Area Forecast Discussion
Issued by NWS Wilmington, NC

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FXUS62 KILM 240711
AFDILM

Area Forecast Discussion
National Weather Service Wilmington NC
311 AM EDT Mon Jul 24 2017

.SYNOPSIS...
Heavy rain in bouts of showers and thunderstorms, sometimes
numerous, will raise the risk for excessive rainfall and
possible flooding through mid week. A cold front will approach
from the north and should slip into the area later Tuesday night
and on Wednesday before stalling and then dissipating by
Thursday. The arrival of a stronger cold front this weekend
will bring numerous thunderstorms back into the eastern
Carolinas.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 300 AM Monday...Pattern aloft continues to transition to
broad troughing over the eastern CONUS while at the surface
Bermuda High sits off the coast. Convection today is likely to
be similar in nature to yesterday. Some development along the
sea breeze with additional storms developing along the Piedmont
trough. Guidance is showing a weak shortwave dropping southeast
in the northwest flow aloft. Water vapor imagery shows this
feature nicely, currently moving across IN/OH and into KY.
Arrival time for the wave based on its movement would be early
to mid afternoon. PVA ahead of the wave combined with diurnal
heating and increasing instability due to mid level cooling
should produce another round of afternoon showers and
thunderstorms, although initiation may start a little earlier.
As is the case this time of year, severe weather is possible
although widespread severe is not expected. Shortwave and the 5h
trough help push a cold front into the Carolinas just as the
period is ending. Precipitable water values remain over 2 inches
today and any deeper convection will have the potential to
produce a lot of rain in a short amount of time.

Temperatures above climo will continue away from the coast but
continued mid level cooling and increased cloud cover will keep
highs a little cooler than yesterday. Highs will range from mid 90s
inland to upper 80s and lower 90s along the coast. Debris cloud will
linger over the area once again tonight and combined with continued
south to southwest flow will keep lows well above climo, mid to
upper 70s.

&&

.SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/...
As of 300 AM Monday...We are expecting an active period and
this will result in heavy rainfall across the area. We are
currently expecting 2 to 3 inches of additional rainfall on
average across the Forecast Area during this period.

A deepening trough is expected to evolve across the east coast
and this will keep the weather unsettled across the eastern
Carolinas with bouts of showers and thunderstorms, sometimes
numerous. The mid and upper trough may actually close off for a
time Tue night and Wed. The trough may drift offshore by the end
of the period, but will remain in close proximity even on Thu.
At the surface, the Piedmont Trough will be displaced eastward
on Tue with a cold front drifting south and into the Forecast
Area late Tue night and Wed. Weak surface low pressure,
coincident with mid/upper level low, will help to stall the
front overhead or in close proximity Wed/Wed night.

NAM BUFR soundings actually show brief drying in the mid levels
on TUE before the moisture reloads Tue night into Wed. The
soundings from the GFS do not show this drying and maintain
precipitable water values at or jut above 2 inches throughout.
It would be a mistake at this point to hone in on the finer
timing details of the differing model solutions. It is enough
to say that with a front lingering in the area and given the
upper level support expected, the prospects for unsettled
weather is high as is the risk for excessive rainfall. Storm
motions are expected to be less than 10 kt which of course
increases the risk for significant flooding. At least localized
flooding should be expected with urbanized areas and areas that
drain poorly the most susceptible.

The environment is not particularly supportive of severe
weather as wind fields will be light. Instability will be rather
marginal given the time of year as abundant cloud cover helps
to hold down temps. Downdraft CAPE values would however suggest
that thunderstorms that are able to gain sufficient height may
generate a brief damaging downburst of wind.

Highs on Tue will be in the upper 80s to near 90 with mid 80s on
Wed. Lows will be in the lower to mid 70s.

&&

.LONG TERM /THURSDAY 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
thus far this year include 95 in Lumberton and 96 in Florence.
Both sites typically have hit 100 by this late in the summer.

The GFS is faster than the ECMWF in moving potent upper
disturbance offshore 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 all the heavy rainfall.

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 ECMWF to
approach the Carolinas from the northwest on Sunday. This
solution is overall slower than yesterday`s models showed. The
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 /06Z MONDAY THROUGH FRIDAY/...
As of 06Z...Convective debris clouds linger over the area this
morning with patches of marine stratus occasionally moving
onshore. Gusty southerly winds along the coast are helping push
MVFR and IFR stratus into the coastal terminals. Think IFR will
be shorter duration and for now have kept MVFR as the dominant
category.

Expect VFR conditions today with another round of afternoon and
evening showers and thunderstorms. Coverage will be similar to
yesterday with inland sites having slightly better chances for
afternoon storms but all terminals will have potential for brief
periods of MVFR and IFR conditions with any storm. Loss of
heating will once again bring a decrease in storm coverage and
intensity. However, debris clouds left over from storms will
linger through the end of the period, mainly as mid level cloud
around 12k ft.

Extended Outlook...Brief to occasional MVFR/IFR conditions from
showers and thunderstorms Mon night thru Wed becoming isolated
on Thu.

&&

.MARINE...
NEAR TERM /THROUGH TONIGHT/...
As of 300 AM Monday...Strong south to southwest flow continues today
with winds in excess of 20 kt at times. Winds have pushed seas over
6 ft in some areas and will keep seas over 6 ft into the afternoon
before gradient weakens later in the day and both winds and seas
subside. No changes planned to the inherited headlines, will
maintain SCA from Surf City, NC to Murrells Inlet, SC and SCEC along
the Georgetown County coast. Bermuda High will remain in place
tonight with southwest flow dropping from a solid 20 kt around
midday to 15 kt around midnight and near 10 kt by the end of the
period. Seas will fall from 4 to 6 ft today to 3 to 5 ft this
evening and down to 2 to 4 ft late in the period.

SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/...
As of 300 AM Monday...A front to our N will make inroads into
our waters late Tue night and on Wed before stalling out Wed and
Wed night. Wind speeds on Tue will be 10 to 15 kt with the
direction ahead of the Piedmont Trough holding from the SW. Wind
speeds for the remainder of the period will be 10 kt or less
and actually winds will become light and variable in direction
with a cold front lying across the area late Tue night and Wed
morning. The direction should settle on E or ESE during Wed and
Wed night, but wind speeds will remain 10 kt or less. Seas will
be mainly 3 ft Tue and Tue night and 2 ft Wed and Wed night.
Numerous to widespread thunderstorms through the forecast period
will not only create poor visibility in heavy rain, but will
produce locally higher winds and seas.

LONG TERM /THURSDAY THROUGH FRIDAY/...
As of 300 PM Sunday...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 back to
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.

&&

.ILM WATCHES/WARNINGS/ADVISORIES...
SC...None.
NC...None.
MARINE...Small Craft Advisory until 6 PM EDT this evening for AMZ250-
     252-254.

&&

$$

NEAR TERM...III
SHORT TERM...RJD
LONG TERM...TRA
AVIATION...III


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