855
FXUS62 KRAH 071930
AFDRAH

Area Forecast Discussion
National Weather Service Raleigh NC
330 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 on Wednesday and Thursday. A
cold front will move across the region late Thursday into Friday.

&&

.NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...
As of 305 PM Tuesday...

* Convective coverage should be much 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 but with limited coverage.

The latest surface analysis shows a stationary front extending west
to east across the OH Valley that extends southeast into the
northern Chesapeake Bay. 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
to near 70 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 moderately unstable
airmass across the southern half of central NC with MLCAPE values in
excess of 1500 J/kg while it is more stable to the north near the VA
border with MLCAPE values in excess of 500 J/Kg and with modest mid
level lapse rates. Water vapor imagery shows the slow moving
shortwave trough with multiple embedded vortices beginning to
exit eastern VA/NC.

A period of little to no precipitation is expected across central NC
during much of the afternoon hours as narrow mid-level ridging aloft
moves into the area along with some downslope flow develops just
above the surface. Expect convective coverage to be much less than
previous days. CAMs continue to suggest a general scenario where
scattered convection develops to our west across the higher terrain
over the next few hours with the storms making a run toward the
western Piedmont during the late afternoon and early evening hours.
This convection should wane as it moves east and the evening wears
on. With limited forcing,expect convective coverage to be limited
overnight with noticeably less stratus and fog than previous nights.

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
instability that ranges up to near 2000 J/Kg, especially across the
south and southwest. Given the profiles along with DCAPE values in
excess of 900 J/Kg across the western Piedmont, the primary threat
should be damaging wind gusts and possibly large hail with the
greatest threat from 5-10pm.

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 330 PM Tuesday...

* Severe weather threat has increased with a Slight/Level 2
  threat for severe storms during the late afternoon through
  Wednesday night.
* Summerlike heat and humidity is expected with highs in the
  upper 80s to lower 90s and heat index values in the lower to
  mid 90s in many locations.

A transient and short lived mid-level ridge axis across the
Carolinas early Wednesday morning will shift east and flatten
during the day as a strong and active southwesterly flow extends
from TX across the OH Valley into New England. This strong
southwesterly flow will settle east/southeast closer to the
Carolinas on Wednesday and Wednesday night transporting multiple
disturbances into the TN and OH Valleys that will trigger
clusters of thunderstorms.

SPC has upgraded the severe weather outlook for our area on
Wednesday to a Slight Risk/Level 2 threat. With surface dew
points in the upper 60s to lower 70s and afternoon temperatures
in the upper 80s to lower 90s, the atmosphere will become
moderately to strongly unstable with MLCAPE values of 2000-3000.
Strong deep layer shear of 25-30 kts with a favorable DCAPE
environment will support a primary threat of damaging winds.
Large hail is also possible. Convection allowing models suggest
that there may be two rounds of convection including one during
the mid afternoon to mid evening driven by peak instability,
differential heating and a weak lee trough with a second round
of convection possible during the overnight as convection across
the eastern TN Valley moves across the mountains and into NC.

Wednesday may be and/or feel like the hottest day of the year
thus far in many locations with muggy highs in the upper 80s to
lower 90s and max heat index values in the lower to mid 90s in
most locations away from the Triad and VA border counties. Lows
Wednesday night could threaten record high mins with lows in the
upper 60s to lower 70s. - Blaes

&&

.LONG TERM /THURSDAY THROUGH TUESDAY/...
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.

&&

.AVIATION /20Z TUESDAY THROUGH SUNDAY/...
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...Blaes
LONG TERM...DL
AVIATION...Blaes