558
FXUS62 KRAH 131857
AFDRAH

Area Forecast Discussion
National Weather Service Raleigh NC
257 PM EDT Sat Jul 13 2024

.SYNOPSIS...
A front will weaken over the NC Coastal Plain through this evening.
A strong subtropical ridge will otherwise remain over the Southeast
through early to mid-week.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 1120 AM Saturday...

Hotter, with widely scattered convection possible in both the
Coastal Plain this afternoon and nw Piedmont this evening.

An anomalously strong subtropical ridge, one which this morning
broke daily 500 mb heights at JAX and MFL and will produce
standardized anomalies of 4-5 sigma from the Bahamas to the DR and
Cuba, will remain across the Southeast and swrn N. Atlantic.
Poleward of the ridge and trailing a prominent but compact MCV over
the Middle Peninsula, one related to convection that prompted the
issuance of a Flash Flood Warning over Franklin Co. overnight, a
weak mid-level shear axis will move east across the srn Middle
Atlantic coastal region through this evening.

At the surface, a front and prominent wind shift extended from near
the aforementioned MCV swwd across the NC Coastal Plain this
morning; and this boundary will move little while becoming
increasingly diffuse through this evening. Meanwhile, a weak lee low
may develop near ROA late this afternoon-evening, within a broader
trough forecast to develop just east of the Blue Ridge and which may
drift ewd into the nw Piedmont this evening-tonight.

As morning stratus/stratocumulus over ern and cntl NC lifts and
generally scatters from west to east through this afternoon, weak to
moderate destabilization and weakening convergence along the front
should support the development of scattered afternoon showers/storms
in the Coastal Plain. Additional, weaker cells may develop along and
east of the Blue Ridge and drift into the nw Piedmont before
dissipating this evening. High temperatures were raised slightly
mainly over the srn/wrn Piedmont and wrn Sandhills, where relatively
more-prolonged sunshine today should yield highs in the lwr-mid 90s,
with upr 80s to around 90 more likely across the nrn Coastal Plain
and ne Piedmont, where clouds will be slower to scatter. When
combined with mixed/afternoon dewpoints in the mid-upr 60s over the
nw Piedmont to lwr-mid 70s elsewhere, heat index values in the mid-
upr 90s, to around 100 over the srn half of cntl NC, will result.
After a lingering chance of a shower or storm over the nw Piedmont
this evening, temperatures will settle into the lwr-mid 70s for
most, with patches of altocumulus and fair skies likely.

&&

.SHORT TERM /SUNDAY AND SUNDAY NIGHT/...
As of 257 PM Saturday...

Steady warming trend begins Sun with temperatures rising into the
mid/upper 90s and heat index values ranging from around 100 to near
105. A lee trough will develop over western NC in between an area of
high pressure over the LA riding up into the Ohio Valley and the
anchored Bermuda High in the Atlantic. This will prompt mostly
southwesterly flow at the surface up through 850mb and advect in
warmer temperatures aloft (850mb 19 to 21C). This will support temps
rising into the mid/upper 90s through the early afternoon. Point
soundings indicate some relatively drier air aloft that will mix
down to the surface and keep surface dew points in mid 60s (W) to
low 70s (E). This should temper heat indices a bit, but still reach
around 100 to near 105 degrees. Isolated locations will likely reach
105 during the afternoon for a brief time, but areal coverage and
confidence is low enough to not preclude a heat advisory at this
time.

Some isolated to scattered showers/storms will be possible Sun
afternoon within a hot and humid airmass. Greatest coverage will
likely be along the lee trough in the western Piedmont as a low
amplitude shear axis sags over the area as well as along the
seabreeze, with subsequent showers/storms possible along convective
outflows. Severe potential remains low as deep layer shear remains
weak (around 20 kts) and warm/dry air aloft will work to combat
sustained deep convection. Isolated strong winds cannot be ruled out
if deeper convection is able to develop with a deeply mixed boundary
layer and DCAPE > 1000 J/kg in place.

&&

.LONG TERM /MONDAY THROUGH SATURDAY/...
As of 257 PM Saturday...

The main weather story for Monday and Tuesday will be the intense
heat, given the pattern which features weak ridging and flow aloft,
coupled with H8 temp anomalies of 4-6 deg C above normal.  This will
result in highs in the upper-90s both days, and some low-100s can`t
be ruled out.  Heat indices of 105+ are expected from the Triangle
eastward on Monday, perhaps reaching as far west as the Triad by
Tuesday.  In terms of precip chances those days... coverage should
be isolated at best both days given the overall weak forcing over
the region.

PoPs will increase on Wednesday as heights begin to fall in advance
of a trough moving across the Great Lakes. With increasing flow
above the BL, expect to see the Piedmont trough sharpen and improved
low level convergence and subsequent outflow boundaries should be
the primary lifting mechanisms for increased shower activity. Shower
and thunderstorm activity, which may begin by early afternoon, may
help keep high temps limited to the lower 90s.

Rain chances will continue to increase, with well-above climo PoPs
by Thursday and for Friday and possibly Saturday as well as the
aforementioned trough pushes a cold front into the Mid Atlantic and
Carolinas regions before stalling over us.  That boundary, coupled
with another plume of deep moisture will likely result in several
rounds of heavy rains.  However, that will also keep temps limited
to near-climo values.

&&

.AVIATION /18Z SUNDAY THROUGH WEDNESDAY/...
As of 205 PM Saturday...

Isolated-widely scattered convection will be possible along both a
weakening front near RWI and FAY this afternoon and along and east
of a lee trough that will develop from the Blue Ridge to the
Foothills and nw Piedmont (INT/GSO) through this evening. While
patchy fog will be possible at RWI Sun morning, the signal in model
guidance for such development is low.

Outlook: Aside from a 10-30% chance of diurnally-driven convection,
VFR conditions are expected until the next front settles into the
region with higher chances of convection and flight restrictions
late Wed-Thu.

&&

.CLIMATE...
Record High Temperatures:

July 15:
KGSO: 97/1974
KRDU: 99/1997

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


Record High Minimum Temperatures:

July 12:
KGSO: 76/2011
KRDU: 78/2011
KFAY: 80/1935

July 13:
KGSO: 75/2017
KRDU: 78/2017
KFAY: 78/2017

July 14:
KGSO: 77/1981
KRDU: 77/2017
KFAY: 80/2017

July 15:
KGSO: 74/2019
KRDU: 76/1992
KFAY: 78/2015

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

&&

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

&&

$$
SYNOPSIS...MWS
NEAR TERM...MWS
SHORT TERM...Swiggett
LONG TERM...np
AVIATION...MWS
CLIMATE...RAH