-- Discussion containing changed information from previous version are highlighted. --
031
FXUS62 KRAH 081954
AFDRAH

Area Forecast Discussion
National Weather Service Raleigh NC
355 PM EDT Wed May 8 2024

.SYNOPSIS...
A series of upper level disturbances will interact with an
unseasonably moist airmass over North Carolina through early Friday,
bringing unsettled weather. A cold front will move across the region
on Friday, ushering in drier and less humid air for the weekend.

&&

.NEAR TERM /THROUGH TONIGHT/...
-- Changed Discussion --
As of 355 PM Wednesday...

Primary focus is on the next several hours, particularly regarding
the severe convective cluster racing toward Charlotte and likely
producing severe wind and hail. This cluster will continue over our
southern counties, feeding on a very buoyant environment with 2000-
2500 J/kg of MLCAPE and improving mid level winds into the 30-40 kt
range spreading in from the W. RAP soundings show fairly steep lapse
rates within the mixed phase region with normalized CAPE nearing 0.2
and a curved and decently long hodograph, supportive of large hail
development particularly as the stronger mid level winds spread in.
And RAP downdraft CAPE downstream of this severe storm is in excess
of 1000 J/kg, suggesting a straight line damaging wind threat. Once
this storm cluster passes through, we`re likely to see a relative
lull in rain coverage, with just a few passing showers and maybe a
disorganized storm or two for a few hours mid to late evening. Then
overnight, additional scattered to numerous showers and storms are
expected to move in from existing and developing upstream convection
(and/or its remnant MCV) now in W KY/TN, with plenty of moisture in
place (PW over 1.5"), high surface dewpoints in the mid 60s to
around 70, steep 850-300 mb lapse rates, and residual elevated
moderate CAPE in place over central NC. After the brief low chance
pop period, will ramp pops back up to good chance to likely esp in
the western 2/3rds of the CWA starting late evening. The severe
threat will be lower overnight, but non-zero, given the trending
favorable mid level flow, increasing low level winds, and lingering
CAPE. Minor flooding is possible with any training cells overnight
as well. Lows 64-71. -GIH
-- End Changed Discussion --

&&

.SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/...
As of 245 pm Wednesday...

* Slight/Level 2 Threat continues into Thursday...

The chance for severe storms on Thursday hinges highly on how
convection evolves tonight. A couple rounds of storms are possible
tonight, the latter of which is expected to be a larger MCS moving
into NC overnight.  That deep convection should overturn the
atmosphere and reduce the currently steep lapse rates aloft and
ultimately reduce updraft strength on Thursday.  However, guidance
isn`t exactly consist on how far east the line will track or how far
north it will extend.  The 12z NAM suggests the storms may weaken
significantly before reaching the coastal plain, and thus forecast
soundings from FAY to RDU and east still show a solid 2000 MLCAPE on
Thursday afternoon.  GFS soundings show a similar profile.

In the wake of the MCS, dying or not, there should also be some
subsidence to subdue convection, but otherwise the trailing outflow
effective front may end up across the southern CWA and serves as a
focus for development, along with lee troughing ahead of the
approaching synoptic front and perhaps even another disturbance
approaching from the Deep South (which models tend to take south
into the Southeast state along with an MCS).

Deep layer shear will continue to be strong as the upper jet edges
eastward along with the upper trough and 500mb winds increase to 40-
50kt.

There is a big discrepancy between the CAMS and the coarser
NAM/GFS/ECMWF.  Most HREF members show every little redevelopment of
convection on Thursday and focus activity across SC and further
southwest, while the NAM/GFS/ECMWF suggest quite a bit of convection
in their QPF.  Tend to lean toward less coverage but with a
conditional severe threat where convection does develop.

Highs should range from the mid 80s nW to around 90 SE.  Lows in the
low to mid 80s.

Friday is another tricky forecast day, as multiple days of possible
convection should continue modify the local airmass, but larger
scale forcing will be better as the positively tilted trough over
the Midwest and Mid-Miss valley today swing east toward the Mid-
Atlantic states.  The limiting factor will be instability given that
the cold front is expected to have shifted across the southern CWA,
with highs dipping back into the mid 70s to lower 80s and lower
dewpoints infiltrating the Piedmont. Again, and conditional threat
for severe storms seems possible but confined to areas closer to the
SC border.

