018
FXUS62 KRAH 101718
AFDRAH

Area Forecast Discussion
National Weather Service Raleigh NC
118 PM EDT Fri May 10 2024

.SYNOPSIS...
A cold front moving across the state today will bring a chance for
showers and storms, especially south and east of the Triangle area,
with severe weather possible in our southeast sections. Behind this
front, mostly dry weather is expected with lower humidity and more
seasonable temperatures over the weekend and into Monday. The next
storm system will bring high rain chances Tuesday.

&&

.NEAR TERM /TODAY THROUGH TONIGHT/...
As of 1010 AM Friday...

Forecast tweaks this morning focused on slight spatial and timing
adjustments to hourly precip chances today into the evening. 12z
surface analysis shows a low E off the tip of the Delmarva with a
trailing trough into NE NC, a second trough (dewpoint discontinuity
with shift of weak winds) along the NC Foothills into N GA, with the
actual synoptic cold front still back across central and SW VA, E TN
and N AL/MS. RAP-based mesoanalyses of SBCAPE and the 12z GSO
sounding show well the shallow surface-based stable layer over the
area (contributing to persistent stratus in our SW) with another
inversion around 800 mb, topped by some decently steep (7.0-7.5
C/km) lapse rates through the mid levels that are also noted
upstream. With heating expected to erode the surface stability,
we`re still expecting convection to develop, grow upscale and become
organized into a W-E then WSW-ENE line, starting first in our SW
then spreading across our SE third (where dewpoints will be around
60 or higher) through the afternoon before exiting by mid evening. A
wrench in this scenario is the mature MCS to our S over SE GA and N
FL. The recent CAM runs did not depict the southern bowing portion
racing so far eastward, currently off the SAV coast while most
models have the front edge of this complex about 150-200 m slower/
further W. This system, and its effects on the regional wind field
through ageostrophic adjustments, may play into the evolution and
strength of storms further N over our area, as low level jetting
into our SE could be disrupted, although this actually seems less
likely based on the faster MCS movement, allowing time for air mass
and pressure field recovery in its wake as heating takes place. As
the surface trough shifts ESE today, lower dewpoints will spread
into much of the Piedmont and W Sandhills, limiting the northward
extent of deep surface-rooted convection. Have adjusted pops and
weather to depict lower chances of mainly just showers over the N
Piedmont, transitioning to good chance to likely pops for showers
and storms, some possibly strong to severe across our far S and SE,
peaking in the late afternoon then shifting to our SE in the
early/mid evening. Highs in the upper 70s to lower 80s. -GIH

Earlier discussion from 250 AM: Low pressure is currently over
southeastern Virginia with a cold front extending back to the west-
southwest. There is not a huge temperature gradient along the front,
but there is about a 10 degree spread in the dewpoint. The parent
low will continue to head offshore, with a wave along the cold front
expected to be enhanced during the daytime by an upper level
shortwave. While the forecast still calls for a dry morning, have
bumped up pops to likely across southeastern counties, continuing
with the inherited chance pops elsewhere across the forecast area.
SPC has added a slight (level 2 of 5) risk across portions of
southeastern NC and northeastern SC, including portions of Scotland,
Hoke, Cumberland, and Sampson counties. MUCAPE in this area should
range between 500-1500 J/kg, with greatest amounts to the south.
Effective bulk shear between 30-40 kt will also help to organize any
thunderstorms that do develop. Although an isolated tornado cannot
be ruled out, the primary severe weather threats will be damaging
wind gusts and large hail. The most likely timing for severe weather
appears to be between 2 and 8pm. As the front moves east by sunset,
the chance for showers/thunderstorms will quickly diminish, with all
rain to the east of the region by midnight. Wind gusts will pick up
by late morning and continue through the overnight hours, reaching
as high as 25 mph outside of any thunderstorms that develop. Highs
will range from the mid 70s in the north to the mid 80s in the
south. Lows will be noticeably cooler behind the front, with values
ranging from the mid 40s to the mid 50s.

&&

.SHORT TERM /SATURDAY THROUGH SATURDAY NIGHT/...
As of 1225 PM Friday...

