Area Forecast Discussion
Issued by NWS Wilmington, NC

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FXUS62 KILM 302310
AFDILM

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

.SYNOPSIS...
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.

&&

.NEAR TERM /THROUGH MONDAY/...
As of 730 PM Sunday...Small tweaks were made to temps, sky cover
& dewpoints with this early evening update. No significant
changes in forecast thinking over the coming 24 hours as
unseasonably warm weather continues. Discussion from 300 PM
follows...

Water vapor imagery this aftn is impressive with a deep cyclone
spinning across OK/KS and its moisture tap spawning impressive
convection across the Gulf Coast ahead of a surface cold front.
Locally, a weak mid-level impulse is moving across SC with very
dry and large high pressure spinning just offshore.

The offshore high pressure and aforementioned approaching cold front
are driving increasing moist southerly flow today, and dewpoint
values remain a degree or two either side of 70. Despite the very
high dewpoint temperatures, moisture is confined to the lowest 4 kft
or so of the column, with forecast profiles exhibiting extremely dry
air above 850mb. This is allowing for the widespread CU from earlier
this morning, which is now eroding slowly as mixing taps into the
drier air aloft. A few isolated showers have developed within the CU
today, but have since faded as they entrained this dry air. The
exception to this has been well inland where weak PVA within the mid-
level vorticity max moving overhead a region of better PWAT as noted
on SPC Mesoanalysis to produce scattered showers. Have maintained
just SCHC POP for inland zones, highest west of i-95 through this
evening. This activity is expected to dissipate with loss of heating
after sunset, and with very dry air aloft convection will remain
just showers - no lightning expected.

Temps today in the mid 80s will cool only very slowly as southerly
winds increase in response to the tightening pressure gradient. Have
forecast mins above all available guidance, and lows will drop only
into the low 70s as the coast, upper 60s well inland. The moist low
levels and gusty winds overnight will create another environment
favorable for stratus as well.

On Monday, the cold front will approach quickly from the west, but
the lion`s share of its impacts will hold off until Monday night
/beyond the near term./ However, the pinched gradient will drive
increasingly gusty southerly winds, especially during the aftn and
evening, with gusts over 30 mph likely across much of the area. POP
begins to ramp up in the evening as a line of showers and tstms
along the front advects eastward, and by Monday night the western
half of the CWA will likely be experiencing convection. SPC has
placed the area in a MRGL risk, but this appears to be mostly
focused for the overnight period. Very strong winds and shear
support storm organization with the convective line, and temps in
the low 80s will create at least marginal instability. With most of
the convection expected overnight, please refer to the short term
discussion below for more information on this severe risk
locally.

&&

.SHORT TERM /MONDAY NIGHT THROUGH TUESDAY NIGHT/...
As of 300 PM Sunday...A cold front will be on our western
doorstep at the start of the period and will move steadily east
through the CWA and offshore by about 12 UTC Tuesday morning.
We are advertising likely to in some cases categorical pops
which is higher than most numerical guidance. There are some
indications of the line becoming fractured which seems to be the
issue with the lower guidance values but still think most
places will measure but total QPF will be modest at best. Severe
threat still exists mostly toward the western areas where
timing (late afternoon and early evening) will be more conducive
for the convection to produce some strong wind gusts and hail.
SPC`s latest day two outlook has most of the area in a marginal
risk. A deep westerly flow develops in the wake of the front for
Tuesday through Wednesday morning with dry and warm conditions.

&&

.LONG TERM /WEDNESDAY THROUGH SUNDAY/...
As of 300 PM SUNDAY...High pressure and dry weather will continue
Wed and Wed night. Low pressure across the Gulf coastal states and
Tennessee Valley Thu is expected to reach the southern/central
Appalachians Thu night and then move slowly to the N Fri and Sat as
a vertically stacked system. The longwave upper trough is expected
to move east of the eastern Carolinas Sat with another spoke of
vorticity perhaps skirting the FA to the N Sun. Surface high
pressure will build from the NW beginning Sun. It should be noted
that although our forecast is aligned most closely with this
scenario, the models have offered very different scenarios and there
has not been good run to run consistency as of yet.

Currently, we have at least average confidence given the time range
we are forecasting for, that the risk for showers and thunderstorms
will increase in the warm sector Thu and Thu night. We will carry
the highest POPs, up to categorical, Thu night. Then, confidence in
the forecast drops below average for Fri and Sat. It is possible
that we will get dry slotted on Fri and convection will not be as
widespread as Thu night. However, with strong upper level support
still upstream and destined to rotate around the base of the trough,
and a surface cold front hanging to our W, believe at least
scattered if not numerous showers and thunderstorms will occur Fri
with lesser coverage Sat when this energy should be sweeping
offshore. Will keep POPs out of the forecast for Sun.

