Area Forecast Discussion
Issued by NWS Wilmington, NC-- Remove Highlighting --
-- Discussion containing changed information from previous version are highlighted. --
FXUS62 KILM 251741
Area Forecast Discussion
National Weather Service Wilmington NC
141 PM EDT Sun Sep 25 2016
A cold front will stall across South Carolina tonight before
returning north Monday. A stronger cold front will move across
the Carolinas Wednesday or Thursday. Behind this next front,
drier and cooler weather will arrive on northerly winds.
.NEAR TERM /THROUGH TONIGHT/...
As of 1230 PM Sunday...Enough sun has finally made it through the
low clouds across NE North Carolina and coastal South Carolina to
fragment them and lift cloud bases substantially. The latest HRRR
still isn`t excited about rainfall potential, however the new 12z
synoptic models (GFS and NAM) still show that potential later this
afternoon, especially from just west of Wilmington to near Conway,
a short distance behind the frontal position. Minor tweaks have
been made to forecast highs. Discussion from 945 AM follows...
The cold front slipped through Wilmington before sunrise but is
decelerating as it pushes farther southwestward. Northeasterly
winds both ahead and behind the front are making it tough to find
the exact frontal location, but it appears at 9 AM to run from
Bennettsville and Dillon to Whiteville and Southport. Overnight
radiational cooling out ahead of the front produced widespread
fog, some quite dense, which is slowly burning off across coastal
South Carolina up through Marion into Lumberton. Post-frontal low
stratus has built into the Maxton- Lumberton-Elizabethtown area
but has remained north of Wilmington.
With the front almost stalling during peak diurnal heating this
afternoon, look for scattered showers and thunderstorms to develop
near or behind the front. That`s not normally how fronts work in
this part of the country, but in this case the front is bringing
in deeper moisture from the Atlantic, making the best precip
chances behind the front. SBCAPE rises to 500-1000 J/kg and
convective capping falls to 0-10 J/kg. The latest several HRRR
runs aren`t all that impressed with shower chances this afternoon,
but I am not going to remove the 20-30 PoPs in the forecast. Cell
motion should be very slow from north to south.
Highs today should range from the upper 80s in the Pee Dee Region
(a 90-degree reading is even possible west of Florence) down to
the lower 80s on the NC beaches. The 06z NAM looks to have a
better synoptic handle on the frontal position and temperatures
than the GFS.
.SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/...
As of 300 AM Sunday...High pressure across New England will drift
offshore and this will allow the cold front to push back N of the
area during the day with surface winds turning onshore and
eventually to the SE Mon afternoon and eve. A subtle mid-level
shortwave will sneak up the coast late in the day Mon and Mon night.
A vigorous trough carving out across middle America is expected to
drive a cold front into and eventually through the eastern Carolinas
Tue night or Wed. Moisture will increase steadily during Tue and Tue
eve and then begin to drop off sharply with frontal passage
overnight, lastly along the coast Wed. Will show convection through
the period, but include the highest probability Tue afternoon and
Highs will be about normal, lower 80s. Lows will be in the upper 60s
to lower 70s Mon night and then cooling in the wake of the cold
front to mid and upper 60s.
.LONG TERM /WEDNESDAY THROUGH SUNDAY/...
As of 300 AM Sunday...Deep upper low will evolve across the Great
Lakes and then sink slowly SE through late week before ejecting into
Canada during the wknd. This will drive a cold front across the
Carolinas on Wednesday, but its overall progression is a low
confidence forecast due to model uncertainties into the evolution of
the aforementioned upper low. ECM is deeper and stronger with this
upper low, cutting it off entirely from the mean flow into next
wknd. The CMC is the fast solution with short cutoff followed by
rapid progression into the westerlies by late week. The GFS is a
decent compromise, although its ensembles show a very large spread
by D6. The biggest difference to the sensible weather from these
solutions revolves around precip potential, as temperatures will
likely be seasonable or slightly below regardless of which outcome
Will favor the GFS attm which is supported by WPC, which
suggests the front will push offshore as the upper low begins to
move NE Thursday, with cool high pressure building down the coast
thereafter. Temperatures Wed/Thu will likely be around seasonable
norms or slightly above, but clouds and showers will be likely as
the front drifts towards, and then off, the SE coast. As the high
builds south late week and into Saturday, temps will cool to below
normal with mins potentially dropping to 60 or below, especially
inland, by the end of the period. If the ECM solution ends up being
correct, temperatures will still follow this trend, but both Friday
and Saturday could also feature periods of showers instead of the
drier forecast currently being shown.
