Scientific Forecaster Discussion
fxus62 kilm 240021
Area forecast discussion
National Weather Service Wilmington NC
821 PM EDT sun Jul 23 2017
a cold front will approach from the north tonight and Monday
and may slip into the area mid week before stalling and then
dissipating by Thursday. Showers and thunderstorms with heavy
rain will increase in coverage Monday through Wednesday and this
will serve to knock down the heat although the high humidity
will remain. Drier air may briefly work into the area Thursday,
but the arrival of a stronger cold front will bring more
thunderstorms by the weekend.
Near term /through Monday/...
as of 230 PM Sunday...many locations across the forecast area have
reached a heat index of 105f or higher with afternoon temperatures
in the lower to mid 90s and dewpoints in the mid to upper 70s.
Convection along the sea breeze has been suppressed thus far.
However, convection has fired far inland and a potential cold pool
may drive a more organized area of convection southeastward from
western NC. This feature would likely persist into the evening and
affect part of the Pee Dee per the latest hrrr. At any rate, plan on
focusing the highest pops across the Pee Dee and Lumberton areas
through the evening. Storm Prediction Center mesoanalysis dcape plot shows a swath of
>1000 j/kg across the Pee Dee and Lumberton areas. In addition, the
cape has swelled to 4000-5000 j/kg and subsequently the marginal
severe weather risk area has been expanded to include all of
northeast SC and southeast NC. The primary severe weather threat is
from damaging wind gusts, while some of these storms may be prolific
lightning producers as well.
Southwesterly flow will continue to pump warm/moist air into the
area through tonight with Bermuda high pressure in place. The mid-
level subtropical ridge will continue to break down across the
Carolinas as precipitable water values increase above 2 inches. This
will open the door to increased coverage in showers and
thunderstorms during Monday. The heat index will be tempered by
increased cloud cover and increased coverage of storms during
Monday. As a result a heat advisory is not planned for Monday at
Lastly, the new moon tides along with the persistent southwesterly
fetch (likely holding up water in the Cape Fear River basin causing
the half foot plus anomaly noted on the tide gauge) around the
Bermuda high will lead to another round of minor coastal flooding at
downtown Wilmington with high tide tonight. Plan to issue another
coastal flood advisory to account for the higher than normal water
Short term /Monday night through Tuesday night/...
as of 300 PM Sunday...mid to upper trough will move from the
Great Lakes to off the New England coast through the period.
This will push a cold front into the Carolinas by Mon eve and
down into our forecast area by tues morning and should end up
lingering right through our local forecast area into Wed. It
looks like the front will get strung out running from the
Atlantic waters off the New England coast down into the
southeast perhaps running right along the NC/SC border. Moisture
will pool ahead of this front with pcp water values up above 2
inches in deep SW flow along the coastal Carolinas. The trough
aloft will run right down along the southeast coast and will
need to follow exactly where the best upper dynamics will be to
focus main convective activity through the period. The latest
GFS shows our local area to be in a prime spot for enhanced
activity through tues while the European model (ecmwf) shows the best dynamics to
run a little farther south. Either way, this lingering front
and upper dynamics will produce plenty of clouds and convection
around through the period. The sea breeze should act to hold
front up or push it back inland with best convective activity
likely along the coast early and farther inland in the aftn to
The clouds and pcp will keep temps down closer to normal...around
90 for highs, but a few spots with breaks of sunshine could
spike up further. The humid air mass in place will combine with
heat to push heat index values up around 100. Overnight lows
will be in the mid 70s most places with slightly lower temps
tues night into early Wed as front drops south. Gusty SW winds
ahead of front will lighten as boundary drops south into the
area through tues. As flow lightens, the potential for flooding
will increase as storm movement will slow.
Long term /Wednesday through Sunday/...
as of 300 PM Sunday...the extended forecast period looks quite wet
as the ridge builds across the southern & central rockies and a
trough remains across the east. This seems to be a trend this
Summer which has so far featured very regular rainfall and soil
moisture values in the 70-90th percentile for the coastal Carolinas.
Wet soils may also be part of the reason why we haven't had any
extreme heat so far. The highest temps measured as far this year
include 95 in Lumberton and 96 in Florence. Both sites typically
have hit 100 by this late in the Summer.
