539
FXUS62 KMHX 010723
AFDMHX

Area Forecast Discussion
National Weather Service Newport/Morehead City NC
323 AM EDT Wed May 1 2024

.SYNOPSIS...
A weak surface trough will move through the area today. High
pressure then builds in for a couple of days before yet another
cold front impacts the area over the weekend.

&&

.NEAR TERM /THROUGH EARLY EVENING/...
As of 200 AM Wednesday...

A weak upper level shortwave will move slowly east across the
Coastal Carolinas today. At the SFC, a weakening trough/cold
front will approach ENC from the NW through the day. Early this
morning, modest elevated moisture transport and weak large-scale
forcing with the shortwave will support scattered showers and
perhaps a few thunderstorms. Weak effective shear should keep
the risk of strong thunderstorms low, with the greatest
thunderstorm risk focused offshore.

By this afternoon, modest moisture advection ahead of the front
and upper level wave should allow dewpoints to rise into the
mid 60s. Heating of the moist boundary layer should support
moderate instability, on the order of ~1000 j/kg SBCAPE. Early
in the afternoon, deep layer shear is forecast to be weak
(~20kt). However, by mid to late afternoon, the flow aloft will
become northwesterly atop a southerly SFC wind. This will give a
little curvature to the hodograph, and will lead to a modest
increase in deep layer shear to around 25-30kt. At face value,
this type of environment is generally supportive of multicell
clusters capable of gusty winds of 30-50 mph. The severe weather
threat in an environment like this is low (<10% chance), but
isn`t zero. I suspect the "best" chance of seeing a marginally
severe thunderstorm would be during the mid to late- afternoon
period as the deep layer shear increases. Storm motions will
tend to be erratic today, focusing along outflow boundaries and
the seabreeze. The upper level steering flow will be changing
through the day as well, which may lead to a mean southeasterly
flow with time.

One caveat with the thunderstorm coverage and intensity today
is questionable forcing. Low-level convergence with the above-
mentioned cold front is forecast to weaken with time as it
approaches the coastal plain. Meanwhile, a seabreeze is expected
to develop, and this may end up being the best focus of low-
level convergence. Between the weakening front, the seabreeze,
and some weak support with the upper level shortwave, there
still appears to be a decent signal for scattered thunderstorms
focused in the 12pm-7pm timeframe. I didn`t stray too far from
the previous forecast regarding coverage today, but it should be
noted that the lack of stronger forcing shows up in some short-
term guidance with a lower coverage. I suspect the seabreeze
will be the primary driver of convection today, with the surface
front adding some support. The lack of stronger forcing should
also help to keep the severe weather risk at bay as this will
tend to lower the risk of deeper, more sustained, updrafts.

Where thunderstorms occur, rainfall amounts are forecast to
average in the 0.25-0.75" range. With an initially weak
steering flow, slow storm motions may support rainfall amounts
as high as 1-3" for some. Even where the highest rainfall
amounts occur, flooding is not expected to be a big impact,
primarily due to the lack of appreciable rainfall of late.

&&

.SHORT TERM /TONIGHT/...
As of 200 AM Wednesday...

Thunderstorm activity should be diurnally-driven, with a
downward trend in coverage and intensity after 7pm this
evening. In the wake of the thunderstorms, winds will be very
light, or even calm, and skies will attempt to clear out. This
plus whatever rain falls today should support an increased fog
potential tonight. There is some uncertainty with how much
clearing will occur, but the pattern, plus model guidance,
supports a risk of dense fog.

&&

.LONG TERM /THURSDAY THROUGH TUESDAY/...
As of 330 PM Tuesday...

KEY MESSAGES

- Inland highs in the low to mid 80s for the rest of the week

- Best rain chances Wednesday and then an unsettled weekend and
  start to the new week

FORECAST DETAILS

We return to warm, dry weather on Thursday and Friday with a
ridge building over the southeast US. Highs will be in the mid
80s across the coastal plain and low 70s at the beaches.