Shortwave ridging will give way to a shortwave digging southeastward
into the Great Lakes, OH valley and northern Mid-Atlantic. While
most of the energy with the trough will remain to our north in VA,
height falls will promote some weak lift in the mid to late evening
hours across our northern counties. At the surface, high pressure
will give way to a lee trough. A secondary cold front or surface
trough will then move through in the evening and overnight hours.
Highs will be some 5-9 degrees below normal in the low to mid 70s,
comfortable for early May. WAA in a return SW flow aloft Sat night
between 850-700 mb will aid some weak (~100 J/kg) instability in the
mid to late evening hours ahead of the trough passage. While most
areas will see more dry time than showers, we introduced a slight
chance of isolated showers across mainly the northeast Piedmont and
northern Coastal Plain, roughly along/north of a line from Raleigh
to Rocky Mount. Any showers will exit by late evening, with lows
dipping a few degrees below seasonal normals into the upper 40s to
mid 50s.

&&

.LONG TERM /SUNDAY THROUGH FRIDAY/...
As of 115 PM Friday...

A period of dry weather and clear skies Sun into early Mon as a
broad shortwave trough will be pivoting across the Northeast and Mid-
Atlantic Sun morning and slide towards the Northeast coast by Sun
evening. Strongly convergent flow aloft will favor strong subsidence
on the backside of the departing trough and transient high pressure
over the area before shifting offshore by Mon morning. Mostly clear
skies and calm conditions will support steep surface inversions and
pockets of radiational cooling and have trended down minimum
temperatures, especially in the typical cool spots (mid 40s to low
50s).

The next chance for rain will be right around the corner as the flat
shortwave ridging and 850 anti-cyclone over the Southeast shift
offshore Mon evening into Tues. A surge in deep southwesterly flow
off the Gulf driven by a closed low spinning through the Mid-MS
Valley will spread anomalous moisture (PWAT 1.3 to 1.6, 90th
percentile) and waves of 700 to 850mb WAA through the southern Mid-
Atlantic. Deep layer moisture appears to be maximized over the area
on Tues, best chance for periods of showers/storms, while Wed may be
a bit more uncertain. A tongue of dry air from 700mb and up will
round the southern side of the shortwave and overspread portions of
the Southeast and southern Mid-Atlantic. Where this dry pocket sets
up will depend on the track of the aforementioned shortwave, which
there area still timing differences on its departure Wed into Thurs.
Nevertheless, will continue to highlight chance to likely PoPs
during this time given the potentially favorable track and
associated synoptic forcing and increased instability, but coverage
may be more limited during this time. Temperatures will be coolest
on Tues (5 to 10 degrees below normal), otherwise highs/lows will be
near to slightly above normal through the remainder of the extended.

&&

.AVIATION /18Z FRIDAY THROUGH WEDNESDAY/...
As of 1205 PM Friday...

Broken MVFR stratus persists over our southwest areas (S of INT/GSO,
W of FAY), but will continue to slowly lift and break up into VFR
clouds. Otherwise, INT/GSO/RDU are likely to remain VFR through much
of Sat, although RDU may see a quick shower or isolated storm 21z-
00z later today. RWI will see better storm chances today, perhaps
two rounds, one chance 19z-21z and again 23z-01z. Finally, FAY has
the highest chance of storms, some possibly severe with damaging
surface gusts and hail, 19z-01z later today. A period of sub-VFR
conditions with strong/shifting winds are possible in and near any
storms. But confidence is high after 03z that VFR conditions will
prevail areawide, lasting through Sat. Surface winds today will be
from the WSW or W shifting to NW the N from northwest to southeast
with cold front passage. later today into tonight, with mostly light
sustained speeds under 10 kts, but a few gusts around 20-25 kts are
possible this afternoon through early evening.

Looking beyond 18z Sat, VFR conditions and dry weather are expected
through at least Mon, within a cooler and less humid air mass,
although brief isolated showers are possible at northern terminals
Sat evening. Rain and isolated storms are expected to overspread the
area starting Tue morning, with a good chance of sub-VFR conditions
lasting into Wed. -GIH

&&

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

&&

$$

SYNOPSIS...Hartfield
NEAR TERM...Hartfield/Green
SHORT TERM...Kren
LONG TERM...Swiggett
AVIATION...Hartfield