite
likely to change in the coming backs.
.AVIATION /18Z THURSDAY THROUGH TUESDAY/...
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
Flash Flood Watch until 10 PM EDT this evening for NCZ028-042-043-