The risk for heavy rainfall given the magnitude and duration of deep
moisture return is high. This rain will be falling on soils that
were drenched last week and another quick round of convection will
bring additional rainfall early in the week. Thus, we will have to
watch for the potential for renewed flooding late week. Falling
river levels this week may reverse higher with the additional heavy
water load late week. The severe weather risk may also increase late
week, but it is still premature to offer any timing or threat
specifics at this time.

&&

.AVIATION /00Z MONDAY THROUGH FRIDAY/...
As of 00Z Monday...VFR conditions this evening should become
MVFR overnight as stratocumulus clouds with bases between
1500-2000 feet AGL develop. The best potential should exist
for the inland airports FLO and LBT, with lesser potential near
the coast. Wind speeds will increase just above the surface
overnight, and as the sun induces a deeper mixed layer to
develop Monday morning look for surface gusts of 30 knots to
come down to the surface with sustained wind speeds increasing
to near 20 knots. A line of showers and thunderstorms preceding
a cold front will sweep east across central South Carolina
during the afternoon hours and may reach the FLO and LBT
airports Monday evening as early as 23Z.

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

&&

.MARINE...
NEAR TERM /THROUGH MONDAY/...
As of 730 PM Sunday...Seabreeze winds were not quite as strong
this afternoon as they were the past two afternoons. Enjoy the
lull while you can because the synoptic pressure gradient will
begin to drive increasing wind speeds late tonight and into
Monday. No significant changes were made to the forecast with
this early evening update. Discussion from 300 PM follows...

High pressure offshore and a cold front approaching quickly
from the west will drive increasing southerly winds this period,
and the Small Craft Advisory has been shifted to begin earlier.
Winds this aftn have been south at around 15 kts, and these are
expected to steadily increase overnight and on Monday. While
the direction will remain predominantly from the south, speeds
will rise to 20-25 on Monday, with gusts up to 30 kts or higher.
These winds will be the primary driver of wave heights through
Monday, and seas will climb from 2-4 ft this aftn, to 4-7 ft
late Monday thanks to a forecast 7ft/7sec southerly wave. The
SCA for all waters has been moved up to begin at 6am Monday for
rapidly increasing winds, and will persist into the short term.

SHORT TERM /MONDAY NIGHT THROUGH TUESDAY NIGHT/...
As of 300 PM Sunday...A strong southerly flow of 20-25 knots will be
in place ahead of a cold front to the west initially. Speeds may
even increase a couple of knots over 25 for a few hours before the
front moves across between about 9-12 UTC Tuesday. A west to
occasionally southwest flow of 10-15 knots will develop in the wake
of the front and persist through the end of the period. Significant
seas will also be very high early on with the strong winds, six to
ten feet then fall dramatically during the day Tuesday.

LONG TERM /WEDNESDAY THROUGH FRIDAY/...
As of 300 PM Sunday...There is a likelihood for Small Craft Advisory
conditions later Thu through Fri night. Elevated seas may linger
into Sat.

High pressure will be weakening across the waters Wed into Thu. A
cold front associated with a slow moving area of low pressure to our
W Thu and Thu night should eventually push offshore late Fri or Fri
night. The wind direction will settle on SE Wed as high pressure
loses its influence. SE winds Wed night and Thu will veer to S
by/during Thu eve. S winds should veer to SSW and SW overnight Thu
and SW Fri. The strongest winds will likely occur Thu night into
Fri, up to 20 to 25 kt. Seas will build through the period, from 3
ft Wed, to 4 to 7 ft Thu afternoon and eve, and to 6 to 9 ft
Fri.

&&

.ILM WATCHES/WARNINGS/ADVISORIES...
SC...Beach Hazards Statement from Monday morning through Monday
     evening for SCZ054-056.
NC...Beach Hazards Statement from Monday morning through Monday
     evening for NCZ106-108-110.
MARINE...Small Craft Advisory from 6 AM Monday to 11 AM EDT Tuesday for
     AMZ250-252-254-256.

&&

$$

SYNOPSIS...SHK
NEAR TERM...TRA/JDW
SHORT TERM...SHK
LONG TERM...JDW
AVIATION...TRA



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