Area Forecast Discussion
Issued by NWS Wilmington, NC-- Highlight Changed Discussion --
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FXUS62 KILM 201220
Area Forecast Discussion
National Weather Service Wilmington NC
820 AM EDT SAT AUG 20 2016
Showers and thunderstorms are expected through the weekend as an
upper trough moves north of the area. Above normal temperatures
are expected Sunday with heat index values exceeding 100 degrees.
A cold front will cross the Carolinas Sunday night into Monday.
Much cooler and drier air will follow this front for much of the
.NEAR TERM /THROUGH TONIGHT/...
As of 630 AM Saturday...The Westerlies have dropped into the
Carolinas as a trough, currently digging through the Dakotas this
morning, moves eastward across the northern United States. The
Atlantic ridge has weakened and is now centered near the northern
Bahamas at the surface and 500 mb.
A stream of deep moisture originating over Texas has been entrained
into our westerly flow and will move across the Carolinas today.
After 1-2 PM the moderately unstable airmass (CAPE 1500-2000 J/kg)
and eroded convective cap should yield scattered showers and
t-storms. 700 mb wind speed around 20 knots should push the
developing thunderstorms quickly eastward, covering a lot of
ground even if a limited number of convective cells develop.
Precipitable water values up to 2.25 inches should help feed the
potential for heavy rainfall. Forecast PoPs have are 50-70 percent,
highest near the coast in the Myrtle Beach-Wilmington-Burgaw
corridor between 2-5 PM. This is reduced a bit from the 300 AM
forecast package as last night`s storms have developed into an
expansive MCS offshore which may induce subsidence over land
today, especially if the MCS persists to noon.
There is no organized convective risk forecast from SPC, although
with such high precipitable water values and the potential for
deep convection, a wet microburst cannot be ruled out.
Convective activity should diminish quite a bit by sunset as the
airmass will have overturned and subsequently stabilizes. A very
moist westerly flow aloft will continue, and it`s not impossible for
isolated showers and t-storms to linger overnight (elevated
instability) along any deeper boundaries left over from daytime
.SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/...
As of 300 AM Saturday...The upper trough will move east across the
Great Lakes Sunday and through New England Sunday night. The tail
end of the upper disturbance never reaches as far south as the
Carolinas, and in fact a careful look at our 500 mb heights show
they actually climb a bit through the period as the Atlantic ridge
begins to regroup.
Surface low pressure moving eastward concurrently with the upper
system will push a cold front southward and into the Carolinas
Sunday. Models have been bouncing around over the past few days with
the anticipated timing of the frontal passage, but the 00z GFS and
ECMWF are now targeting Sunday evening as when the front will
finally reach the coast. Winds are expected to shift to the north
behind the front by midnight Sunday night with drier and cooler air
streaming in for Monday and Tuesday.
Scattered showers and t-storms may develop Sunday in the warm and
humid prefrontal airmass. However once the front pushes through and
modified Canadian air begins to stream in, convective chances should
plummet Monday. By Monday evening there should be such little
moisture present (precip water down to 0.75 inches) that forecast
PoPs are below 10 percent. This appears to be the coolest airmass
we`ve seen in nearly two months, with lows Monday night and Tuesday
night expected to dive into the 60s away from the beaches.
.LONG TERM /TUESDAY THROUGH FRIDAY/...
As of 300 AM Saturday...A refreshing break from the heat and
humidity is expected for the upcoming week as cool high pressure
ridges down the east coast beginning Tuesday. Cold front will be
south of the area to start the period, with high pressure becoming
centered across the Mid-Atlantic and extending across most of the
eastern CONUS. Cool N/NE flow will be reinforced Tuesday night, and
although mid-level heights begin to rise quickly, low-level
thicknesses remain cool, and the Tue/Wed/Thu timeframe will feature
slightly below climo temperatures for the first time in quite a
while. It is looking more likely that the streak of consecutive days
at Wilmington not dropping below 70 will end on Tuesday, with at
least 3 nights next week featuring mins in the 60s, with highs in
the mid 80s. Accompanying these cooler temperatures will be some
very dry air, PWATS around 1 inch or less, only subtly recovering
Friday as the high pressure shifts offshore. The forecast is dry
through the period.
