-- Discussion containing changed information from previous version are highlighted. --
223
FXUS62 KRAH 270623
AFDRAH

Area Forecast Discussion
National Weather Service Raleigh NC
223 AM EDT Thu Jun 27 2024

.SYNOPSIS...
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A mid-level disturbance and surface cold front will move across NC
today. The front will linger across the southern and eastern
Carolinas through early Friday, before lifting back north as a warm
front. A stronger cold front will approach the area on Sunday.
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&&

.NEAR TERM /UNTIL 6 AM THURSDAY MORNING/...
As of 1025 PM Wednesday...

The latest surface analysis shows a cold front extending from
southern PA southwest across WV into KY with widespread
convection across northern and central VA ahead of the front. A
surface trough extends southwest from central VA through the
Triangle area to near Charlotte separating a moist and rich
airmass across the eastern Piedmont and Coastal Plain with dew
points in the lower 70s with dew points in the upper 60s to the
west. In addition, a combination/merger of the sea breeze and
outflow from convection across northeast SC is moving north
across the Triangle toward the VA state line. It remains a very
warm evening with temperatures in the lower to mid 80s in many
locations as of 10 pm.

A couple of isolated showers/storms have developed over the past
hour or two, one exited the Yadkin Valley heading into the Triad and
another northwest of Roanoke Rapids. Wouldn`t be surprised to see
some additional isolated showers/storms develop across central NC
into the overnight hours with lingering weak to moderate instability
persisting overnight as a shearing mid-level trough approaches
the region. In addition, more widespread convection in VA will
propagate south and wouldn`t be surprised to see outflow and the
approaching mid level trough maintain or initiate convection
that spreads south into the Piedmont near the VA border and the
northern Coastal Plain overnight. The best chance of convection
will be near the VA border and the northern Coastal Plain with
some dissipating precipitation possibly making it into the
Triangle and Rocky Mount areas late tonight. The low and mid-
level flow was quite weak per the 00Z GSO RAOB with 0-6km shear
less than 10 kts, while the flow will strengthen a bit
overnight, expect the severe weather threat to be confined to
the north in VA. It`s worth noting that DCAPE values remain
quite high and modest storms this afternoon over performed with
gusts of 30-40kts. Lows tonight will be quite mild and range
from the lower 70s near the VA border and Triad to the mid 70s
elsewhere which is about 7 to 10 degrees above normal. -Blaes

&&

.SHORT TERM /6 AM THURSDAY THROUGH 6 AM FRIDAY/...
As of 315 PM Wednesday...

A Heat Advisory has been issued for portions of central NC Thu, with
heat indices between 102 and 108 over portions of the Triangle,
Sandhills, and Coastal Plain.

A frontal boundary will likely be draped northeast to southwest from
the Mid-Atlantic into eastern TN to far western NC early Thu. The
front will try to move south and east through the day and evening as
high pressure settles into the northern Mid-Atlantic in western NY.
However, the front will most likely get hung up along the NC/VA
border sometime early Fri.

Some of the high-res models are indicating a secondary boundary
draping southward with convection from Wed night to early Thu
morning along US-64. Perhaps this is related to the lingering
discontinuity currently over southern VA. However, other guidance
indicates less of a defined wind shift. How this evolves may
ultimately depend on what happens with convection tonight across
northern NC and southern VA. With the uncertainty, we believe that
with warm overnight lows tonight in the mid 70s, high dewpoints in
the 70s again Thu, and max temperatures over the Triangle,
Sandhills, and Coastal Plain in the mid to upper 90s, will lead to
another heat risk across the region. Heat indices could be as high
as 108 over the far eastern Sandhills and southern Coastal Plain.
The only fly in the ointment is whether convection/clouds start
earlier in the day to limit daytime heating. For now, though, we
hedged toward enough solar heating for the higher heat risk. Highs
will be lower in the northwest Piedmont with upper 80s to near 90.

As for convection, some CAMs are showing the greatest coverage south
and east of the Triangle along their effective boundary, while
others extend convection further west to mainly along/east of US-1.
We hedged with this further west solution, thinking that any
boundary would be draped along US-64. Machine-learning models and
guidance suggest the prime storm risk would be between 1 pm and 8
pm, with greatest coverage along/east of US-1, with storms waning by
late evening and overnight as a mid-level trough axis slides south
of the region. SPC has continued a marginal risk of severe storms
mainly over the Sandhills to Coastal Plain. However, we would not be
surprised if that expands north and west to include the Triangle in
later updates. Point forecast soundings indicate high instability
upwards of 2000 J/kg, DCAPE around 1000 J/kg, and decent shear of 20-
30 kts from the WSW supportive of a damaging wind threat with any
stronger organized cells. Hail can also not be ruled out. As
convection wanes overnight, low stratus or fog may develop by early
Fri with lows in the upper 60s to mid 70s.

&&

.LONG TERM /FRIDAY THROUGH WEDNESDAY/...
As of 310 PM Wednesday...

This above-normal temp stretch will hit yet another crescendo this
weekend, with convection chances peaking late in the weekend. A
brief temp respite arrives early next week, however this will
quickly give way to a return to excessive heat midweek.

