337
FXUS62 KMHX 071805
AFDMHX

Area Forecast Discussion
National Weather Service Newport/Morehead City NC
205 PM EDT Tue May 7 2024

.SYNOPSIS...
High pressure will continue to strengthen offshore while weak
troughing continues for the next few days, as warm moist
southerly flow leads to unsettled conditions. A strong frontal
system will move through Friday.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 1045 AM Tuesday...

A wavy frontal boundary stretches west to east from the Ohio
Valley to the Mid-Atlantic Coast this morning, with a moist and
modestly unstable airmass to the south. Within the broad warm
sector, a narrow area of weak WAA is ongoing across the
Carolinas. Elevated convection is ongoing within the above-
mentioned zone of WAA, mainly impacting far SE NC. To the west
of ENC, weak showers were noted near the Raleigh metro, but
these have been weakening as they push east.

WAA is forecast to weaken with time, and I expect the ongoing
convection across SE NC will continue to weaken through the
lunch hour. The weak WAA is occurring on the backside of a weak
mid-level shortwave that is currently moving through ENC. In the
wake of this wave, short-wave ridging is forecast to move over
the eastern Carolinas, which will lead to a period of modest
subsidence during the typical peak in the diurnal convective
window.

Meanwhile, a moist southwesterly flow is forecast to keep
dewpoints in the mid 60s to low 70s, while a westerly low-level
flow support highs topping out in the mid to upper 80s. Despite
weak mid-level lapse rates, heating of the moist boundary layer
should support the development of moderate instability (MLCAPE
of 1000-1500 j/kg) by this afternoon. Then, as the mid-level
wave moves east, there will be a modest increase in
northwesterly flow aloft, supporting deep layer shear of
25-35kt. At face value, this shear/instability combo is
supportive of severe weather. But...

The forecast challenge today revolves around forcing. The
magnitude of subsidence forecast isn`t expected to be strong,
but is still noteworthy. Meanwhile, there doesn`t appear to be
any real large- scale forcing for ascent, which leaves the
seabreeze as the primary catalyst for initiation.

In light of all of the above, I expect the coverage of
convection to be much lower than yesterday. It should be noted
that some guidance suggests we will stay dry through tonight.
With westerly flow enhancing convergence on the seabreeze, I
still expect at least a few storms to form in the 2-5pm
timeframe. If a storm can develop AND be sustained for any
length of time, the environment appears supportive of hail of
penny to half-dollar size, and wind gusts of 40-60 mph. The
tornado risk still appears very low due to relatively higher
LCLs and weak low-level shear.

Convection is expected to be primarily diurnally-driven, with a
weakening trend expected after sunset.

&&

.SHORT TERM /WEDNESDAY THROUGH WEDNESDAY NIGHT/...
As of 145 PM Tuesday...

Mid-upper level ridging will shift offshore on Wednesday,
allowing more of a zonal flow aloft to develop from the TN
Valley east through the Carolinas. Within this flow, an impulse,
or two, lifting out of the Lower MS Valley will traverse the
Appalachians and Carolinas later Wednesday through Wednesday
night, interacting with a moist and unstable airmass to support
an increased risk of clusters of thunderstorms in a broad zone
from the TN Valley to the Carolinas. Locally, there will also be
some potential for convection along the seabreeze (which will
tend to be pinned closer to the coast thanks to the westerly
low-level flow forecast).

This type of setup is a classic one for MCS development, and I
expect a MCS, or two, to impact portions of the Carolinas
Wednesday/Wednesday night. This type of pattern can also be a
low confidence one, though, as models can sometimes struggle
with the evolution of convection as it moves downstream. This is
a pattern, though, that can support a longer-lived MCS running
the length of NC. And, locally, there is also the potential for
seabreeze convection unrelated to any MCS`, especially with less
ridging/subsidence compared to today. With all of the above in
mind, I have opted to go with a broad-brushed 30-40% chance of
thunderstorms for the entire Wednesday/Wednesday night period.
We`ll continue to refine when/where the best chance will be in
the coming shifts.

From a hazards standpoint, any MCS that develops will carry a
risk of damaging winds. Mid-level lapse rates are forecast to be
steeper than today (as high as 6.5-7.0 C/km), so hail will be a
concern both with linear segments and with any discrete storms
that manage to develop on the seabreeze. It`s also worth
pointing out that forecast MLCAPE of 2000-3000j/kg and deep
layer shear of 25-30kt will be supportive of instances of
higher-end severe weather for this area (ie. 60+ mph winds and
>1" size hail). The caveat is that the evolution of upstream
convection will have a significant impact on our airmass, as any
early convection would tend to keep instability lower, and
vice-versa. SPC has recently upgraded a portion of our area to a
"Slight" risk of severe weather, which appears warranted given
all of the factors outlined above.

&&

.LONG TERM /THURSDAY THROUGH MONDAY/...
As 330 AM Mon...There have been a few changes in the forecast
since the previous update but the overall trend remains the same
as ENC will remain unsettled into this weekend with a daily
chance for showers and thunderstorms into Friday before
potentially drying out on Sat. Highest risk for severe weather
still looks to be on Thursday. High pressure ridging finally
overspreads ENC early next week.

Thursday...Have made some tweaks to the forecast for Thurs
with the latest data and trends in mind. Upper level zonal flow
begins to overspread ENC on Wed out ahead of a positively tilted
upper trough which will be located in the Upper Midwest to
start the period. Within this zonal flow, guidance has come into
better agreement that a weak mid level disturbance will trek
across the Carolinas and then offshore Wed evening into Thurs
morning.

