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692
FXUS62 KRAH 050648 RRA
AFDRAH

Area Forecast Discussion
National Weather Service Raleigh NC
245 AM EDT Sun May 5 2024

.SYNOPSIS...
A series of mid and upper-level disturbances will overspread and
interact with a front that will remain quasi-stationary over central
NC through early Sunday, then weaken and move northward into VA
later Sunday and Sunday night.

&&

.NEAR TERM /TONIGHT/...
As of 920 PM Saturday...

The models and recent trends in water vapor satellite data indicate
an upr-level, srn stream shortwave perturbation may amplify slightly
as it moves east and across the srn Appalachians and wrn-cntl
Carolinas through early Sunday. Preceding this feature, a long-lived
MCV from convection that developed across LA Fri morning was evident
in regional radar data over the Upstate of SC this evening. This mid-
level feature is forecast to track generally newd, in ~15 kts of
mean swly 700-500 mb flow, and into the srn and wrn NC Piedmont
through early Sunday. It may be preceded by smaller-scale and weaker
MCVs from small convective clusters ongoing from near CLT to CAE to
AGS. The net result will be mid through upr-level forcing for ascent
that will edge newd and across the srn and wrn NC Piedmont (the wrn
half of cntl NC) late tonight-early Sunday.

At the surface, a quasi-stationary front extended at 01Z from near
ECG in nern NC wswwd to near PGV, where it intersected a nne to ssw-
oriented outflow boundary extending through the cntl and srn Coastal
Plain. To the west of that outflow boundary, the front, masked and
modulated by associated rain-cooled air over the rest of cntl NC,
extended across srn NC to a weak mesolow in the Upstate of SC near
GSP. The mesolow will follow a similar path as the parent MCV above
and reach the nw Piedmont/Triad region by 12Z Sun.

While a shallow frontal inversion and weakly stable layer, with a
surface temperature of 60 F, were evident in the lowest couple of
thousand ft AGL in the 00Z-observed GSO sounding, a deeply moist (PW
of 1.5"), saturated, and conditionally-unstable profile was
otherwise present throughout the troposphere. Even slight
modification of observed surface parcels with representative mid/upr
60s preceding the mesolow yields up to several hundred J/kg of
SBCAPE. Associated weak instability, and forcing for ascent as the
mid/upr-level features noted above overspread and interact with the
surface frontal zone, should cause showers and isolated storms to
become increasingly numerous over the srn and wrn NC Piedmont
overnight-Sunday, where a continued Marginal risk of excessive rain
(ie. isolated instances of flash flooding) will remain possible. It
will otherwise be unseasonably mild and muggy, with lows in the 60s.

&&

.SHORT TERM /SUNDAY AND SUNDAY NIGHT/...
As of 215 PM Saturday...

Aloft, the sub-tropical ridge will shift offshore and breakdown
Sun/Sun night as the increasingly sheared shortwave disturbance
moves through the mid-Atlantic and Northeast US. Another southern
stream s/w will strengthen over the southern Plains on Sun, then
move eastward into the lower/mid-MS Valley through Sun night. At the
surface, high pressure will move off the New England coast and
eastward over the northern Atlantic as a low moves through the Great
Lakes and into the Northeast Sun/Sun night. An attendant cold front
draped swwd from the low will become more W-E oriented through the
OH Valley by Sun night. Meanwhile over central NC, the quasi-
stationary front that had lingered over the area will lift northward
as a warm front, with warm, moist southerly return flow over the are
in its wake.

Precipitation/Convection: Showers and storms will likely still be
ongoing Sun morning, most prevalent over the Piedmont. PWATs will
remain anomalously high, in the 1.6 to 1.8 inch range, through the
afternoon. Surface-based instability should increase with daytime
heating, although the latter may be somewhat inhibited by the
ongoing convection and extensive cloud cover. Bulk shear is also
expected to be weak again on Sun. As a result, slow-moving, widely
scattered showers and storms will be possible through the aft/eve
Sun, with the main threat of some isolated heavy rainfall and
localized flooding, although most locations may only receive a few
hundredths of an inch of rain.

Temperatures: Widespread overcast skies and ongoing convection
should somewhat limit heating early, but temps could recover during
the afternoon. For now expect highs to range from the mid 70s along
the NC/VA border to around 80 degrees SE. Lows Sun night mainly in
the low to mid 60s expected.

