Area Forecast Discussion
Issued by NWS Wilmington, NC-- Highlight Changed Discussion --
-- Discussion containing changed information from previous version are highlighted. --
FXUS62 KILM 211711
Area Forecast Discussion
National Weather Service Wilmington NC
111 PM EDT SAT MAY 21 2016
Showers and thunderstorms are possible ahead of a cold front
today. An upper low will keep conditions cool with a slight
chance for showers through Monday. More summer like weather
develops by the middle of next week with above normal temperatures
and drier conditions.
.NEAR TERM /THROUGH TONIGHT/...
-- Changed Discussion --As of 1230 PM Saturday...the mid-level s/w trof mainly responsible
for the rain this morning, has accelerated well ne of the area.
in its wake, weak subsidence aloft will keep a lid on convection
atleast thru the mid-afternoon hrs. Daytime insolation has broken
thru to the sfc...with the ovc stratus cloudiness having
transitioned into a cu field across the Carolinas. This will lead
to increasing sfc based instability with Nambufr Soundings
indicating 2000+ CAPE by late this aftn and into the early
evening, along with DCape values increasing to 800+. SFC forcing
from a cold front dropping southward will provide the necessary
forcing to help initiate convection. The time frame for this to
occur will be from late this afternoon thru the mid evening hours
with 30-40 pops covering it. Looking over the various thunderstorm
parameters, the best potential these storms produce will be for
strong wind gusts and have re-hashed and highlighted the hazardous
weather outlook to convey this potential.
Afternoon highs should break into the 80s across most locations
even along the immediate coast where westerly winds aloft will be
strong enough to keep the sea breeze pinned if its able to
develop. Tonights lows will depend on how much caa occurs behind
the front. Leaned toward the higher low temp mos guidance.
-- End Changed Discussion --
.SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/...
As of 300 AM Saturday...Upper level low pressure Sunday morning
across Pennsylvania will not move east as one might expect.
Instead, building 500 mb heights across the Great Lakes and
southern Canada will force this low to drop southward all the way
into northeastern North Carolina Monday morning. This will
unfortunately bring a great deal of cold mid and upper level air
southward (500 mb temps as low as -20C at ILM on the 00z GFS run)
which when exposed to residual low level moisture and strong May
sunshine will yield convective clouds and scattered showers. These
showers are expected to be most numerous Sunday afternoon with
forecast PoPs around 40 percent at ILM, 20 percent at FLO. Drier
air should limit shower potential further on Monday, and by Monday
night the upper level low should be far enough offshore for no
impact on our weather.
Temperatures will run several degrees below normal both day and
night through the period. I have generally used a MOS consensus
forecast which is little changed from the previous forecast.
.LONG TERM /TUESDAY THROUGH FRIDAY/...
As of 300 AM Saturday...Upper low moving away from the area Tue
will leave a flat mid level pattern over the region for the middle
of next week. Tue is a transitional day with surface high moving
overhead and shifting offshore as the 5h low exits to the
northeast. Temperatures will be near climo with deep west to
northwest flow keeping the region dry. Guidance is hinting at weak
ridging aloft trying to expand north from the Gulf or Mexico
midweek, pushing temps above climo Wed through Fri. Despite the
westerly flow aloft both the GFS/ECMWF show moisture from the
southwest topping the weak ridge and heading east late in the
week. Lack of deep moisture and weak subsidence will keep the
region dry Wed but the increased moisture late in the week and
potential for shortwaves emerging from the southwest does warrant
a silent pop Thu/Fri.
.AVIATION /18Z SATURDAY THROUGH THURSDAY/...
As of 12Z...Slow moving frontal boundary will keep much of the CWA
in showers this morning...with an isolated embedded rumble possible.
Coastal terminals could see some dense fog through about
13Z...slowly improving after that. Most of the convection will
exit the coast by 15Z...however if we get good solar
isolation...more convection is possible this
afternoon...particularly along the coast. Improving conditions this
evening...however the cold air advection will probably not begin
until the end of the forecast period.
Extended Outlook...Possible MVFR conditions on Monday, otherwise VFR.
-- Changed Discussion --NEAR TERM /THROUGH TONIGHT/...
As of 1230 PM Saturday...The main band of pcpn has pushed well ne
of the area with only isolated convection possible this aftn.
Expect convection to move off the mainland late this afternoon
thru this evening in response to a cold front, currently draped e
to w across northern nc, drops southward. Isolated tstorm wind
gusts could reach 30 kt. the cfp will occur from n to s...and
should be thru thru the ilm nc and sc waters by daybreak sun.
the sfc pressure pattern this aftn and evening will yield mainly
westerly winds, becoming nw-n later this evening and overnight as
the cold front drops south. The sfc pg is relatively weak with 10
to 15 kt wind speeds thru the period as a result.
Significant seas will run 2 to 4 ft...with dominating 6 to 8
second periods. The 4 footers will primarily occur across the ILM
NC waters from Cape Fear northward.
SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/...
As of 300 AM Saturday...Mainly northerly winds are expected
behind an early morning cold frontal passage Sunday. Low pressure
will develop along this front off the Virginia coast late Sunday,
and this should maintain a tight enough pressure gradient for 15
knot wind speeds to occur locally through Monday. By Monday night
high pressure over the midwest should move close enough to the
Carolinas to knock winds down below 10 knots.
LONG TERM /TUESDAY THROUGH WEDNESDAY/...
As of 300 AM Saturday...Surface high sliding off the coast Tue
will commence an extended period of south to southwest flow.
Gradient remains weak with speeds on the low end of the 10 to 15
kt range. Along the immediate coast there will be potential for a
sea breeze each afternoon, resulting in onshore flow around 15 kt
each afternoon along the coast. Seas around 2 ft through the
period with occasional 3 ft possible.
-- End Changed Discussion --