477
FXUS62 KRAH 161922
AFDRAH

Area Forecast Discussion
National Weather Service Raleigh NC
322 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 1145 AM Tuesday...

...Dangerous and Near Record Heat To Continue...

...Heat Advisory Remains in Effect from Noon to 8 PM...

An upgrade to Excessive Heat Warning was strongly considered for the
Coastal Plain, given a continuation of record-breaking surface
through 850 mb temperatures observed across the srn Middle Atlantic
the past couple of days. Additionally, mean mixing ratio values have
increased 2 g/kg at RNK and GSO since 12Z Mon, indicative of less
mixing out of afternoon dewpoints today over the Piedmont, while
near steady, 17 g/kg will favor persistence dewpoints over ern NC.
Yet, multi-layered mid/high-level clouds have kept temperatures 2-7
F cooler on average than this time Mon; and these are likely to
persist into the afternoon and may consequently yield slightly lower
hourly and high temperatures, and heat index values, over all but
the srn Sandhills and srn Coastal Plain. Regardless of whether the
heat index values reach 108 or 110 F, it will remain dangerously
hot; and appropriate precautions should be taken.

.PREV DISCUSSION... /ISSUED 330 AM EDT Tue Jul 16 2024/

 There is very little to no change in the synoptic pattern and
antecedent airmass in place as subtropical ridging and Bermuda high
pressure unite to sustain dangerous and near record heat across the
region. Highs will be very similar to yesterday, in 95-100 range,
with heat indices ranging from lower 100s in the NW Piedmont to as
high as 109-110 across interior and eastern/southern portions. As
such, Heat Advisory has been issued for generally the same
climatological divisions across central NC.

PWATs are progged to inch up slightly to around 2.2-2.3" and there
remains a signal in the hi-res models that convective coverage
should be higher than recent days as weak upper impulses emanating
through the ridge and atop lee troughing could potentially help to
drive a west to east moving cluster of showers and storms across
central NC between 18 to 03z. Given the moist environment, some
locally heavy rain rainfall and minor flooding is possible. Also,
given the high CAPE/steep lapse rate environment, cannot rule out an
isolated strong/severe downburst.

Bulk of convection should dissipate by midnight. Balmy overnight
lows in the mid to upper 70s, except for some lower 70s across the
far northern Piedmont counties.

&&

.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 /19Z TUESDAY THROUGH SUNDAY/...
As of 230 PM Tuesday...

While, isolated convection will be possible throughout cntl NC with
continued afternoon heating/destabilization, lift from weak upslope
flow and lee trough convergence may result in multi-cell clustering
and ewd propagation across the Foothills and Piedmont this
afternoon, then probably in a weakening state as it nears RWI and
FAY later this evening. VFR conditions are otherwise forecast
through the 18Z TAF period.

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 16:
KGSO: 99/1915
KRDU: 101/1887
KFAY: 103/1937

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


Record High Minimum Temperatures:

July 16:
KGSO: 75/2010
KRDU: 77/2010
KFAY: 78/1992

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 until 8 PM EDT this evening for NCZ007>011-
023>028-039>043-073>078-083>086-088-089.
Heat Advisory from 11 AM to 8 PM EDT Wednesday for NCZ011-027-
028-042-043-078-089.

&&

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