Area Forecast Discussion
Issued by NWS Wilmington, NC-- Highlight Changed Discussion --
-- Discussion containing changed information from previous version are highlighted. --
FXUS62 KILM 211414
Area Forecast Discussion
National Weather Service Wilmington NC
1014 AM EDT Fri Apr 21 2017
Bermuda High pressure will extend west across the region through
early Sunday. A backdoor cold front is expected to stall north
of the area during the weekend. Strong low pressure will move
slowly through the Carolinas Sunday and Sunday night and then
offshore Monday. Widespread rainfall is expected along with the
possibility of strong to severe thunderstorms. This system will
then move slowly away from the area as high pressure and dry
weather builds in for the middle and later portions of next week.
.NEAR TERM /THROUGH TONIGHT/...
As of 1000 AM Friday...High pressure has sunk a little farther
south over the past 24 hours, increasing the degree of westerly
flow across the Carolinas. 12z soundings from both CHS and MHX
had 850 mb temps of +14C, near the 90th percentile for the
date. Very few changes are needed to the high temperature
forecast today which features upper 80s everywhere more than 10
miles inland, with highs close to 80 expected on the beaches.
These warm temperatures should help drive a strong seabreeze
circulation this afternoon. This is probably the biggest change
to the forecast as sustained surface winds should reach 20 mph
with gusts near 30 mph during the mid to late afternoon at the
beaches. Marine MOS guidance for wind speeds at JMPN7
(Wrightsville Beach) and MROS1 (Myrtle Beach) indicates this
potential very well. The initial movement of the seabreeze
boundary will probably be quite slow as deep westerly flow
holds the boundary close to the beaches from noon through 3 PM.
The airmass aloft has dried out a little more than yesterday,
and despite very warm temperatures and computed surface-based CAPE
as large as 1200 J/kg I don`t expect many of this afternoon`s
cumulus will be able to produce showers. If a brief shower does
develop the HRRR has been focusing on the Bennettsville to
Lumberton corridor for its past few runs. The Piedmont Trough
and Sandhills-to-Piedmont differential heating does tend to
focus convective activity along this corridor, but the
probability of rain is still too low to include today. The dry
forecast will continue.
Much like last night a moderate low level jet should develop
after sunset with 1000 foot winds increasing to 25-30 knots.
This mechanically-forced mixing should help keep the boundary
layer temperatures from diving too deep, and lows should reach
the mid 60s with some upper 60s at the immediate coast.
.SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/...
As of 300 AM Friday...Warm ridge will get suppressed to our S
and E Sat as a cold front struggles to backdoor through North
Carolina. This front still looks as though it will get hung up N
of our Forecast Area during the first half of the weekend.
Upper low across the mid south Sun morning is now expected to
take a southeast track and on this path will move across the
southern Appalachians late Sun night and Mon morning. The
surface low will move slowly across the Carolinas Sun and Sun
night and should be moving offshore of the Carolinas Mon
Forcing is weak Sat, and moisture is shallow. Mixed layer CAPE
values do climb to or just above 500 J/kg and so isolated
showers and thunderstorms will be possible with the highest POPs
from LBT to Burgaw, in closest proximity to the frontal zone.
Attention then turns to system to our W and this promises to be
a wetter scenario for the eastern Carolinas with strong lift
developing later Sun and Sun night. Precipitable water values
will climb to more than one and a quarter inches as the depth of
moisture deepens. Mixed layer CAPE values are expected to reach
500 to 1000 J/kg. Thus, the area will have all of the necessary
ingredients for showers and thunderstorms. Will show POPs
increasing to categorical. At this time, rainfall amounts of one
half to one and a half inches seems attainable. There still is
some risk for strong to NE...severe thunderstorms and the track
of the surface low will be important in determining where this
risk will be highest. Bulk shear values and winds within 5 kft
of the surface are quite marginal and do not support widespread
severe weather. Model consensus would suggest the risk for
severe weather will be higher across our southern counties and
Temps will be well above normal, warmest Sat and coolest Sun
.LONG TERM /MONDAY THROUGH THURSDAY/...
As of 300 PM Thursday...The sfc low center should be just over
or near the Cape Fear coast Mon morning, but the deep upper
level trough will still be west. The cutoff low center will
track mainly south of the area but the trough will extend up
through the Carolinas. The low will move east through the day on
Mon and then will travel slowly N to NE parallel to the coast.
This will keep clouds and rain chances in the forecast possibly
through Tues. Should see drier conditions by mid week as weak
high pressure builds in behind departing low.
Temps should be a good 10 degrees cooler on Monday in northerly
flow on the back end of the low. Clouds and rain will keep
smaller diurnal ranges with temps heading back toward normal
Tues into Wed as low slowly departs. Overnight lows will
probably be 55 to 60 most places. Temps should be back up into
the 80s by mid week with increasing sunshine.
.AVIATION /12Z FRIDAY THROUGH TUESDAY/...
As of 12Z...High confidence in VFR conditions through the
valid TAF period. SW winds will be on the breezy side today
with the potential for gusts in excess of 20 kt, especially
along the coast. The seabreeze will back winds to SSW at KCRE
and KMYR. Cannot rule out an isolated afternoon shower but the
chance a terminal would be impacted is extremely low. Any
diurnal clouds that manage to develop will dissipate around
sunset. Winds above the boundary layer of 25 to 35 kt will
preclude any late night fog possibility.
Extended outlook...MVFR/IFR conditions possible in showers and
TSTMS, mainly Sun through Mon. Otherwise VFR.
NEAR TERM /THROUGH TONIGHT/...
As of 1000 AM Friday...Bermuda High Pressure has sunk a little
farther south over the past 24 hours, and will continue to
control the weather today and tonight. With inland temperatures
soaring well into the 80s a strong seabreeze circulation should
develop this afternoon with wind speeds by 3 PM increasing to a
solid 20 knots near the beaches. The limited area of stronger
winds will create very choppy conditions across the nearshore
waters, but overall seas should not rise much beyond 3 feet.
A low level jet developing again tonight should help keep wind
speeds in the 15-20 kt rain almost up through daybreak Saturday.
Seas could build to 3-4 feet, particularly away from shore
tonight. Dry weather will continue.
SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/...
As of 300 AM Friday...Ridge of high pressure will be offshore
at the start of the period. A cold front to our N will be strung out
W to E and will struggle to make southward progress. This front is
expected to stall out before reaching any of our waters Sat
night. A strong area of low pressure and its associated frontal
system will approach from the W Sun and move slowly across the
waters Sun night into Mon, bringing widespread convection. SW
winds will persist Sat into Sun. These winds will be strongest Sat
afternoon and Sat night, sustained at 15 to 20 kt. Winds will back
slightly on Sun, SSW to S. Late Sun night and Mon morning, the wind
direction will back all the way around to NE. Seas will build up to
3 to 5 ft through Sat night with seas holding near this range
through Sun night before building further Mon.
LONG TERM /MONDAY THROUGH TUESDAY/...
As of 300 PM Thursday...Low pressure will be moving across the
waters Mon with a sharp shift in wind direction to the N on the
back end. The center of the low should be just near or south
of the Cape Fear coast Mon morning. The winds may diminish and
become quite variable at this time before the low slowly moves
east and north through late Mon into Tues. This should allow
seas to diminish for a brief period Mon morning before a sharp
rise in northerly surge on the back end. Winds may increase up
to 15 to 25 kt Mon into Mon night before diminishing through
late Tue as the low tracks farther away. Seas may remain above
SCA late Mon into Tue, diminishing Tue night in a lighter