A potent upper disturbance over South Carolina on Wednesday will sit
atop a stalled front and weak surface low pressure. Throw in
precipitable water values over 2.0 inches and cold enough
temperatures to support convection even with a cooler boundary layer
and showers and thunderstorms with locally heavy rainfall appear
likely. The GFS is faster than the European model (ecmwf) moving the system offshore
Wed night and Thursday, and our forecast rainfall chances will
linger into Thursday especially along the coast.
Friday looks like the driest day of the bunch as we may be in
between upper disturbances. Models are probably too warm with
temperatures Friday, especially inland, given what should again be
wet soil conditions after the Tuesday-Wednesday rainfall event.
By Saturday and Sunday, the East Coast trough will deepen
significantly as shortwaves dive into New England, the Great Lakes,
and perhaps the Midwest too. A rather strong cold front for the
middle of Summer is shown on both the GFS and European model (ecmwf) to approach the
Carolinas from the northwest on Sunday. This solution is overall
slower than yesterday's models showed. The European model (ecmwf) solution looks more
plausible given little GFS/Canadian ensemble support for the 12z
operational GFS cutting off shortwave energy to our west on Sunday.
Aviation /00z Monday through Friday/...
as of 00z...MVFR conditions from convection will occur across
all terminals for a brief time early this evening as the
current convection continues to weaken and slowly dissipate
across southeast NC and northeast SC. By 02z, any leftover
showers should dissipate by 03z. Will have to deal with
convective debris clouds for the remainder of this evening and
overnight. Models keep the debris bkn to ovc clouds in the mid
to upper levels ie. 5k to 15k ft later this evening and
overnight. Models keep boundary layer winds active all night
with winds at the sfc SW around 5 kt during the Mon pre-dawn
hrs. As a result, ground fog should not be an issue.
VFR conditions will dominate daylight Mon hrs with conditions
becoming ripe for atleast thunderstorms in the vicinity across the coastal terminals
during Mon daylight morning. This due to a mid-level S/W trof
passing in close proximity as it tracks over the adjacent atl
waters and off to the NE. Conditions across all terminals become
favorable for convection during Mon aftn and early evening with
occasional MVFR and IFR conditions possible.
Extended outlook...brief to occasional MVFR/IFR conditions from
showers and thunderstorms Mon night thru Wed becoming isolated
near term /through Monday/...
as of 230 PM Sunday...persistent southwesterly fetch between inland
trough and Bermuda high pressure will continue through the near term
period. As a result, southwesterly winds will prevail in the 15 to
20 knot range with steep wave conditions at 4 to 5 ft, especially
away from the coast (a little lower wave closer to the coast but
just as choppy). Convection possible across the waters tonight and
into Monday as the overall pattern begins to change. Will leave the
small craft should exercise caution as is spatially but carry it
Short term /Monday night through Tuesday night/...
as of 300 PM Sunday...a cold front will drop south and east
producing a tightened gradient flow as Bermuda high continues
remain to our east. The trough inland will also get pushed east
aiding to increased flow into Mon eve. Overall expect gusty SW
winds up to 20 kts or so into Mon night. This will maintain seas
up between 3 and 5 ft most waters.
As the cold front drops south by tues morning, the winds will
diminish to less than 10 kts closer to the coast, but may remain
up closer to 15 kts in the outer waters. The front will most
likely remain just west of waters through tues, especially as
sea breeze helps to kick it inland a bit. The boundary may be
bisecting the area by tues night into Wed and this could produce
lighter and more variable winds heading into Wed morning. Seas
should drop to 2 to 4 ft through tues morning and down to 3 ft
or less heading into Wed morning. You can also expect increased
thunderstorm activity with front in the vicinity which can
produce gusty and variable winds and lower visibility.
Long term /Wednesday through Friday/...
as of 300 PM Sunday...a stalled front over South Carolina should
provide the trigger for numerous showers and thunderstorms on
Wednesday. Winds mainly from the east should remain 10 knots or less
outside of storms. Weak low pressure developing along the front
should move offshore on Thursday and then well out to sea by Friday.
This should allow winds to veer southwesterly. Wind speeds should
increase to a solid 15 knots Friday as low pressure develops to our
north along a stronger cold front that might reach the Carolinas
early next week.
NC...high rip current risk until 9 PM EDT this evening for ncz110.
Coastal flood advisory until midnight EDT tonight for ncz107.