804
FXUS62 KRAH 170100
AFDRAH

Area Forecast Discussion
National Weather Service Raleigh NC
900 PM EDT Tue Jul 16 2024

.SYNOPSIS...
A strong subtropical ridge will gradually weaken over the Southeast
though mid-week. A cold front will settle into the Carolinas on
Thursday, then become quasi-stationary while weakening into the
weekend.

&&


.NEAR TERM /THROUGH TONIGHT/...
As of 900 PM Tuesday...

A few showers and storms still developing across the region along
the boundary that is stretching from SW to NE. Precipitation is
mainly focused over the Sandhills region and then NE along the US1
corridor. As the boundary pushes through the region this evening,
energy along with loss of heating is expected to diminish.  A few
lingering showers are possible late overnight, but any showers are
expected to be light. Lows tonight across Central NC will be in the
mid/upper 70s.

As of 400 PM Tuesday...A positive tilt, convectively-amplified shear
axis in the mid-levels will persist from the lwr MS and TN Valleys
newd and across the srn Appalachians and Carolinas through 12Z Wed,
between a couple of subtropical highs centered over the srn Rockies
and the cntl through swrn N. Atlantic. Weak, and weakly perturbed,
wswly to swly mid-level flow will result across cntl NC. Within that
regime, a couple of small MCVs appear to have developed within
clusters of ongoing convection over nwrn NC and sern TN/nrn GA,
respectively. The first will move enewd across the NC Piedmont
through this evening, while the trailing one over sern TN will move
across the Upstate of SC and into the srn/wrn NC Piedmont by 12Z
Wed.

At the surface, and on the wrn periphery of high pressure centered
near and east of Bermuda, a couple of lee troughs have been apparent
in observational data from cntl SC/GA newd into the NC Sandhills and
over the far wrn Piedmont/Foothills of VA/NC, respectively. These
troughs will continue to focus weak convergence and development of
isolated-widely scattered convection this afternoon, with some
potential for multi-cell clustering and ewd propagation into at
least the nw Piedmont through early this evening, then probably in a
weakening state as it encounters a nocturnally stabilizing
environment from the Triangle sewd through ~01-02Z. While convection
should consequently dissipate prior to midnight, some early morning
redevelopment cannot be ruled out with the approach of the upstream
MCV into the srn/wrn NC Piedmont near, and more likely just after,
12Z Wed. It will otherwise be muggy and very mild and mostly in the
mid-upr 70s.

&&

.SHORT TERM /WEDNESDAY AND WEDNESDAY NIGHT/...
As of 315 PM Tuesday...

...A heat advisory has been issued for the Coastal Plain on
Wednesday from 12 PM to 7 PM...

Potentially the final day of the oppressive heat is expected on
Wed for central NC. Low-level thicknesses and 850mb
temperatures subtly cool with glancing influence from a broad
mid/upper trough as it pivots across southern Ontario through
the period. The result should be highs not-as-hot as previous
days, but still reaching into the mid/upper 90s by early
afternoon with forecast heat index values, in the absence of
storms, expected to rise above 105 once again in the Coastal
Plain. Westward extent of the Heat Advisory remains uncertain as
surface dew points mix out in the west and increased deep layer
moisture will result in increased cloud cover and earlier storm
initiation. The Heat Advisory was issued where greatest
confidence in dangerous heat will be possible before storm
initiation and may need to be expanded westward to include the
Triangle with subsequent updates.

Showers/storms are again expected to be in greater coverage compared
to previous days as better moisture and slightly perturbed mid-level
flow spreads into the area. The airmass by early afternoon will be
hot and humid with MLCAPE 1500 to 2500 J/kg and moderate DCAPE
around 1000 J/kg. Marginal storm organization will be possible as
the upper trough pivots eastward and 15 to 25 kts of perturbed mid-
level flow will leak east of the mountains and over the northern
portions of the forecast area. Pulse-like airmass storms will be
possible south of Raleigh with wet downbursts the most likely
hazard. From Raleigh northward, some storm clusters congealing along
common cold pool may result in isolated increased wind threat.

