060
FXUS62 KRAH 050834
AFDRAH

Area Forecast Discussion
National Weather Service Raleigh NC
433 AM EDT Fri Jul 5 2024

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

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 430 AM Friday...

...Dangerously hot, with record temperatures and scattered afternoon-
evening showers/storms...

The Heat Advisory has been upgraded to an Excessive Heat Warning for
the ne Piedmont, nrn Coastal Plain, and the nrn Sandhills, where
heat index values around 110 F will be likely this afternoon. The
Heat Advisory remains otherwise unchanged in time and location, for
peak heat index values generally in the 105 to 109 F range.

A subtropical ridge will migrate slowly ewd and across the South
Atlantic states through 12Z Sat, while a shortwave trough and
accompanying compact, mid-level cyclone now over the upr MS Valley
will lift newd across the upr Great Lakes and into srn ON. Wly,
quasi-zonal mid-level flow of recent days over the srn Middle
Atlantic will back to swly. Within that swly flow regime, a well-
developed MCV from an ongoing MCS over sern MO and nrn AR will move
newd across the OH Valley today and across the cntl Appalachians and
nrn Middle Atlantic tonight. A trailing mid-level trough may glance
nrn and wrn VA and nwrn NC this evening.

At the surface, hot sswly flow will persist across the Carolinas and
srn Middle Atlantic, downstream of a convectively-reinforced cold
front that will extend from a ~1010 mb low over ern PA/MD and NJ
swwd into the srn Appalachians and TN Valley by 12Z Sat. An
Appalachian-lee trough will slightly precede the front and extend
across the Foothills and Piedmont of the srn Middle
Atlantic/Carolinas. The trough may be reinforced by a wind shift and
convergence axis left behind by outflow from Thu evening`s
convection, which was apparent in 08Z surface observational data
along an arc from DAN-HBI-CLT. The parent outflow boundary has lost
character at the surface (no longer discernible as a wind shift or
with any apparent cooling) but has continued sewd as an undular bore
and extended along an arc from near EWN-EYF-LBT. That feature will
likely exit Sampson Co. and reach sern NC and nern SC by 12Z this
morning.

850 mb temperatures that were observed at 21 C at GSO last evening
are forecast to increase another degree or two C and reach near 3
sigma above average over the Carolinas, beneath the subtropical, mid-
level ridge axis today. The corresponding area of 1440-1450 meter
1000-850 mb thicknesses that were observed in a small area over the
wrn Piedmont and at GSO last evening is forecast to expand in
coverage throughout cntl NC today. As such, already hot temperatures
of Thu will likely tick higher today, with widespread upr 90s to lwr
100s likely. Additionally, the upr 60s surface dewpoints that were
common Thu afternoon are likely to be replaced by lwr 70s dewpoints
this afternoon, except for a small area of upr 60s likely to
reappear with afternoon mixing over the srn Piedmont and wrn
Sandhills. The combination of hotter temperatures and higher surface
dewpoints on average will favor widespread heat index values of 105
to 109, with 110-112 F likely in the counties included in the
Excessive Heat Warning.

That increased heat and humidity will quickly erode morning
convective inhibition, amid ~5.5 to 6 C/km mid-level lapse rates
already in place per 00Z regional RAOB data. Widely scattered
showers and storms will likely develop by midday-early afternoon
along the surface features noted above, which may yield strong to
isolated damaging wind gusts while also locally/briefly cooling
localized areas. Somewhat greater concentration/multi-cell
clustering will be possible into the nw Piedmont this evening, where
upstream cells over nwrn NC may be focused by the glancing mid-level
trough and subsequently propagate into those areas.

It will otherwise remain very mild and muggy tonight, with lows in
the mid to upr 70s, to around 80 F in urban areas.

&&

.SHORT TERM /SATURDAY AND SATURDAY NIGHT/...
As of 330 AM Friday...

* Hot and humid conditions continue Saturday with heat indices
  climbing to 100 to 105 degrees
* Isolated to scattered flash flooding possible as storms will be
  slow moving and efficient rainfall producers.