.AVIATION /12Z SATURDAY THROUGH WEDNESDAY/...
-- Changed Discussion --As of 12Z...Potential for brief MVFR/IFR in any heavy
downpours today and again late overnight into the early morning
hours due to areas of fog/low cigs. Otherwise expect VFR through
the valid TAF period with VCSH/VCTS.
Patchy fog and lingering low cigs are creating MVFR at KLBT
this morning. Expect these conditions to improve within the next
hour or two, allowing for VFR to prevail across the entire
forecast area through the rest of this morning. Along with
southwest winds increasing to around 10 kts today, anticipate
increasing coverage of scattered showers and thunderstorms, which
may create brief periods of MVFR/IFR, especially in heavier
downpours. Tonight, convection will gradually taper off with
winds becoming light for the overnight hours. Latest guidance
suggests areas of fog inland, which may create periods of MVFR
towards the end of the forecast period.
EXTENDED OUTLOOK...Potential for MVFR/IFR due to afternoon
showers and thunderstorms and overnight fog/low cigs potential.
Otherwise expect VFR.
-- End Changed Discussion --
NEAR TERM /THROUGH TONIGHT/...
As of 630 AM Saturday...High pressure located near the northern
Bahamas will move very little today. Low pressure moving east
across the Dakotas this morning will enter the Great Lakes by this
evening. This low will eventually push a cold front into the
Carolinas, but for today and tonight a west-southwesterly wind
should continue. Overnight thunderstorms have moved into the
offshore waters, but a second round of thunderstorms should
develop this afternoon and this evening as mid-level winds become
quite strong out of the west.
Seas are currently 2-3 feet mainly in 4-5 second wind chop.
Southwest winds increasing to near 15 knots late tonight may build
seas toward a solid 3 feet across open waters late.
SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/...
As of 300 AM Saturday...Surface low pressure will move across the
Great Lakes Sunday and into SE Canada Sunday night. This low will
push a cold front southward and into the Carolinas. Models have
bounced around quite a bit over the past few days with their
anticipated timing on the frontal passage. It now appears the
front should push out across the coastal waters Sunday evening,
with southwesterly winds shifting to the north at 15-18 kt.
Behind the front Monday the pressure gradient may be weak enough to
still allow the afternoon seabreeze to develop and turn nearshore
wind directions onshore. However when the sun goes down Monday Night
north-northeasterly surface winds should redevelop.
LONG TERM /TUESDAY THROUGH WEDNESDAY/...
As of 300 AM Saturday...Cold front will be south of the waters by
Tuesday morning, with high pressure expanding down the east coast
through mid-week. This creates a long duration of NE winds at
10-15 kts, lasting at least through this extended period. These
winds will drive an amplifying wind-wave which will be the
dominant wave group, with seas rising from 2-3 ft early Tuesday to
3-4 ft on Wednesday, and would not be surprised if some 5 fters
showed up late Wednesday. The exception will be in the typical
wave-shadow region SW of Brunswick county in AMZ252/AMZ254 where
NE winds get blocked, and seas will remain 1-2 ft.
As of 300 AM Saturday...The rain gauge on the North Myrtle Beach
ASOS clogged during a thunderstorm on Thursday August 18th. The
gauge measured 0.58 inches before the clog occurred. When our
technician cleared the blockage Friday morning, an additional 0.30"
poured through. This makes the CRE rainfall for August 18th 0.88
inches. (That`s 0.58 + 0.30) The Friday afternoon thunderstorm at
CRE only amounted to a trace.
Also, the streak of days with low temperatures 70 degrees or warmer
in Wilmington is approaching record territory. Counting through
midnight Friday August 19th we`re now at 54 days, a streak which
began back on June 27th. The all-time record is 56 days set back in
2012. To tie the record our temps will have to stay 70 or warmer all
the way through midnight Sunday night, and to break the record we`ll
need the same through midnight Monday night.
Note: Climate records are kept in local STANDARD time which is
actually 1 AM daylight time.