317
FXUS62 KRAH 170656
AFDRAH

Area Forecast Discussion
National Weather Service Raleigh NC
250 AM EDT Wed Jul 17 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 250 AM Wednesday...

Water vapor imagery this morning depicts a low-amplitude trough over
the Great Lakes/northeast. More locally, a de-amplified mid-level
ridge remains off the southeast coast. At the sfc, a trough was
observed extending north from the southern Piedmont through the
northern Piedmont.

The upper trough will lift into the northeast this afternoon through
Thursday. While associated upper forcing and shear will maximize to
our north, some mid-level impulses embedded within the swly aloft
will trickle across central NC this afternoon. These features will
help to initiate scattered showers and storms along a pre-frontal
trough that will set up just west of the US-1 corridor. Storms will
generally flow from west to east through the afternoon before
diminishing with loss of heating tonight.  Bulk-layer shear will
peak around 20 kts, but spread relatively uniform across central NC.
A little better shear may develop across the NC/VA border late
afternoon, which may provide a bit better environment for a few
organized clusters to possibly develop.  If any stronger storms can
develop, isolated damaging wind gusts may be possible today.
Additionally, forecasted hodographs/supercell composite fields do
indicate a non-zero chance for perhaps a few supercells to develop
across the central/northern Piedmont into the northern Coastal
Plain.  Not overly concerned with tornado potential today given
relatively high LCLs. However, stronger gust potential may exist
with any isolated rotating updraft that could form later this
afternoon in the areas mentioned. Overall though, the severe threat
today should be relatively localized. A few residual showers/storms
may persist into the overnight period, but overall, rain chances
should wane overnight.

Max temperatures will soar into the mid 90s again today. Afternoon
dew points along and east of the sfc trough (roughly along and east
of US-1) will likely remain in the lower to mid 70s. West of the
boundary, dew points may mix out into the upper 60s. Given the
current position on the sfc trough mentioned above, as well as
latest high-res model trends, decided to expand the Heat Advisory
today a few counties westward.

Overnight lows in the mid to upper 70s are expected once again.

&&

.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. the 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 /06Z WEDNESDAY THROUGH SUNDAY/...
As of 206 AM Wednesday...

VFR conditions will prevail for much of the 24 hour TAF period.
However, scattered showers and storms will develop and spread west
to east this afternoon through tonight. Associated brief sub-VFR
restrictions could develop at any terminal during this period. Any
lingering showers/storms should diminish overnight.

Outlook: Early morning stratus looks possible across the I-95
corridor Thursday.  A cold front will sag into and stall across the
region Thursday through Saturday which will increase the chances for
sub-VFR conditions through this weekend.

&&

.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 this morning to 8 PM EDT this evening
for NCZ008>011-024>028-040>043-075>078-084>086-088-089.

&&

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