712
FXUS62 KRAH 050744
AFDRAH

Area Forecast Discussion
National Weather Service Raleigh NC
344 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 330 AM Friday...

Portions of the northeast Piedmont, northern Coastal Plain, and
northern Sandhills in central North Carolina have been upgraded
to an Excessive Heat Warning today from 11 AM to 8 PM.
Dangerous heat indices of around 110 degrees are expected. A
heat advisory remains in effect for the remainder of central NC.
Updated discussion coming soon with more information.

Previous discussion as of 835 PM Thursday...

* Heat Advisory is in effect for Friday with dangerously hot
  conditions expected.
* Widespread heat index values of 105 to 109 are expected for
  several hours during the afternoon.
* Temperatures wont fall back into the lower 80s until around
  midnight.

The mid and upper level ridge across the Deep South will persist but
deamplify a bit on Friday as a broad trough and embedded closed low
move across the northern Plains. At the surface a lee tough will
extend south across the western Piedmont of VA and the Carolinas. A
cold front will advance slowly east into the eastern OH and TN
Valleys on Friday afternoon. The air mass across the Carolinas warms
additionally on Friday with morning low level thickness values
ranging in the 1420 to 1428m range along with 850 mb temperatures
that climb to between 20 and 24 C Friday afternoon. This air mass
should support highs in the mid 90s to around 100 with low 100s
expected in some of the typically hotter locations such as KRDU,
KFAY, and KMEB. Combining the hot temperatures with elevated dew
points will result in widespread heat index values of 105 to 109.

Scattered thunderstorms are apt to develop across western NC during
the afternoon and slowly push east into the western Piedmont late in
the afternoon and especially during the evening. Other more widely
scattered thunderstorms may develop across the northern Coastal
Plain. The airmass across central NC will be moderately to strongly
unstable with MLCAPE values ranging from 1500 to 2500 J/kg. Profiles
suggest a primary threat of damaging winds with steep low level
lapse rates and elevated DCAPE. The convection is apt to continue
into the evening before dissipating overnight. Outside of the
thunderstorm cooled areas, temperatures are likely to linger in the
upper 80s to lower 90s through at least mid evening and wont fall
into the lower 80s until around or a little after midnight. Low
temperatures should eventually fall into the mid to upper 70s by
daybreak Saturday. -Blaes

&&

.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...Blaes
SHORT TERM...Swiggett
LONG TERM...Swiggett
AVIATION...MWS
CLIMATE...RAH