-- Discussion containing changed information from previous version are highlighted. --
691
FXUS62 KRAH 071820
AFDRAH

Area Forecast Discussion
National Weather Service Raleigh NC
220 PM 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/...
-- Changed Discussion --
As of 220 PM Tuesday...

* Confidence remains low in Thursday`s severe weather threat.
* Cooler/drier this weekend.

Thursday...
The anomalously deep upper low over the Central Plains will split on
Thursday, with one portion migrating to the Desert Southwest, while
the remaining energy will be absorbed into a trough over the Ohio
Valley.  As this takes place, a potent shortwave trough is forecast
to eject eastward through the Southeast states and into central NC
by mid afternoon. Synoptically, the ingredients should be in place
for strong to severe showers and thunderstorms across the area with
40-50 kts of deep layer shear across the area, PW`s approaching 1.8
inches in spots, MLCAPEs well into the 1500-2000 J/KG range, and a
forcing mechanism in the form of a weak surface trough crossing the
mountains. However, the forecast uncertainty is rooted in how much
early morning convection (leftover remnants from Wednesday`s
Tennessee Valley storms) will disrupt things and stabilize the
atmosphere later in the day. Should the day begin with widespread
stratiform rain and extensive cloud cover, the severe threat in the
afternoon could be lessened as MLCAPEs will likely be considerably
lower. If remnant convection remains to the south or is largely
absent altogether, severe weather will be much more likely.
Unfortunately, how things will play out on Thursday is likely not
going to be clear until late Wednesday.

Confidence is relatively high for rainfall across the area and as
such, I`ll maintain the 60-80 PoPs across the area and work on
pinning down the severe details as we get closer. Temps should reach
the upper 80s to lower 90s but could be a category or two cooler if
cloud cover persists through the day.

Friday...
Friday should see two shortwaves round the base of the
upper trough and move into the area during the late morning/early
afternoon hours. These are in advance of an approaching surface cold
front, which is likely to get hung up west of the mountains and not
arrive until late in the afternoon/evening. As such, PoPs will once
again remain relatively high in the 40-50 percent range area-wide
until the cold front sweeps the anomalously high PW`s off the coast
Friday night. The severe threat looks to be much less on Friday
given the potential for cloud cover and mid level drying although it
would not be surprising in the least to see a few stronger storms
across portions of the Coastal Plain where temps will manage to make
it into the lower 80s. Temps will be a bit cooler to the west, only
topping out in the mid 70s.

Saturday/Sunday...
The upper low will remain north of the area this weekend, with
northwesterly flow taking shape across the Piedmont. While there are
some ensemble solutions advertising widely scattered showers at
times this weekend, downsloping effects would likely greatly limit
these chances and keep them confined to areas of the northwest
Piedmont. PoPs have been trimmed to be 15 percent or less and really
only over the far NW Piedmont locations. Temps should also be
noticeably cooler with highs in the low/mid 70s. Lows in the upper
40s to lower 50s.

Monday/Tuesday...
A southern stream trough will approach the area on
Tuesday. Ahead of the trough, temps will warm back closer to
seasonal normals with highs in the upper 70s to lower 80s. Add about
2-3 degrees to that for Tuesday ahead of the approaching wave which
will also bring about a return of rain chances (20-30 percent PoPs)
to the area.
-- End Changed Discussion --

&&

.AVIATION /18Z TUESDAY THROUGH SATURDAY/...
As of 200 PM Tuesday...

Most of central NC is experiencing VFR conditions this afternoon
although there are some patchy MVFR CIG restrictions in the Triad in
some residual low stratus and across the southern Sandhills. VFR
conditions are expected across most of central NC this afternoon and
tonight as convective coverage will be more limited than during the
past few days. There will be some convection however, a few, light
VFR showers are possible across the northern Coastal Plain through
mid afternoon. Widely scattered showers and thunderstorms are
expected to develop across the mountains this afternoon and this
convection will approach and move into the western Piedmont and
Triad areas late this afternoon and early this evening as they
weaken. The convection should dissipate as it moves east across the
northern Piedmont. Given the limited confidence and coverage will
only include VCSH in the TAFs at KINT and KGSO for now but may amend
later and include a tempo for showers between 22 and 02Z. Mainly VFR
conditions are expected overnight into Wednesday morning with a few
layers of mainly mid and high clouds. Don`t expect much stratus
overnight and just some diurnal cumulus on Wednesday. Southwest
winds are expected through the period, ranging from 6 to 10 kts
today with a few gusts to 16 to 20 kts with a light southwest wind
tonight.

Outlook: Scattered to possibly numerous mainly afternoon and evening
showers and storms are expected on Wednesday and Thursday with
associated CIG and VSBY restrictions. Some storms may be strong to
severe, especially on Thursday. Somewhat more limited convective
coverage is expected on Friday and much quieter conditions with
generally VFR conditions expected into the weekend. -Blaes
&&

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

&&

$$

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