535
FXUS62 KRAH 171842
AFDRAH

Area Forecast Discussion
National Weather Service Raleigh NC
242 PM EDT Wed Jul 17 2024

.SYNOPSIS...
A cold front will approach the region on Thursday, bringing showers
and storms to the area. The front will remain stationary through the
end of the week resulting in unsettled weather and cooler
temperatures.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 242 PM Wednesday...

Early afternoon satellite imagery and surface obs depict a weak
NE/SW oriented boundary across central NC, located roughly along US-
1 as of 18Z. Dewpoints east of the boundary remain in the low to mid
70s whereas they have mixed out into the upper 60s to the west.
Along this interface, quite a bit of cu have developed and the first
returns of the day are showing up on radar.  SPC mesoanalysis
suggests nearly 3000 J/KG of MLCAPE on offer eastward into the
Coastal Plain and I would expect these storms to continue to develop
and expand through mid afternoon. There isn`t much in the way of
upper level forcing driving this convection and deep shear remains
relatively weak around 20kts, so I wouldn`t expect much in the way
of severe weather with this line as it moves east but brief periods
of heavy rain and gusty winds are a safe bet with the strongest
storms.

Meanwhile to the west, longwave troughing across the OH valley and
upper level jet dynamics associated with the 120kt 250mb jet over
northern Ohio will help support additional showers and storms across
the western Piedmont later this afternoon into the evening hours. A
few storms have already developed on the mountains and these should
expand/move eastward into the CWA by mid/late afternoon. 12Z HREF
and several HRRR runs maintain convection along and north of I-85
into the evening hours and I will maintain 40-60 PoPs in those areas
through late evening. Meanwhile to the east I`ll keep a few hours of
20-40 PoPs to cover the ongoing convection along the central NC
boundary.

With storms already starting to develop and an increasing veil of
cirrus moving northward, we`re likely at or very close to our
maximum heat index for the day which ranges from around 100 upwards
of 107-108 depending on location (upper 90s in the western
Piedmont). The ongoing Heat Advisory covers things well and may
ultimately be able to be cancelled a few hours early but with
numerous readings still in the triple digits, we`ll leave it as is
for now. It`ll be another mild night tonight with temps falling into
the mid 70s.

&&

.SHORT TERM /THURSDAY AND THURSDAY NIGHT/...
As of 242 PM Wednesday...

Longwave troughing and the attendant surface cold front will move
eastward during the day Thursday, eventually making its way across
the mountains and into NC during the afternoon hours. With
southwesterly flow aloft, the front will make slow eastward progress
as it traverses the state. While the day may start off mostly dry,
showers and storms should quickly develop along the front by early
afternoon. Exactly where storms initiate tomorrow is still TBD but
HREF would suggest somewhere around or just east of the Triad would
be the most favored area. From there, anywhere from 1000-1500 J/KG
will be on offer but once again deep shear remains meager. By this
time upper level support should be displaced well north into New
England although we may still feel the effects of the nearby right
entrance quadrant of the upper level jet. SPC has placed much of NC
within a MRGL risk for severe weather tomorrow, and some of the
stronger storms may be capable of producing gusty winds bordering on
severe thresholds. PoPs will remain generally less than 20 percent
in the morning hours, quickly ramping up to 80-90 percent during the
afternoon.

Given the slow progression of the surface front through the area,
training cells could be a concern. However nearly a week removed
from our last heavy rain event, soils should be able to accept at
least some rainfall before saturating. Isolated flooding of low
lying areas and normally flood-prone locations is a possibility but
we aren`t expecting widespread flooding as this line of convection
moves through the area. HREF PMM QPF indicates 1-2 inches of rain
with the front as it moves through central NC (lesser amounts around
0.50 - 0.75 inches around the Triad, highest amounts across the
Coastal Plain). This fits in with NBM QPF and aligns with the WPC
ERO SLGT risk for Thursday.

As for temperatures, expect highs to range from the upper 80s in the
west to the low/mid 90s in the east. For portions of the southern
Coastal Plain that will reside in the warm sector for most of the
day, heat indices may hit triple digits for a brief time. Elsewhere
the arrival of storms and/or debris clouds should keep heat index
values below Heat Advisory thresholds.  Lows tomorrow bottoming out
in the lower 70s.

&&

.LONG TERM /FRIDAY THROUGH WEDNESDAY/...
As of 142 PM Wednesday...

The extended will continue to feature high rain chances,
particularly in the beginning part of the period into the weekend.
Somewhat lower chances, but still above climo, will exist for the
early to middle part of next week.

On Friday, the cold front approaching from Thu is forecast in most
of the guidance to settle along the NC/SC border, then slowly lift
back north as a warm front Fri night to Saturday evening. During
this time, a trough/shortwave will be present over the TN valley,
fueling energy streaming in from the SSW and PWAT values roughly 120-
percent of normal. Storm chances will remain elevated at this time
with the boundary in place. WPC has retained a slight risk of
excessive rainfall across our SE zones Fri along the stalled front.
A marginal risk remains in place Sat as the front lifts back
northward in the moist southerly flow. Temperatures Fri/Sat look to
top out in the mid to upper 80s, warmest in the south to near 90.
This will be lower than the past several days with added rain
chances and cloud cover.

As we head from Sunday into the middle of next week, the front looks
to become more diffuse and washed out. A Bermuda high will exert
more influence, with continued warm and humid flow persisting.
Aloft, the trough over the TN valleys weakens and a ridge over the
western Atlantic will gradually shift west, resulting in a slight
rise in heights. This should favor a trend toward less rain chances
each day. However, PoPs will remain above climatological normals as
we remain in that moist and unstable environment, as well as with
slight troughing to our west over the Mid-Mississippi Valley
advecting in energy from mid-levels. WPC has another marginal risk
of excessive rainfall over the entire area Sunday. While there may
not be any main surface features, a Piedmont trough and sea-breeze
may enhance storm chances, focused mainly in the afternoon and
evening hours. Highs will largely hover in the mid/upper 80s to
lower 90s, trending warmer by midweek. Heat indices currently look
to stay below advisory criteria given the daily rain chances above
seasonal normals.

&&

.AVIATION /18Z WEDNESDAY THROUGH MONDAY/...
As of 242 PM Wednesday...

Isolated showers and storms are developing east of the Triangle but
have managed to avoid all terminals thus far. FAY/RWI have the best
shot at a storm between now and 21Z although confidence was too low
to introduce in the 18Z TAFs. However to the west, additional, more
robust convection, has started developing and should slowly make its
way through the Triad sites between 21Z and 01Z. The most
significant aviation impacts are likely to remain north of the
terminals but I did include a few hours worth of thunder and gusty
winds in the TAF at INT/GSO. Storms will be in their decaying phase
by the time they approach RDU around 00Z. A few hours of thunder
with a gust to 30kts can`t be ruled out between 00Z - 04Z. Storms
should be done at all sites by 06Z.

Storms on Thursday are likely to hold off until after the end of the
TAF period and have not been included in the 18Z TAFs.

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

&&

$$
SYNOPSIS...Leins
NEAR TERM...Leins
SHORT TERM...Leins
LONG TERM...Kren
AVIATION...Leins
CLIMATE...RAH