330
FXUS62 KRAH 061149
AFDRAH

Area Forecast Discussion
National Weather Service Raleigh NC
749 AM EDT Sat Jul 6 2024

.SYNOPSIS...
A subtropical ridge will continue to extend across the South
Atlantic states ahead of a cold front that will move into the
southern Middle Atlantic and Carolinas this afternoon and evening,
then stall and dissipate over the region through the weekend.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 415 AM Saturday...

...Continued dangerously hot, with record temperatures and numerous
afternoon-evening showers/storms with locally heavy rain...

The Heat Advisory has been upgraded to an Excessive Heat Warning for
the Coastal Plain, the ern Sandhills, and a portion of the ne
Piedmont, where heat index values at or above 110 F are forecast
again this afternoon. The Heat Advisory has also been expanded to
include Anson, Stanly, Montgomery, Randolph, and Person Co.

A mid-level, subtropical ridge along the South Atlantic coast will
strengthen slightly and bulge nwd along the srn Middle Atlantic
coast today. In swly flow to the west of the ridge, a series of
convectively-amplified disturbances will track from the lwr MS
Valley newd and across the TN Valley, srn Appalachians, and srn
Middle Atlantic. The most influential of these disturbances for cntl
NC appear to be a couple now over cntl GA and e-cntl AL, remnant to
now-dissipated upstream convection there, which should track
generally newd across the Upstate of SC and srn Appalachians this
morning and across cntl NC this afternoon and evening.

At the surface, hot sswly flow will persist across the Carolinas and
srn Middle Atlantic, downstream of a lee trough that will become an
effective front as convection and outflow focus along it and edge
ewd into cntl NC later this afternoon and evening. The trough may be
initially reinforced by a wind shift and convergence axis left
behind by outflow from multiple rounds of convection over the nw
Piedmont in the past 12 hours, which was draped at 08Z from near HNZ
to EQY. The sea breeze will meanwhile retreat inland and may
ultimately merge with the trough/front over the Sandhills and ern
Piedmont by this evening.

The airmass in place over cntl and ern NC will remain relatively
unchanged from Fri until convection and outflow are introduced into
it today, first probably along the aforementioned outflow-reinforced
trough/front. That trough/front may also be strengthened by a zone
of differential heating along the ern edge of periods of mid-high
level clouds focused over the nw Piedmont, amid the swly flow aloft.
As such, temperatures today are again likely to reach the upr 90s to
around 100 F, with lwr-mid 70s surface dewpoints throughout the
Excessive Heat Warning, ranging to lwr-mid 90s and upr 60s to near
70 along and west of the surface trough/front (over the nw
Piedmont).

Like Fri, initially widely scattered convection will likely develop
with midday-early afternoon heating, with clustering and
concentration of slow-moving cells along the trough/front as it
edges ewd across cntl NC and is overspread by MCV forcing. High PWs
of 2-2.25" and slow-moving/backbuilding nature of cells may result
in isolated to scattered instances of flash flooding, despite
relatively high 3-hr flash flood guidance values of 3-5" outside of
urban areas. Mesoscale trends of the MCVs and eventual favored
location of the surface trough/front may necessitate issuance of a
shorter-fused Flash Flood Watch later this morning. While one was
considered for all of cntl NC with this forecast issuance, that
would probably be too broad given the mesoscale uncertainties.

Convection should generally diminish in coverage and intensity
through midnight, though areas of remnant, light stratiform rain
from mid-level ceilings may linger well into the morning. It will
otherwise remain very mild and muggy tonight, with lows centered in
the mid 70s.

&&

.SHORT TERM /SUNDAY THROUGH SUNDAY NIGHT/...
As of 410 AM Saturday...

A weak area of surface high pressure centered over the Ohio Valley
Sun morning will shift NE over the Lower Great Lakes and help push a
cold front across the northern Appalachians towards the NC/VA border
by early Sun afternoon. Farther to the south over Coastal Carolinas,
surface dew points will mix out into the upper 60s. In between these
two theta-e boundaries a hot and humid airmass will be in place
where temperatures in the upper 80s to low 90s along with dew points
in the low/mid 70s will support moderate instability of 1500 to 2500
J/kg. Convective temperatures will easily be achieved by early
afternoon with point soundings highlighting a moist thermodynamic
profile through the depth of the troposphere as PWAT values approach
or exceed 2.25 inches.

