750
FXUS62 KRAH 071511
AFDRAH

Area Forecast Discussion
National Weather Service Raleigh NC
1111 AM EDT Tue May 7 2024

.SYNOPSIS...
High pressure across the western Atlantic will extend into the
Southeast through Thursday as a series of mid to upper-level
disturbances move across the region. A cold front will move
across the region late Thursday into Friday.
&&

.NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...
As of 1100 AM Tuesday...

* Convective coverage should be more limited this afternoon and
  evening than previous days.
* A marginal/Level 1 threat for isolated severe storms remains
  in place this afternoon and evening.

The latest surface analysis shows a stationary front extending west
to east across the OH Valley and into the upper Chesapeake Bay
region. A weak surface trough is noted just east of the Blue Ridge
in western VA and NC. A large region of surface high pressure
extends from the southwestern Atlantic into the southeastern U.S.
The air mass across central NC remains moist with surface dewpoints
in the lower to mid 60s across much of the area with some upper 60s
in the Coastal Plain. Deep layer moisture remains above average with
the morning RAOBS observing PW values in the 1.3 to 1.4 range.
Latest mesoanalysis products note a weakly unstable airmass across
the Coastal Plain and Sandhills with MLCAPE values less than 500
J/Kg and with modest mid level lapse rates. Water vapor imagery
shows a narrow shortwave trough with multiple embedded vortices
embedded in the trough moving across central and eastern VA/NC this
morning.

Forcing for ascent should wane across central NC this afternoon as
the short wave trough moves east and eventually off the coast.
Isolated to widely scattered showers were noted during the mid
morning in the western and southwestern Triad and in the Sandhills
near the SC border. This precipitation appears to be driven on the
back edge of a couple of vortices in the upper trough taking
advantage of a moist environment and perhaps some stronger mid
level flow. Still expect this precipitation to wane and decrease
in coverage as it shifts east and southeast through midday.

A period of little to no precipitation is expected across central NC
during the early to mid afternoon hours as narrow mid-level ridging
aloft moves into the area some downslope flow develops just above
the surface. Expect increasing intervals of sunshine late this
morning into this afternoon which will support destablization with
the airmass becoming moderately unstable. Expect convective
coverage to be less than previous days but with multiple weak
triggers across the area this afternoon and evening, isolated
convection is still possible. These triggers include an
elongated mid-level disturbance associated with earlier
convection in the lower MS Valley that moves through the ridge
axis, some weak convergence along the lee trough and convection
developing across the higher terrain associated with
differential heating.

For this afternoon expect increasing amounts of sunshine. The low
stratus across the western Piedmont will be slow but should
eventually give way to some sunshine. Expect little convective
activity during the early to mid afternoon. CAMs suggest a general
scenario where scattered convection develops to our west during the
mid/late afternoon and makes a run toward the western Piedmont
during the late afternoon and evening hours. Elsewhere, convection
should be isolated with low predictability during the afternoon and
evening. Expect convective coverage to be rather limited into the
overnight as well.

The Marginal/Level 1 severe weather threat is conditional on whether
deep convection develops or moves into the area. Forecast soundings
note that deep layer shear will range between 25-35 kts along with
moderate to strong instability of 2000-2500 J/Kg. Given the profiles
the primary threat should be damaging wind gusts and possibly large
hail with the greatest threat from 3-9pm.

Highs today should warm into the mid 80s across the north and the
upper 80s to near 90 across the south.  Another muggy night is
expected tonight with lows in the mid 60s to around 70. -Blaes
&&

.SHORT TERM /6 AM WEDNESDAY MORNING THROUGH WEDNESDAY NIGHT/...
As of 350 AM Tuesday...

* Summer-like Heat Returns.

* Another Marginal/Level 1 Threat for Severe Storms during the
  afternoon and evening.

Upper ridge centered over the SE US will flatten and shift east and
offshore during the day, which should make the Carolinas more
susceptible to some upper disturbances moving into the region as a
70-80kt subtropical jet punches in from the SW. At the surface, a
lee sfc troughiness will sharpen over western NC.

The first weather headline will be the summer-like heat. Low-level
thicknesses of will be comparable to late June than early May and
will support afternoon highs ranging from upper 80s across the north
to lower 90s over the remainder of the forecast area. When coupled
with the humid BL dewpoints in the mid to upper 60s, heat indices
over the central and eastern portions will be in the mid 90s.

The second weather headline will be another marginal/level 1 threat
for severe storms. Confidence is below average regarding convective
evolution/details Wednesday. However, there appears to be the
potential for two round of storms during the forecast period; 1)
during the early afternoon/early evening which could develop along
old outflow boundary from the previous night; 2) potentially
followed by another round late Wednesday night and into early
Thursday morning from upstream convection moving into the area.

