696
FXUS62 KRAH 181830
AFDRAH

Area Forecast Discussion
National Weather Service Raleigh NC
230 PM 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 /UNTIL 6 AM FRIDAY MORNING/...
As of 1150 AM Thursday...

* Flood Watch expanded southwest to include the Triangle area
 and the Central Coastal Plain.

There was little change to the going forecast for this afternoon and
tonight. Based on 24-hour QPF amounts, areas from Person to Halifax
Counties received some 2-4 inches of rainfall last night. Based on
forecast QPF later today and tonight, 1-3 inches of additional
rainfall is possible. Current 3-hr FFG values in these counties
ranges from 1.5 to 2.5 inches. As a result, localized flash flooding
may occur and we went ahead and issued a Flood Watch until midnight
tonight, collaborating with neighboring offices. Storms appear to
still be relatively fast moving, even with the latest 12Z HRRR, but
given prior considerations from the prior discussion, some training
may be possible, especially over previously saturated ground.

Surface analysis shows the front is draped presently from eastern TN
into portions of WV and central PA. A pre-frontal trough was located
across western NC and into western VA. It still appears convection
will develop along the trough or just ahead of the cold front, with
storms initially being isolated to scattered. That activity is still
expected to become numerous to widespread as they track ESE into the
mid to late evening hours. The main action still looks to be between
about 2 to 8 PM, with most storm activity waning after midnight. The
front will slowly settle along the NC/VA border by sunrise Fri.

Highs this afternoon are expected to be in the upper 80s to lower
90s, as sunshine ahead of storms should allow us to warm up as most
guidance suggests.

If radar and observational trends become more apparent this
afternoon, the Flood Watch may be expanded to include portions of
the Triangle. But as it stands, there was limited confidence to
include these counties.

Lingering convection over the northern Coastal Plain early this
morning will continue to diminish over the next few hours.  Aloft,
water vapor imagery depicts broad swly flow over the southeast
associated with an upper trough currently lifting into the
northeast.

&&

.SHORT TERM /FRIDAY THROUGH FRIDAY NIGHT/...
As of 230 PM Thursday...

The weak frontal zone (more of a sturdy outflow than a true synoptic
cold front) will be pushed to along the E and S edges of the
forecast area by Fri morning, propelled in part by large scale mid
level troughing from New England and the N Mid Atlantic coast SE
across the Ohio Valley and central Miss Valley. The front is likely
to stall there and weaken further through Fri night as a wavy mid
level southern stream southwesterly flow persists, parallel to the
surface frontal zone and on the E side of a mid level trough
extending from SW MI through the Miss Valley to NE TX. The deepest
moisture, in the form of a stream of 2.2-2.4" PW, will be pushed to
across our SE half. While there will not be quite as much upper
divergence as today, the upper jetlet snaking from central TN
through N PA and off Cape Cod and the Canadian Maritimes in
conjunction with passage of a series of minor mid level
perturbations may provide added forcing for ascent, on top of the
favorable thermodynamics (projected SBCAPE of 1500-2000 J/kg),
although deep layer bulk shear will remain rather modest at just
around 20 kts. Given the fairly slow storm motion, the potential for
multicell clusters, and the deep warm layer nearing 4 km, the threat
for locally heavy flood-producing downpours across the SE remains
valid, and this threat will be enhanced in areas that get
considerable rainfall through tonight. Will have highest pops across
the S and SE, but expect above-climo pops areawide. Showers/storms
should have plenty of juice in terms of low level moisture and
warmth to keep moderate CAPE going well into the night, so expect
storms to be maintained through the evening and slow to wind down
overnight. After highs in the 80s to around 90 under variably cloudy
skies, expect lows of around 70 to 75 Fri night. -GIH

&&

.LONG TERM /SATURDAY THROUGH THURSDAY/...
As of 1254 PM Thursday...

The forecast from Saturday onward will feature broad southwesterly
flow aloft as a 594dm H5 ridge remains in place off the southeast
coast. Longwave troughing will stretch from eastern Canada back
through the Ohio valley into eastern Texas next week, with a series
of weak embedded shortwave troughs moving through the flow. This
will allow for daily shower and thunderstorm chances, primarily
during the afternoon and evening hours with a fairly typical
climatological distribution of PoPs (highest values across the NW
Piedmont, Sandhills/southern Coastal Plain). While grand ensemble
model agreement is good for this time period, timing the exact
arrival of any of these shortwaves is a challenge although it looks
like Saturday and Sunday may be particularly wet, with decreasing
chances Monday and/or Tuesday as mid level dry air works in from the
east. A further confinement of the highest PoPs to the NW Piedmont
looks warranted Wednesday and Thursday as the center of the offshore
ridge migrates closer to the coast, but I`ll maintain at least 30-40
PoPs area-wide given the inherent uncertainty in forecasting
convection within low shear environments such as this. The primary
threats with any storms this week should be locally heavy rainfall
as shear and other thermodynamic parameters are largely unsupportive
of widespread severe weather.

Temperatures this weekend into early next week should be within a
few degrees of normal with highs in the upper 80s to lower 90s.
Overnight lows will once again remain on the mild side with readings
generally in the low to mid 70s. With these types of temperatures,
heat indices should generally remain at or just below triple digits
this weekend into next week.

&&

.AVIATION /18Z THURSDAY THROUGH TUESDAY/...
As of 152 PM Thursday...

The threat of showers and storms remain the main challenge for the
immediate near term of the TAFs, followed by low CIG and possible
fog early Fri. Latest satellite and radar imagery reveals that a
trough/boundary extends just south of the GSO/INT terminals. This is
out ahead of a cold front that will move through later tonight into
Friday and settle south of the terminals Fri morning. Given this
boundary, the highest forecast confidence for TSRA is currently at
RDU/FAY/RWI between 19Z and 01Z, earliest at RDU and latest at FAY.
The storm risk may just miss the Triad terminals, but we kept the
TEMPO group in place, between 18Z and 22Z, where confidence is
highest for storm coverage. Storms are expected to move south of the
terminals late tonight as the boundary slides south. As that
happens, guidance shows a strong signal for IFR/MVFR stratus, with
perhaps LIFR early Fri morning. Confidence was too low to introduce
fog but that chance appears highest at the eastern sites along the
front, at RDU/FAY/RWI. Ceilings should lift to VFR by mid to late
morning Fri.

Outlook: Another round of scattered showers and storms are possible
Fri aftn/eve, especially at the south/western terminals of GSO, INT,
FAY. Storm chances will persist in the forecast each day into Tue as
rich moisture and frontal forcing lingers over the area. Morning
stratus or fog is also possible each morning.

&&

.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...
Flood Watch until midnight EDT tonight for NCZ007>011-024>028-
041>043-078.

&&

$$

SYNOPSIS...DL
NEAR TERM...Kren
SHORT TERM...Hartfield
LONG TERM...Leins
AVIATION...Kren
CLIMATE...RAH