341
FXUS62 KRAH 181910
AFDRAH

Area Forecast Discussion
National Weather Service Raleigh NC
310 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 /THROUGH TONIGHT/...
As of 310 PM Thursday...

* Flood Watch remains in effect until late tonight for the Triangle,
  northeast Piedmont, and northern Coastal Plain.
* Severe Thunderstorm Watch remains in effect until late tonight for
  all but Forsyth and Guilford Counties.

Latest satellite and radar indicate that the surface cold front
likely extends from eastern TN into south-central VA. A surface
trough/boundary extends from just SE of the Triad into the northern
Triangle region and the far NE Piedmont into the northern Coastal
Plain. Over the next several hours into the late afternoon, a line
of showers and storms presently over the Triangle and northeast
Piedmont should continue to progress south and east into the central
Coastal Plain into early evening hours. Damaging winds will remain
the primary threat with these storm cells. Mesoanalysis also reveals
a weak surface low over the Triangle. In addition to the severe
risk, the Flood Watch remains in effect and isolated flash flooding
could develop over the next few hours along and east-northeast of
the Triangle as training of storm cells becomes increasingly favored
along the low pressure system. The flood threat should wane by mid
to late evening.

A second batch of storms also exists across far western NC out ahead
of the cold front. The ARW, which has depicted the current placement
of storms reasonably well, shows this activity reach the southern
sections of the Triad into the southern Piedmont and Sandills later
this afternoon and into the mid to late evening. This seems
reasonable given upstream development just west of Charlotte. This
batch will also have the threat of damaging winds. Isolated flash
flooding cannot be ruled out with these line of storms as well but
fast-moving cells should prohibit any flood watch in these areas at
the moment.

Most storm activity should wane by late evening, exiting the Coastal
Plain and Sandhills around midnight or shortly thereafter. Guidance
again favors the development of low clouds and possible fog as the
cold front settles into the NC/SC border by Fri morning. The best
chance of fog would appear to be along/south of the boundary, where
moisture-rich air remains. This would be in the Sandhills to Coastal
Plain region, but perhaps also the Triangle. Overnight lows will dip
into the upper 60s to lower 70s.


&&

.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