&&

.LONG TERM /THURSDAY THROUGH TUESDAY/...
As of 216 PM Tuesday...

* Widespread rainfall expected Thursday into Friday
* Unsettled weather continues this weekend into early next week
* Cooler temperatures from Friday through early next week

The forecast remains on track for widespread showers on Thursday as
a slow moving cold front arrives in central NC, stalls, and remains
in the vicinity through the weekend. The surface boundary will be
slow to move through the area given front-parallel flow aloft from
the southwest and as such, showers and thunderstorms will be slow
moving/prone to training over the same areas. PW`s will range from
1.75 to 2 inches immediately ahead of the front and showers will
certainly be efficient rain producers. Marginal amounts of
instability ranging from 500 J/KG in the NW Piedmont to upwards of
1500 J/KG will be present ahead of the front although deep layer
shear will only peak around 15-20kts and the severe weather threat
appears to be limited. Taking a look at the grand ensemble of
Canadian, GFS, and EC members, anywhere from 80-90 percent of
members advertise measurable precip across the area late Thursday
morning into the afternoon/evening hours, with a handful of members
suggesting more than 2 inches of rain Thursday afternoon through
Friday morning. 90th percentile NBM QPF is also in this range as
well, and PoPs will be increased a bit during this period. Exact QPF
amounts are still a challenge to pin down but the highest amounts
should fall across the central/eastern portions of NC.

The front will stall across eastern NC on Friday, then slowly
retreat northwestward through the afternoon/evening. While the day
may start off mostly dry, showers will quickly redevelop across the
Coastal Plain and Sandhills by mid morning, then expand
northwestward as the front shifts back over the NW Piedmont. Once
again, nearly 80-90 percent of ensemble members indicate precip
during this period and PoPs will be bumped upward through early
Saturday morning. It`s conceivable an additional 1-2 inches of rain
could occur during this period although it`s hard to say with
certainty where this secondary QPF axis will set up as the front
retreats through the area. Regardless, Thursday and Friday should be
the wettest days of the forecast with periods of heavy rain and
flooding possible. Temps during the day Thursday will remain near or
above normal ahead of the front, turning noticeably cooler on Friday
given cloud cover and rain with highs generally 5-8 degrees below
normal.

Looking at Saturday through Tuesday, ridging over Bermuda will
gradually strengthen and shift westward, resulting in a return to a
fairly typical July distribution of precip chances with the highest
chances across the western Piedmont and a secondary focus area from
sea breeze convection migrating inland. Temperatures will remain
below normal this weekend, gradually moderating closer to normal by
early next week.

&&

.AVIATION /00Z WEDNESDAY THROUGH SUNDAY/...
As of 745 PM Tuesday...

A few thunderstorms are possible around KRDU and KRWI through late
evening, otherwise mainly VFR conditions are expected tonight.

Outlook: Mainly VFR conditions are expected to continue away from
diurnally-driven convection that will gradually increase in coverage
through Wed. A cold front will move into NC late Wed-Wed night, then
become quasi-stationary over the region Thu-Sat. Higher chances of
flight restrictions, both in and away from diurnally-maximized
convection, will consequently result.

&&

.CLIMATE...
Record High Temperatures:

July 17:
KRDU: 100/1887
KFAY: 102/1932

Record High Minimum Temperatures:

July 17:
KGSO: 75/2013
KRDU: 80/1887
KFAY: 77/2019

July 18:
KGSO: 76/1986
KRDU: 79/1887
KFAY: 77/2019

July 19:
KGSO: 75/2016
KFAY: 77/2023

July 20:
KGSO: 75/2019
KRDU: 76/2020

&&

.RAH WATCHES/WARNINGS/ADVISORIES...
Heat Advisory from 11 AM to 8 PM EDT Wednesday for NCZ011-027-
028-042-043-078-089.

&&

$$
SYNOPSIS...MWS
NEAR TERM...CA/MWS
SHORT TERM...Swiggett
LONG TERM...Leins
AVIATION...Badgett/MWS
CLIMATE...RAH