Cooler and drier air is expected behind the front as it finally
pushes through the area Friday, but favor the warmer side of low
temp guidance in the lower 50s for Friday night.


&&

.LONG TERM /SATURDAY THROUGH WEDNESDAY/...
As of 215 PM Wednesday...

Sat begins with broad troughing over generally the Northeast CONUS
characterized mainly by two embedded shortwaves, one of which is
shifting out over the western Atlantic while the second dives ESE
out of Upper Great Lakes and into the Ohio Valley by Sat afternoon.
The former will have shifted the axis of deep, rich moisture (PWAT
~1.6 inches) well offshore and usher in PWAT values around 0.5 of an
inch (near the 10th percentile for GSO, RNK, MHX RAOB) driven by
briefly strong subsidence and downsloping flow WNW flow. The latter
shortwave will pivot across Mid-Atlantic Sat afternoon and evening,
but central NC may only see glancing synoptic forcing from this
feature as the better DPVA remains north of the VA border. Point
soundings suggest shallow afternoon cumulus development to the base
of the subsidence inversion with better 700mb moisture (deepening
the moisture layer) moving into the area late Sat afternoon into the
evening hours. This may be enough to squeeze out some sprinkles over
central NC with better chance for very light rain closer to the
NC/VA border.

Surface high pressure and a secondary area of subsidence on the
backside of the departing trough will lead to dry conditions Sun
through Mon with temperatures in the 70s to low 80s. The next system
will move towards the area Mon night into Wed as a closed low near
the Four Corners Region Sun morning slowly drifts eastward. Closed
lows situated in between a split-flow regime often have timing
issues, and this one is no exception. Latest forecast gradually
brings in precipitation early Tues morning with chances lingering
into Wed with greatest chances diurnally favored during the
afternoon/evening. It would not be surprising to see the quicker
GEFS trend towards the slower EPS and precipitation onset becoming
12 hours later than is currently forecast. Temperatures will trend
back towards above normal mid-level height rises and the 850mb anti-
cyclone shifts offshore.

&&

.AVIATION /18Z WEDNESDAY THROUGH MONDAY/...
As of 140 PM Wednesday...

While VFR conditions will be dominant through this evening across
the area, important details hinge on the path and timing of showers
and strong thunderstorms expected to cross the area, affecting
mostly W and S areas, passing near or over INT/GSO between 20z and
00z, RDU between 22z and 02z, and RWI/FAY 23z to 03z. Sub-VFR
conditions with high/erratic winds, strong gusts, heavy rain, in-
cloud and cloud-to-ground lightning, and hail will be possible in
and near these storms. These storms are likely to be a solid line
and not easily circumnavigable. Behind this line, a few hours of
stratiform rain with embedded isolated lightning may occur, and a
trend toward prevailing MVFR cigs/vsbys is expected overnight, with
lowest confidence at RWI where the occurrence of rain late tonight
is less certain. Late tonight toward sunrise, widespread showers and
isolated storms are possible, keeping cigs/vsbys mostly MVFR at all
terminals with an increase in surface winds from the SW at 10-15 kts
with periodic 15-25 kt gusts.

Looking beyond 18z Thu, high uncertainty in the details of showers
and storms and their impacts lingers through Thu, although fairly
high coverage is expected to persist through the mid to late
afternoon. A lull in shower/storm chances is expected Thu evening
through Fri morning, but the risk of sub-VFR cigs/vsbys with fog is
high 07z-15z Fri. Another chance of showers/storms Fri afternoon and
evening will be focused across the east, all ahead of a cold front.
VFR conditions are expected to prevail Fri night through Mon with
low rain chances and drier weather as high pressure arrives. -GIH

&&

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

&&

$$

SYNOPSIS...Hartfield
NEAR TERM...Hartfield
SHORT TERM...BLS
LONG TERM...Swiggett
AVIATION...Hartfield