Storm organization will be limited with weak deep layer shear in
place (10-15 kts 0-6km shear) with central NC tucked in a weakness in
500mb flow. This will tend to favor more pulse thunderstorm
development and limiting severe potential, although isolated strong
to severe wet downbursts will certainly be possible with the
strongest updrafts. The bigger threat will be isolated flooding
potential mainly in urban and poor drainage locations given the slow
storm propagation capable of efficient rainfall production. Highs
will be slightly cooler Sun as 850mb temperatures drop 18-19C, which
will favor near to slightly above normal temperatures (88-93F)
warmest in the southeast. Overnight lows will again provide little
relief especially in urban areas from the heat bottoming out in the
mid 70s.

&&

.LONG TERM /MONDAY THROUGH FRIDAY/...
As of 410 AM Saturday...

A persistent synoptic pattern is expected through the remainder of
the extended as central NC will be positioned between broad
reinforcing troughing through the central CONUS with the stationary
sub-tropical high broadly draped across the western Atlantic in the
eastern GOM. NWP guidance has been consistent with a closed low
drifting across the western Atlantic and retrograding towards the
Carolina coast, but is expected to remain over the Atlantic before
completely dissipating through Tues night. At the surface, a diffuse
pressure gradient will feature a lee-trough redeveloping over the
region each afternoon with continued anomalous deep layer moisture
in place as PWAT values remain at-or-above 2 inches.

Precipitation chances will be diurnally driven with greatest
coverage each afternoon/evening along the lee trough, expected to
redevelop each afternoon, and along the inland retreating seabreeze.
Storm mode is expected to predominately pulse thunderstorms as deep
layer shear of 10-15 kts at best is expected. Isolated instances of
strong to severe wet downbursts will be possible while deep warm
cloud layer and slow storm motions will provide a non-zero chances
for isolated flooding. Temperatures through Thurs will waver near
climatology for early/mid June with highs ranging from upper 80s to
low/mid 90s and lows mainly in the low/mid 70s.

&&

.AVIATION /12Z SATURDAY THROUGH WEDNESDAY/...
As of 745 AM Saturday...

VFR conditions are forecast until and outside of scattered to
numerous, slow-moving showers/storms that are expected to redevelop
with daytime heating along a surface trough/front this afternoon,
then continue into this evening. A series of mid-level disturbances
will continue to track newd across the region and result in a
continued chance of showers and storms, and/or stratiform rain from
prior convection, throughout the night. Widespread rain-cooled
air/outflow and high near surface relative humidity values will also
favor the development of areas of IFR stratus late tonight-Sun
morning.

Outlook: A somewhat-typical summer time pattern of afternoon-evening
showers/storms and morning stratus and fog are expected through mid-
week.

&&

.CLIMATE...
Record High Temperatures:

July 6:
KRDU: 102/2022
KFAY: 99/1990

Record High Minimum Temperatures:

July 6:
KGSO: 76/1999
KRDU: 79/1900
KFAY: 76/2017

July 7:
KGSO: 73/2019
KRDU: 77/1900
KFAY: 78/2017

July 8:
KGSO: 76/2010
KRDU: 78/1986
KFAY: 79/2012

July 9:
KGSO: 76/1987
KRDU: 74/2014

&&

.RAH WATCHES/WARNINGS/ADVISORIES...
Heat Advisory from 11 AM this morning to 8 PM EDT this evening
for NCZ007>009-023>025-039-040-073>076-083-084.
Excessive Heat Warning from 11 AM this morning to 8 PM EDT
this evening for NCZ010-011-026>028-041>043-077-078-085-086-
088-089.

&&

$$
SYNOPSIS...MWS
NEAR TERM...MWS
SHORT TERM...Swiggett
LONG TERM...Swiggett
AVIATION...MWS
CLIMATE...RAH