.AVIATION /18Z SUNDAY THROUGH FRIDAY/...
-- Changed Discussion --As of 17Z...Favored a blend of the models for this period with
more confidence in the NAM and GFS then the ECMWF due to the
handling of the H5 low across the nrn portion of the country
during the next few days. Cold front south of KILM and KLBT at
this time and right near KCRE/KMYR/KFLO. Predominately northeast
flow and MVFR conditions are expected with mention of vcsh along
the coastal terminals but will leave out mention inland. HRRR a
bit overdone with the pcpn potential across the region but as
mentioned in the near term forecast best chances for pops are just
behind the front so that is enough reason for the vcsh. BUFKIT
seems to agree with this scenario as well with pcpn ending around
00z across the coastal terminals. Moderate confidence in MVFR due
to ceilings during the overnight period with improvement to vfr
after daybreak. Winds will stay up along the coast but I will
lower across KLBT and KFLO overnight.
EXTENDED OUTLOOK...Chance for SHRA/TSRA each day through Wed.
Otherwise expect VFR.
-- End Changed Discussion --
NEAR TERM /THROUGH TONIGHT/...
As of 1230 PM Sunday...The front is still making some progresses
southward down the SC coastline, with breezy NE winds in its wake.
Seas are still building in-line with our previous forecast and no
changes are necessary with this early-afternoon near term update.
Discussion from 945 AM follows...
A cold front has pushed as far south as Cape Fear this morning,
and should crawl southwestward along the South Carolina coast this
afternoon. Northeasterly winds are in place both ahead of and
behind the front, making wind speed and air pressure the best
determining factors for locating the actual front. Northeast winds
should increase to a solid 15 knots with gusts to 20 knots today,
strongest in the Cape Fear vicinity. Seas already as high as 3.5
to 4 feet north of Cape Fear should build to 4-5 feet near and
north of Cape Fear this afternoon, 3-4 feet along the SC coast
later this afternoon. Isolated showers or t-storms could develop
this afternoon in the Cape Fear to Myrtle Beach vicinity, but most
should remain inland.
SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/...
As of 300 AM Sunday...High pressure across New England will move
offshore and this will allow winds to shift from NE and ENE Mon
morning to E Mon afternoon and to SE Mon night. As a cold front
approaches the waters, SE winds Tue will become S and SW Tue
night. If the front does not slow down, winds may shift to the N
as early as the wee hours of Wed morning. The highest winds this
period will be Mon and Mon eve, up to 10 to 15 kt. Seas of 3 to 4
ft Mon and Mon night will subside to 2 to 3 ft Tue and Tue night.
LONG TERM/WEDNESDAY THROUGH THURSDAY/...
As of 300 AM Sunday...Some uncertainty exists in the extended with
respect to the timing of a cold front moving across the waters, but
attm it appears the front will stall over the waters Wednesday and
then shift well offshore during Thursday. This leaves a period of
highly variable winds on Wednesday with speeds of 5-10 kts, before
the front moves away Thursday followed by N to NE winds of 10-15
kts. Seas Wed and most of Thu will be 2-3 ft with residual 11-12 sec
swell remaining in the spectrum combined with low-amplitude wind
waves. Late in the period a northerly 4-5 sec wave will amplify, and
seas may build towards 3-4 ft late Thursday.