FXUS62 KILM 301720

Area Forecast Discussion
National Weather Service Wilmington NC
120 PM EDT Sun Apr 30 2017

High pressure will extend across the area from offshore through
early Monday with warm and humid conditions continuing. A cold
front will bring a likelihood of showers and thunderstorms late
Monday into early Tuesday. High pressure will follow for the
mid-week period. A Low pressure system will impact the region
Thursday into Friday and may bring widespread showers and
thunderstorms and heavy rain.


As of 1030 AM Sunday...Update to POP and SKY this morning, but
otherwise forecast remains on track. High pressure offshore and
its associated moist return flow has allowed Cu-streets to
develop, with some better bubbling along the sea breeze front.
Note some enhanced moisture in WV imagery across SC, likely
from a weak mid- level impulse as modeled by the latest NAM. The
combination of this impulse and dewpoints in the upper 60s to
low 70s will support isolated showers through this evening,
mainly along the southern part of the sea breeze and then
towards i-95 where better PVA will exist. Dry air in the mid-
levels will preclude much in the way of thunder, and as
dewpoints dry this aftn with mixing cloud cover should decrease.
Previous discussion below:

As of 300 AM Sunday...Light southerly flow continues with very
humid air mass over the area this morning. Winds slightly lower
than last night has allowed for some patchy fog. Moisture
profiles show a shallow saturated level once again below 1k ft.
Looking around at obs, many sites to the south and west of local
area were reporting decks of stratus right around 800 to 900
ft. Have included several hours of these low clouds into the
morning before they lift leaving some strato cu and cirrus
around this afternoon. Overall expect a fair amount of sunshine
this afternoon. Temps early morning will remain right around 70
degrees which will jump start the temps to continue well above
normal temps for today. Should see max temps in the mid 80s most
places. Although the temps will be running several degrees
above normal today, records will be tough to beat most places
except perhaps for North Myrtle Beach.

Record max temps around the area for today
Wilmington 92 set in 1974
North Myrtle Beach 83 set in 2007
Florence 94 set in 1981

Have included a brief period of very slight chc pops west of
I-95 this afternoon as the upper ridge begins to slip east
losing the strong cap aloft. A deep trough will drive a cold
front toward the Carolinas by Monday morning. Although the front
remains well west at the end of the this period, the gradient
will tighten and expect increasing winds through tonight. All
pcp associated with the cold front will hold off until Monday.
Soundings continue to show very shallow moisture in place once
again tonight but dewpoint temps seem a bit lower so not as
confident. Overnight temps will once again remain a good 10
degrees above normal in a unseasonably warm and humid air mass.


As of 300 AM Sunday...Chances for convection increase on Monday
as a cold front moves east across the coastal Carolinas as an
upper trough transits across eastern CONUS. High pressure over
the western Atlantic will retreat east as the cold front
approaches, with spotty late afternoon convection increasing
into the likely category from west to east Monday evening as the
front moves across the forecast area. A consensus of guidance
has the precip well offshore by daybreak on Tuesday. Post-
frontal airmass is very dry and a bit cooler. Steady SW flow in
advance of the front will maintain above-normal temperatures on
Monday, with highs in the lower to mid 80s and lows in the lower
to 60s. Tuesday will be a bit cooler although still above
normal, with highs of around 80 and lows in the upper 50s and
lower 60s.


As of 315 PM Saturday...High pressure will remain in place
Wednesday with slightly warmer temperatures but continued dry
weather before it shifts offshore Thursday. This occurs in
response to a deep mid-level trough digging into the middle of
the country and then evolving across the eastern CONUS into the

There exists two distinct camps in the guidance: the GFS has
this low cutting off and dropping southeast through the end of
the period. The CMC/ECM have a similar pattern initially to the
GFS, but the upper low drifts north before cutting off over the
Northeast. The biggest difference between the guidance appears
to be the evolution of the ridge across the middle of the
country. The CMC/ECM keep the ridge axis aligned N/S, while the
GFS produces a more tilted NE/SW ridge which suppresses the
upper low. The agreement between the ECM/CMC tends to favor that
solution a bit more, despite the fact that the GFS has been
consistent and we had a similar setup just last week so there is
precedent. The evolution of this upper pattern is critical
because, while all scenarios support showers and thunderstorms
late Thursday and Friday, the CMC/ECM would dry things out for
the weekend, while the GFS would maintain unsettled and possibly
very wet weather for several days. Without a clear solution at
this time range, will hedge with a WPC favored blend of guidance
but with a bit more weight on the drier ECM by the weekend.
This would also bring much cooler temperatures to the region
Fri/Sat with highs and lows falling below climo.


As of 18Z...High pressure offshore and a cold front approaching
from the west will keep a moist southerly flow across the area
through the valid period. These southerly winds will steadily
increase from around 10-15 kts today, to 15-20 kts tonight and
Monday, with gusts of 20-30 kts likely beginning late tonight.
These winds will continue to advect moisture into the area as
well, so SCT/BKN diurnal CU at MVFR/VFR levels will persist. A
few showers are possible as well, but are expected to be
isolated and transient enough to neglect any TAF mention. If any
site were to receive rainfall today it would most likely be
FLO, and will handle with any AMD`s as required. Any showers
will erode tonight but stratus is expected to redevelop.
Forecast profiles suggest primarily MVFR stratus, but have added
some TEMPO IFR both for persistence from the previous nights
and to account for numerical guidance suggesting IFR. Stratus
will lift after sunrise on Monday.

Extended outlook...Periods of IFR/MVFR conditions are possible
in showers and thunderstorms late Monday into early Tuesday, and
again late Thursday through Friday.


As of 300 AM Sunday...Southerly return flow will continue around
high pressure well offshore. Expect winds 10 to 15 kts today
with an uptick due to sea breeze in the aftn where gusts could
reach over 20 kts. By tonight the gradient will tighten as a
cold front nears the Carolinas from the west. Expect winds to
increase up to 15 to 20 kts with higher gusts after midnight.
This will drive seas up from 2 to 3 ft today to 3 to 5 ft after
midnight and could possibly see a few 6 fters by Mon morning.
Precautionary conditions will exist after midnight tonight with
a small craft advisory launched for after this period.

As of 300 AM Sunday...Increasing SW flow in advance of the next
cold front has prompted the issuance of a Small Craft Advisory
for Monday afternoon and night. By Monday night seas will have
built to 4 to 7 ft, although winds may slacken in the pre-dawn
hours of Tuesday as the front makes its close approach to the
waters. Expect SCA to be short- lived as post frontal surge will
be modest and offshore, with seas decaying back before 6 ft by
Tuesday afternoon.

As of 315 PM Saturday...A secondary surge flips winds around to
the NW by Wednesday at less than 10 kts. As the high shifts
offshore into Thursday, southerly winds will ramp up quickly
becoming 15-25 kts, driving seas back to 4-7 ft after being just
2-3 ft much of Wednesday. An SCA will likely be needed
beginning late in the extended.


MARINE...Small Craft Advisory from noon Monday to 8 AM EDT Tuesday for



NWS ILM Office Area Forecast Discussion