As Wednesday`s shortwave pushes off the coast, any leftover
shower and thunderstorm activity will quickly weaken Wed night
into Thurs and push offshore. As we get into Thurs, upper level
trough migrates over to the Great Lakes region while a jet
streak begins to expand over the Mid-Atlantic increasing lift.
At the mid levels a second and stronger mid level shortwave
rounds the base of the trough and tracks over the Mid-Atlantic
Thurs afternoon/evening while at the surface deepening low
pressure system in the Great Lakes tracks NE`wards into the
Northeast with its associated cold front nearing western NC and
a prefrontal trough setting up over the Coastal Plain Thurs
evening. With ample MLCAPE 1000-2000 J/kg over ENC in the
afternoon, stronger wind shear 30-40 kts, and slightly stronger
forcing, ENC will once again have another threat for scattered
showers and isolated to widely scattered strong to severe tstms.
Once again the main hazard within the strongest storms will be
damaging winds and hail. Given the higher risk for severe wx on
Thurs ENC is in a slight risk (level 2 out of 5) for severe
weather Thurs afternoon and evening. Highs each day get into the
low 90s inland and 80s across the OBX while lows only get down
into the 60s.

Friday through early next week... Upper level troughing finally
pivots out of the Great Lakes and overspread the Mid-Atlantic
on Fri into Sat with the last and likely strongest mid level
shortwave rounding this troughs base on Fri. This is where the
biggest change in the forecast has been as at the surface, low
pressure in the Northeast will continue to trek NE`wards while
its associated cold front finally tracks across the region
slowing as it pushes offshore. A wave of low pressure develops
along this frontal boundary on Fri as well and tracks along or
near the coast. The eventual track will have a major impact on
whether the area sees thunder on Fri as a low track just
offshore keeps us on the cool and more stable side while a low
track just inland gives us a threat for additional
thunderstorms on Fri. For now kept thunder in the grids for Fri
afternoon and evening until we get more clarity on the eventual
evolution of the forecast. Either way Friday looks to have the
best shot at widespread precip. Through the weekend and into
next week general troughing remains over the Eastern Seaboard
before gradually ejecting out into the Canadian Maritimes. Will
have one more chance at a frontal passage Sun evening into Mon
before surface ridging begins to overspread ENC from the west.
Temps do cool over the weekend closer to normal.

&&

.AVIATION /18Z TUESDAY THROUGH SUNDAY/...
SHORT TERM /through 18z Wednesday/...
As of 145 PM Tuesday...

KEY MESSAGES

- Lower TSRA risk today compared to yesterday

- Increased TSRA risk on Wednesday

FORECAST DETAILS

A few SHRA have recently developed across northern sections of
Eastern NC, but the coverage has been much lower compared to
yesterday. I expect this to continue to be the case, with the
best chance of a SHRA or TSRA being confined closer to the close
where the seabreeze will offer the best lift. Otherwise,
quieter conditions expected through tonight for aviation
interests. On Wednesday, the risk of TSRA is forecast to
increase once again, however the latest guidance suggests this
risk will be focused after the current 18z TAF cycle. Given
radar trends this afternoon, I opted to remove VCTS from the
TAFs given lowering confidence. I have also kept TS out of the
TAFs for Wednesday, as the better chance appears to be later in
the day.

LONG TERM /Wednesday night through Sunday/...
As of 330 AM Tue... Expecting primarily VFR conditions outside
of any shower and tstm activity Wed night and Thurs with the
best shot at seeing widespread sub-VFR conditions on Fri. VFR
conditions then return on Sat across the CWA.

&&

.MARINE...
SHORT TERM /through tonight/...
As of 7 AM Tue...Latest obs show SW winds 10-20 kt with seas
2-4 ft. SW/WSW winds 10-20 kt expected for most of today with
seas 3-5 ft. Expect another surge 15-25 kt late this afternoon
and into tonight with strengthening thermal gradient. Given how
winds overachieved a bit Monday evening, went ahead with a SCA
for the central and southern waters late this afternoon into
tonight, with potential for a period of frequent gusts to 25 kt
along with seas building to 4-6 ft. May need to be extended into
the Pamlico Sound as well. Sct showers and tstms expected
across the waters today.

LONG TERM /Wednesday through Saturday/...
As of 340 AM Mon... Not much change in the forecast overall as
unsettled weather will remain in place into the end of the week
promoting a daily chance at showers and thunderstorms across
our waters each day. Locally enhanced winds and seas will be
possible within any thunderstorm that makes its way into the
area. Otherwise the background winds remain SW`rly at 10-20 kts
on Wed with a few gusts up near 25 kts at times Wed aftn and
evening as the thermal gradient sets up. As we get into
Thursday, gradient tightens out ahead of an approaching cold
front allowing winds to increase closer to 15-25 kts with gusts
in excess of 20-30 kts across our waters. Strongest winds will
be located across our coastal waters and larger sounds likely
necessitating a SCA for Thurs across portions of ENC. As the
front nears and begins to push offshore on Fri winds decrease
closer to 10-15 kts and become more W`rly on Fri before
becoming NW`rly and increasing slightly to 15-20 kts Fri night
behind the frontal passage. NW`rly winds continue through Sat
before winds return to a S`rly direction towards the end of the
weekend. 3-5 ft seas along our coastal waters on Wed increase to
4-7 ft on Thurs as the winds increase with some 8 ft seas
possible along the Gulf Stream waters. Seas gradually ease over
the weekend as winds ease down to 2-4 ft.

&&

.MHX WATCHES/WARNINGS/ADVISORIES...
NC...None.
MARINE...Small Craft Advisory until 5 AM EDT Wednesday for AMZ152-154-
     156-158.

&&

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