&&

.LONG TERM /TUESDAY THROUGH SATURDAY/...
As of 245 AM Sunday...

An active pattern persists in the extended, particularly the latter
portion of the week with several chances for showers and storms.
Somewhat drier conditions will start the period, along with
temperatures well above average, followed by near to possibly below
normal highs by the weekend.

Tuesday will feature a weakened shortwave trough from Mon over
VA/NC, with the axis roughly along/east of the Coastal Plain. With
time, the trough will move out over the coast by the evening, with
ridging building in Tue night/early Wed. There is not much forcing
outside of the trough. However, most models indicate weak capping
and 1000-1500 J/kg of MLCAPE, maximized over the Sandhills, eastern
Piedmont and Coastal Plain. This along with 20-25 kt of shear should
favor isolated/scattered activity over the region, which could
interact with a sea-breeze. Suspicion is that activity would be
largely focused east of US-1, but activity could occur just about
anywhere. Highs should turn warmer and above average in the 80s.

Ridging Tue gives way to an increasingly perturbed southwest flow
aloft for the latter part of the week with troughing over the Plains
and ridging over the Gulf. As we go into Wed and especially Thu/Fri,
models/ensembles indicate that the trough will slowly migrate ESE
into the Great Lakes and OH valley region, eventually reaching the
Mid-Atlantic by the weekend. At the surface, lee troughing will
gradually give way to a cold front trying to make its way through
late Fri or early Sat. Upstream convection Wed/Thu over the
Midwest/southern Plain complicate the exact timing/location of these
perturbations in the southwest flow. Shortwave energy could arrive
as early as Wed night, with the GFS/GEFS showing more influence from
the trough versus the EC/GEPS. Better agreement, though, is noted
Thu/Fri where additional perturbations impact the region as the
trough/front inch closer. All of this is to say that we cannot fully
rule out a chance of storms Wed/Wed night, and storm chances will
remain Thu/Fri, albeit with low confidence on timing/location given
model spread on shortwave features. With increasing shear and higher
instability Thu/Fri in the strong kinematic flow, severe storms are
possible ahead of a convectively reinforced boundary slowly sliding
eastward from the TN valley. Wed/Thu should still hover well above
average in the mid/upper 80s to low 90s, though given the
uncertainty in upper-level features, the NBM 90+ degree
probabilities are highest at 50-60% on Wed.

By Sat, model solutions still show spread in the location of the
trough, with the GFS/GEFS/GEPS faster than the EC, which keeps the
main trough over the Great Lakes OH Valley versus near Long Island
in the former solutions. A drier pattern appears favored with NW
flow, but upstream energy in the EC could favor low-end stratiform
rain chances. Highs are currently expected to trend closer to normal
or a touch below in the 70s.

&&

.AVIATION /06Z SUNDAY THROUGH THURSDAY/...
As of 155 AM Sunday...

Upper level disturbances interacting with anomalously moist air in
place will continue to result in adverse aviation conditions
through the forecast period.

A band of showers with some embedded lightning has moved into the
western Piedmont of the Carolinas. This band will progress slowly
eastward through the morning and afternoon hours, and some impact
all terminals through 21z. Additional showers and thunderstorms will
likely develop outside of the primary band, but should be more
scattered in nature through the remainder of the afternoon and
evening.

The ongoing LIFR to IFR ceilings at KGSO, KINT, and KRDU should
spread into RWI over the next few hours. Meanwhile, KFAY could remain
predominately VFR until around daybreak or after, when showers/rain
start to move in from the west. Outside of convection, expect
gradual lifting to VFR at KFAY and KRWI during the late morning and
early afternoon. KGSO, KINT, and KRDU will also show some
improvement, but could very likely remain MVFR through the afternoon
and evening.

Widespread LIFR to MVFR restrictions are expected to re-develop
Sunday evening/night.

Outlook: Scattered to numerous showers and storms are expected again
Monday. Rain chances should become more diurnal and scattered in
nature Tuesday and Wednesday. Continued moist air will support the
potential for restrictions associated with widespread fog and/or low
clouds each morning



&&

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

&&

$$
SYNOPSIS...MWS
NEAR TERM...MWS
SHORT TERM...KC
LONG TERM...Kren
AVIATION...CBL