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514
FXUS62 KRAH 110042
AFDRAH

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

.SYNOPSIS...
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A cold front will move off the coast of the Carolinas this evening.
High pressure will follow and extend across the Southeast and Middle
Atlantic through the weekend.
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&&

.NEAR TERM /THROUGH TONIGHT/...
As of 235 PM Friday...

Severe storms remain possible across our S half and far E portions
of the central and southern Coastal Plain through early evening.
Large hail and damaging straight line winds are the primary threats.
A severe thunderstorm watch is in effect for this area until 9 PM.

As the morning convection-allowing models strongly indicated, we`ve
seen initiation of deep convection across our SW and in the Coastal
Plain, along the prefrontal trough marking the transition between
the 60s dewpoints to the S/SE and the 40s/50s values to the N/NW.
We`ve managed to blow through this morning`s elevated inversion,
with steep mid level lapse rates nearing 7.5 C/km along with
increasingly favorable mid level flow to 50 mph, while SBCAPE has
risen to 1000-2000 J/kg in the watch area and will likely inch up a
bit higher. The fairly straight and decently long hodographs with
this buoyancy support a large hail threat, along with damaging
straight line wind gusts, as the existing cells are likely to merge
and congeal into short lines or bowing segments. Can`t rule out a
secondary line of convection back with the synoptic cold front,
which is still to our NW, as it pushes SSE through mid-late evening.
This activity should push SE of our area by 9 pm, followed by mostly
clear skies overnight as lower dewpoints surge into the area. Lows
in the upper 40s to mid 50s. -GIH

Earlier discussion from 1010 AM: 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

&&

.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/...
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As of 835 PM Friday...

A cold front and accompanying showers/storms has now cleared all
cntl NC TAF sites and will move offshore through ~02-03Z. In its
wake, nnwly surface winds may remain strong and gusty at times
especially at INT/GSO for a couple of more hours this evening, as
cooler and drier air surges in. VFR conditions, and light and
variable surface winds, are otherwise expected through Sat, as high
pressure builds across the Southeast.

Outlook: A band of rain/showers, from clouds based around 5-6
thousand ft AGL, and with a risk of brief flight restrictions, will
move across cntl NC Sat evening. Rain and IFR-MVFR restrictions,
lowest over the Piedmont at INT/GSO, will overspread cntl NC Tue
morning, with a following chances of showers/storms Tue afternoon
through Wed.
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&&

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

&&

$$
SYNOPSIS...MWS
NEAR TERM...Hartfield
SHORT TERM...Kren
LONG TERM...Swiggett
AVIATION...MWS