Unsettled weather returns this weekend with multiple chances for
showers and thunderstorms. Surface high pressure will be
gradually washed out as a surface low forms due to a shortwave
trough moving across the southeast. At the same time, a cold
front associated with a deep low over south-central Canada will
move into our area and stall. PoPs increase west to east on
Saturday with shower and thunderstorm activity possible through
Monday (15-30% chance).

&&

.AVIATION /07Z WEDNESDAY THROUGH SUNDAY/...
SHORT TERM /through 06z Thursday/...
As of 130 AM Wednesday...

KEY MESSAGES

- TSRA risk on Wednesday

- BR/FG likely late Wednesday evening (60-80% chance)

FORECAST DETAILS

A weak upper level wave, and an associated surface trough, will
move slowly east across the coastal Carolinas over the next 24
hrs. These features will combine with a moistening and
destabilizing environment, leading to an increased risk of SHRA
and TSRA. Overnight, the TSRA risk looks to be highest offshore
and perhaps as far inland as KMRH and KNJM. That is also the
area that stands the best chance of low VFR CIGs (3-5k ft) over
the next several hours. With continued low-level moistening,
there will be a window of opportunity for a period of MVFR CIGs
along and east of a line from OAJ to EWN. Guidance isn`t sold on
the lower CIGs, so for now I`ve opted to go with a SCT020 layer
to reflect the potential.

On Wednesday, afternoon heating plus the seabreeze and the
above- mentioned front and upper wave will likely lead to
scattered SHRA/TSRA, with a focus in the 17z-23z timeframe.
Where TSRA occur, sub-VFR conditions are likely (VIS and CIGs).
The strongest TSRA will be capable of gusty/erratic winds to
40kt+. At this time, though, the risk of 50kt+ winds looks low
(<5% chance at any one terminal). In the wake of the TSRA, light
winds, clearing skies, and recent rainfall should support an
increased risk of sub-VFR VIS due to BR/FG. The greatest BR/FG
impacts are expected to hold off until after the current TAF
cycle.

LONG TERM /Thursday through Sunday/...
As of 330 PM Tuesday...Pred VFR expected through the period but
a few instances of unsettled weather are expected. By Saturday,
a cold front will be moving into the area and bring another
chance for showers and thunderstorms (15-30%). Lowered CIGs and
VIS are expected during these times.

&&

.MARINE...
SHORT TERM /through tonight/...
As of 200 AM Wednesday...

A weak cold front will move slowly southeast across the ENC
waters late this afternoon through tonight. Because of the weak
nature of the front, I do not expect a significant northerly
wind surge to develop. In fact, a weakening gradient around the
front is expected to keep winds light (5-15kt) for most of the
day and into tonight. Seas of 3-4 ft are forecast to slowly lay
down through tonight. However, the ongoing long-period ENE swell
of 3-4 ft at 12-13s hasn`t been modeled as well, and seas may
not lay down as quick as forecast.

Scattered showers and thunderstorms will impact the central and
southern waters this morning, associated with an upper level
wave approaching from the west. During the afternoon hours, the
thunderstorm threat will shift inland with the seabreeze, mainly
impacting inland rivers and sounds. Some of those thunderstorms
may work back towards the coastal waters this evening, but
confidence in this is low. Once the thunderstorms dissipate,
there will be an increased risk of fog. The potential exists for
a period of sub 1SM visibilities during this time, and we`ll
monitor this in later forecasts in case a Marine Dense Fog
Advisory is needed.

LONG TERM /Thursday through Sunday/...
As of 330 PM Tuesday...

KEY MESSAGES

- Sub-SCA conditions with multiple chances for showers and
  thunderstorms

FORECAST DETAILS

Although marine conditions are forecast to remain below SCA
criteria, opportunities for showers and thunderstorms are
possible this weekend. Winds will be variable through the
period due to several systems moving through but will remain
around 5-10 kt with 2-4 ft seas.

&&

.MHX WATCHES/WARNINGS/ADVISORIES...
NC...None.
MARINE...None.

&&

$$
SYNOPSIS...MHX
NEAR TERM...RM
SHORT TERM...RM
LONG TERM...OJC
AVIATION...RM/OJC
MARINE...RM/OJC