A compact, but flattening, shortwave embedded within the broad
troughing will lift through the Lower Great Lakes into southern
Quebec by Sun morning. The related surface pattern will shift a
surface low into the Northeast with a trailing cold front extending
into the Ohio and Tennessee Valley. Weakening dynamics at the
surface will likely prevent the surface cold front from traversing
the Appalachian mountains. Ahead of the front and east of the
mountains, a continued hot and humid airmass will be in place as
early afternoon temperatures quickly rise into the 90s to around 100
degrees with surface dew points in the upper 60s to mid 70s,
resulting in heat indices of 100 to 105 degrees. Heat indices over
the western Piedmont may be closer to the mid 90s as
increasing/thickening cloud cover spreads in from the west and
proximity to greater chances for showers/storms and convective
outflow slowing rise in afternoon temps. Although details will be
dependent on convective activity Fri/Fri night, another heat
advisory will likely be needed for at least the Coastal Plain and
eastern Sandhills for Sat.

Showers and thunderstorms are expected to initiate along a lee
trough that develops with diurnal heating over the western Piedmont
with the a hot and humid airmass in place along and east of the
trough. Moderate instability is expected to develop by early
afternoon as MLCAPE values rise to 1500-2500 J/kg and MLCIN erodes.
Flooding will likely be the primary hazard with these storms with
anomalous deep layer moisture (PWAT >2.25), warm cloud layer between
10,000 to 15,000 and weak cloud layer flow and Corfidi vectors.
Additionally, deterministic Hi-Res guidance depicts initial storm
outflow to congeal creating basically an effective front draped SW
to NE across central NC that slowly progresses eastward with time.
This orientation would align cloud-layer flow parallel to the front
which would bring a risk for training storms. 00z HREF aligns with
theses thoughts depicting of 1" to 2"/hr rain rates and the
strongest storms capable of over 3"/hr. Current forecast has
widespread rain of 0.5 to 1.5 inches, but as finer details become
clear expect the range between min/mix to increase with isolated
locations capable of seeing over 3 inches.

&&

.LONG TERM /SUNDAY THROUGH THURSDAY/...
As of 330 AM Friday...

A rather persistent pattern is expected through the remainder of
the extended as central NC will be tucked 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. 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.

This pattern will favor continued above normal temperatures with
highs in the mid 90s in the urban areas and overnight lows only
reaching into the mid 70s. With continued heat related stresses heat
related illnesses will be possible especially among individuals
sensitive to heat and do not have access to effective cooling and/or
adequate hydration. Diurnally favored showers/storms and storms will
also be possible each afternoon into the evening, likely focused
along the lee-trough and any subsequent outflow boundaries
thereafter. Organized convection appears to be at a minimum with
deep layer shear remains weak around 10 to 20 kts, strongest across
the NW Piedmont, and result in mostly pulse summer-time
showers/storms. Greatest coverage could be Tues into Tues night with
proximity of mid/upper troughing swings through the Great Lakes
region.

&&

.AVIATION /08Z FRIDAY THROUGH TUESDAY/...
As of 215 AM Thursday...

IFR-MVFR visibility restrictions are expected at INT/GSO this
morning, amid mainly clear and calm and where around a half an inch
of rain cooled the air and wet the ground Thu evening. VFR
conditions are otherwise expected until scattered showers/storms
redevelop with afternoon heating. A slightly better chance (than
recent mornings) of stratus and fog will exist late tonight-Sat
morning, as low-level moisture and humidity values gradually
increase.

Outlook: A good chance of morning stratus and fog and mainly
afternoon-evening showers/storms will exist through early-mid next
week, as a surface trough/front settle into the region and interact
with an unseasonably moist air mass in place.

&&

.CLIMATE...
Record High Temperatures:

July 5:
KGSO: 98/2012
KRDU: 102/1999
KFAY: 101/2002

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

Record High Minimum Temperatures:

July 5:
KGSO: 74/1999
KRDU: 78/1902
KFAY: 77/2005

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

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

&&

.RAH WATCHES/WARNINGS/ADVISORIES...
Heat Advisory from 11 AM this morning to 8 PM EDT this evening
for NCZ007-021>023-038-039-073>075-078-083>086-088-089.
Excessive Heat Warning from 11 AM this morning to 8 PM EDT
this evening for NCZ008>011-024>028-040>043-076-077.

&&

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