Fri/Fri night: The weak surface front is likely to settle across our
S areas Fri morning, then quickly wash out as the surface high to
our N shifts offshore by afternoon, resulting in a trend to light
low level flow out of the SE as warm mid level ridging spreads into
the Carolinas from the W. PW will be lower across the N but remain
close to 2" across the S, where weak low level confluent flow may
help organize scattered afternoon convection. Will carry chance pops
across the SE, where an inland-moving sea breeze could help focus
scattered convection, with a secondary chance over our NW given the
potential for terrain convection to drift into the Triad region.
Overall, though, coverage will be low as PW will be at or below
climo. Expect little or nothing across the NE, within the exiting
surface ridge, where LREF probabilities of substantial SBCAPE are
low. Highs should be in the upper 80s to the mid 90s. Heat index
values are projected to be 100-103 from the Triangle to the SE.

Sat-Sun night: Low level thermal ridging builds back into central NC
over the weekend from the SW, as a flat mid level ridge extends E
from the S Plains into NC through early Sun, our thicknesses rising
to 10-15 m above normal with deep mixing and weak lee surface
troughing over the Piedmont. Pops Sat will be similar to Fri, low
chances focused across the SE and NW. This ridge aloft then
retrogrades by late Sun as a potent northern stream trough moves
from the Upper Midwest/N Great Lakes through S Que/St Lawrence
Valley and into the interior Northeast by Sun/Sun night, digging
down the Mid Atlantic coast. Deep layer shear will be marginal Sun,
but moderate SBCAPE is expected, and the increasing and deepening
moisture (projected PWs nearly 2.5") with the approaching surface
front tied to the trough aloft will support higher pops in the good
chance to likely range, highest across the NW Sun afternoon through
the evening before shifting to the S and E as the front pushes to
our SE overnight. Expect highs from the low 90s NW to upper 90s SE
with high dewpoints well into the 70s, indicative of increased heat
stress as heat index values reach 100-110 over all but the extreme
NW both days (but likely a bit higher Sun than Sat), although
confidence in reaching extreme heat levels is lower Sun given the
potential for clouds and convection.

Mon-Wed: As the front settles along our S and E early next week,
pops should be on the low side, chance pops mainly S Mon and even
lower Tue, as surface high pressure builds in from the N within mid
level troughing. Low level thicknesses suggest highs fairly close to
normal, with highs in the upper 80s to lower 90s. The heat will
begin to return Wed as the surface high pressure exits and strong
mid level ridging builds once again, centered over the Mid South and
N Gulf states, sending thicknesses soaring back above normal once
again. After highs in the upper 80s to lower 90s Mon/Tue, highs
should again be in the low-upper 90s Wed. -GIH

&&

.AVIATION /06Z THURSDAY THROUGH MONDAY/...
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As of 215 AM Thursday...

An outflow boundary from previous and ongoing convection over VA
will continue to trigger additional showers/storms, and also cause
initially swly surface winds to become calm/variable or light nwly,
as it moves sewd at 10-15 kts across the nrn Piedmont and nrn
Coastal Plain of NC this morning. While patches of IFR-MVFR stratus
may develop in the rain-cooled air behind the boundary over the nrn
Piedmont, a higher probability of IFR-MVFR ceilings will exist at
FAY, as a separate area of 800-1900 ft AGL ceilings now developing
across nrn SC and srn NC --in a similar manner as Wed morning--
spread nwd to FAY and possibly at RDU/RWI through 12Z. Associated
ceilings, should they indeed develop as described, should then lift
and scatter to VFR through ~14Z.

A mid-level trough, embedded disturbances, and multi-layered
mid/high-level ceilings will then move east and across cntl-ern NC
today. The airmass ahead of the trough and clouds may destabilize
sufficiently for the redeveloppmnent of scattered early-mid
afternoon storms particularly from FAY ewd to the coastal Carolinas.

Outlook: IFR-MVFR stratus will again be possible especially at FAY
Fri morning and area-wide Sat-Sun mornings, followed by a good
chance of mainly afternoon-evening showers/storms Sunday.
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&&

.CLIMATE...
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Record High Temperatures:

June 27:
KFAY: 102/1998

June 30:
KFAY: 102/2012

Record High Minimum Temperatures:

June 27:
KGSO: 76/1969
KRDU: 76/1952
KFAY: 77/1998

June 28:
KGSO: 76/1969
KRDU: 76/1952
KFAY: 78/1914

June 29:
KGSO: 74/2010
KRDU: 78/1914
KFAY: 76/1969

June 30:
KGSO: 74/1936
KRDU: 80/1936
KFAY: 79/1936

July 1:
KGSO: 77/1970
KRDU: 75/2012
KFAY: 76/1990
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&&

.RAH WATCHES/WARNINGS/ADVISORIES...
Heat Advisory from 11 AM to 5 PM EDT Thursday for NCZ041-042-
077-078-085-086-088-089.

&&

$$
SYNOPSIS...MWS/Blaes
NEAR TERM...Blaes
SHORT TERM...Kren
LONG TERM...Hartfield
AVIATION...MWS
CLIMATE...RAH