645
FXUS62 KRAH 180626
AFDRAH

Area Forecast Discussion
National Weather Service Raleigh NC
225 AM EDT Thu Jul 18 2024

.SYNOPSIS...
A cold front will approach the region today, 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 810 PM Wednesday...

Expired the Heat Advisory for the day... As the lee trough moves
across the region early this evening showers and storms are possible
over the next few hours. The stronger storms along the VA/NC border
are expected to continue east along the border, with heavy rain and
gusty winds being the main threat. Storms in SC moving into NC is
expected to bring another round of isolated showers and storms to
the Sandhills and southern Coastal Plain region in the next few
hours. The entire area is anticipated to be clear of all
precipitation shortly after midnight. Lows in across the area will
be in the the mid 70s.

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 /SATURDAY THROUGH WEDNESDAY/...
As of 225 AM Thursday...

As the extended forecast period begins, an unseasonably strong upper
low will be over Quebec, with an upper level trough extending south
into the Gulf of Mexico. While the upper low will move east over the
Atlantic Ocean by Monday, the trough will remain nearly stationary
over the Mississippi River valley into next week. Weak southerly
flow will allow continued advection of moist air from the Atlantic
Ocean and Gulf of Mexico, and with the trough to the west acting as
a constant forcing mechanism, showers and thunderstorms can be
expected every day. Went with likely pops Saturday through Monday,
then capped pops at high chance Tuesday and Wednesday because of the
convective nature of the precipitation and uncertainty this many
days out. Most of the region will continue to be under a marginal
(level 1 of 4) risk for excessive rainfall with any stronger
thunderstorms that have high rainfall rates, despite nearly the
entire forecast area being in moderate drought. While the weather
will remain quite humid, daytime highs limited to the upper 80s and
lower 90s with the widespread cloud cover should keep heat indices
under 100 degrees, so no heat headlines are expected.

&&

.AVIATION /06Z THURSDAY THROUGH MONDAY/...
As of 131 AM Thursday...

KRWI and KRDU may experience some residual showers/storms the next
few hours, but overall terminals should mainly remain VFR through
this afternoon.  Scattered to numerous showers and storms are
expected to develop this afternoon and evening, peaking near
KRDU/KRWI/KFAY later today. As such, expect temporary flight
restrictions to develop at these sites at times later today and
tonight.  The bulk of the heavier rain should move east of central
NC late tonight, however MVFR ceilings are expected to fill in over
much of the eastern two thirds of central NC starting near 03Z.

Beyond 06Z Friday: A cold front will sag into and stall across the
region Friday through Sunday which will increase the chances for sub-
VFR conditions through this weekend.

&&

.CLIMATE...

Record High Minimum Temperatures:

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

July 21: KGSO: 76/2011 KRDU: 78/1932 KFAY: 80/2017

July 22: KRDU: 78/2011

July 23: KRDU: 78/2011

July 24: KRDU: 79/2011 KFAY: 79/1945



&&

.RAH WATCHES/WARNINGS/ADVISORIES...
None.

&&

$$
SYNOPSIS...Leins
NEAR TERM...CA/Leins
SHORT TERM...Leins
LONG TERM...Green
AVIATION...Luchetti
CLIMATE...RAH