The summerlike heat and humidity will result in moderate to strong
destabilization with MLCAPE of 2500-3500 forecast across the area.
Strong shear of 30-35kts and another favorable high DCAPE
environment will support a primary threat of damaging winds. Large
hail is also possible, given the robust/fat CAPE profiles.

Lows Wednesday night could challenge for the warmest on record with
temperatures in the upper 60s to lower 70s.

&&

.LONG TERM /THURSDAY THROUGH TUESDAY/...
As of 316 AM Tuesday...

The main impacts in the extended will focus on Thu/Fri with a
continued threat of severe weather (mainly Thu) ahead of a strong
cold front. Drier conditions and seasonal to below normal
temperatures are still favored for the weekend into early next week.

A messy and complex weather pattern is shaping up for the period Thu
and Fri. Confidence on specifics is low given the latest trends in
the suite of guidance products and overall synoptic pattern. Broadly
speaking, while the specifics are not clear cut, troughing over the
Midwest to Great Lakes/OH valley Thu is forecast to move east across
the Mid-Atlantic Fri aftn/night before exiting sometime Sat off the
NE US coast. At the surface, low pressure over the OH valley Thu is
forecast to move into the NE US Fri, allowing a cold front to push
through sometime Fri night.

What happens Thu may partially depend on what evolves Wed night to
early Thu morning. Models, particularly the GFS, indicate impulses
of energy tracking across the region on the nose of the left-exit
region of a jet streak near upstate SC. This energy, if it verifies,
would inherit a favorable kinematic and thermodynamic environment
for showers/storms overnight Wed night. This activity could lay an
outflow boundary to start Thu morning. A secondary uncertainty is
upstream convection that will advance into western NC and the
Piedmont Thu morning ahead of the cold front over the TN valley.
Both of these uncertainties could have implications on the coverage
and intensity of storms Thu aftn/evening due to potential rain-
cooled air and convective debris clouds. That said, the environment
in the absence of these competing factors still supports a risk of
damaging winds, large hail, and a few tornadoes with strong low/deep
layer shear and high instability/DCAPE. The CSU/CIPS severe analogs
continue to indicate a wide swath of severe potential from the SE US
into VA. SPC has kept a slight risk (Level 2 out of 5) across the
region. A lee trough will be in place ahead of the front Thu,
favoring a gusty/warm SW flow. Highs could be tricky given the above
considerations, but for now have low 80s NW to near 90 SE.

The severe risk should subside overnight into Fri morning as the
effective front pushes into SE SC. Meanwhile, the cold front looks
to get hung up along the spine of the Appalachians, not moving
through until Fri night. Deterministic/ensemble data still shows
uncertainty on the strength of a secondary shortwave rounding the
base of the main trough, which could bring a secondary shot of
showers/storms Fri aftn/eve. The GFS is particularly robust with
this feature relative to other solutions, tracking a secondary low
along the cold front over eastern NC. We kept showers in the
forecast Fri as a result, but retained the thunder chances mainly
along/east of US-1 as the main instability axis should be confined
along SE NC. Severe weather is not anticipated with this potential
wave. Shower activity should end Fri night as the front pushes
through.

The rest of the period looks to favor more dry time than rain
chances, although precipitation cannot be fully ruled out. It
appears ensemble data is still not in agreement on the placement and
timing of a series of troughs that could impact the region over the
weekend with the NW flow aloft. Rain chances are possible Sat and
Sun, but with lack of consensus in the guidance, we kept most of the
forecast dry with very low-end shower chances at this stage.
Temperatures should return closer to normal and even slightly below
average with highs in the 70s and lows generally in the 50s.

&&

.AVIATION /15Z TUESDAY THROUGH SATURDAY/...
As of 630 AM Tuesday...

Scattered showers and sprinkle will move east across central and
eastern terminals over the next few hours, with little to no
restrictions expected. Any sub-VFR ceilings will be short-lived,
lifting and scattering out, with gusty swly surface wind by ~14-16Z
Tue.

Some additional convection is possible this afternoon and evening,
but should be more isolated/widely scattered in nature and
potentially limited INVOF KINT and KGSO.


Outlook: There will be a chance of mainly afternoon-evening showers
and storms throughout cntl NC through Thu, then ahead of a passing
cold front, mainly at FAY, on Fri.

&&

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

&&

$$

SYNOPSIS...Blaes
NEAR TERM...Blaes
SHORT TERM...CBL
LONG TERM...Kren
AVIATION...CBL