797
FXUS62 KRAH 160820
AFDRAH

Area Forecast Discussion
National Weather Service Raleigh NC
420 AM EDT Mon Sep 16 2024

.SYNOPSIS...
An area of low pressure centered southeast of Charleston SC early
this morning will drift toward the Carolina coast today and move
onshore tonight. This system will linger and gradually dissipate
across the western Carolinas through mid week. A broad upper low
will linger across the Southeast through the work week.

&&

.NEAR TERM /THROUGH TUESDAY/...
As of 415 AM Monday...

* A strengthening area of low pressure will bring periods of
  rain, heavy at times, to central NC through tonight with a
  swath of 2 to 5 inches of rain across the southern Coastal
  Plain and the Sandhills including Fayetteville with localized
  amounts in excess of 6 inches possible.
* The rain will become widespread later this morning and this
  afternoon and continuing into the evening resulting in a
  difficult evening commute home.
* Winds will increase today across central NC and with gusts
  between 30 and 40 mph at times.
* There is a limited risk of a few tornadoes across the Coastal
  Plain this afternoon and evening, greatest risk ,

Surface low pressure centered about 100 miles southeast of
Charleston SC early this morning is forecast to track northwest
and slowly deepen as the circulation center moves toward the
northern SC coast. The system remains rather sheared and the
latest info from NHC notes that the center lacks definition.
Latest satellite imagery shows the bulk of deep convection to
the north and east of the circulation center. Lightning data
also shows an asymmetric structure with a few deeper bursts of
convection to the northeast of the circulation center. Given
some NWP inconsistency including the GFS which was an outlier
and the weak structure of the system there still remains
considerable uncertainty on whether the system will be able to
become a tropical cyclone or subtropical cyclone before landfall.
There is also some uncertainty regarding the track of the storm
center but the latest guidance from NHC brings the center of
the system across the northern SC coast late this afternoon
and then continuing to the northwest into western NC/upstate SC
by Tuesday evening. This timing and track would spread multiple
hazards across central NC during the next 24 hours. As the
system moves inland, widespread heavy rain and the strongest
winds will shift across the Piedmont this evening and into
western NC late tonight. More scattered precipitation and
decreased winds are expected on Tuesday.

Flooding threat: A swath of 2-5 inches with locally higher
amounts around 6 inches is possible across the southern Coastal
Plain and Sandhills. Isolated to scattered flash flooding still
appears to be the primary threat with this system, especially
in urban and poor drainage locations. Short term rain rates will
be the main discriminator in whether flash flooding occurs,
right now the greatest risk of flash flooding is to the south of
Goldsboro, Raleigh, and Greensboro.

Wind/Severe threat: A tight pressure gradient will strengthen
today as the surface low deepens a bit and moves inland.
Northeast winds will increase with sustained winds of 15-20 mph
this afternoon and evening with gusts between 30-40 mph at
times. At this point, confidence is too low in frequent gusts
over 40 mph, so have opted not to issue a Wind Advisory. There
remains a conditional risk in a few thunderstorms becoming
strong enough to take advantage of more favorable hodographs
this afternoon. Much of this will depend on the evolution of the
environment in the short term and in localized areas. For now,
SPC has kept the marginal risk area unchanged and kept it
focused on the Coastal Plain.


&&

.SHORT TERM /TUESDAY NIGHT THROUGH WEDNESDAY NIGHT/...
As of 245 AM Monday...

Upper level closed low over the Mid-Atlantic region will slowly lift
to the northeast Wednesday becoming more of a trough over the
eastern US later in the week. While the low is lifting to the
northeast, a broad upper level ridge is building across the southern
plains and into the Lower MS valley.

At the surface, models are showing the remnants of the surface low
generally to the west of the region but lingering showers and storms
will be possible Tuesday night and Wednesday especially in the
western half of the CWA. Skies are expected to remain cloudy for
much of the Piedmont with the Sandhills and portions of the Coastal
plain scattering out Wednesday afternoon. Although with all the
moisture still in place, afternoon isolated showers and storms could
develop with daytime heating. For now have 30-40% PoPs across the
region Wednesday afternoon and early evening.

Temperatures Tuesday night will be in the mid to upper 60s across
the region with a few cooler spots in the low 60s. Highs Wednesday
will be a little tricky on depending how much clearing will occur in
the south especially, have temps ranging from upper 70s in the NW
Piedmont to low/mid 80s in the Sandhills and southern Coastal Plain.
Wednesday night temperatures will be once again above average with
overnight lows similar to Tuesday night.

&&

.LONG TERM /THURSDAY THROUGH SUNDAY/...
As of 245 AM Monday...

The remnants of a low pressure system currently off the SC coast
will continue to affect central NC late this week with tropical
moisture and above-climo precipitation chances, highest during the
day with peak heating/instability. However, there remains
considerable uncertainty on the low`s track and placement, with the
latest GFS bringing the surface low north to off the northern Mid-
Atlantic coast by Thursday, while the ECMWF keeps it farther south
in the Carolinas. In any case, above-normal PW values look to
linger, especially if the ECMWF verifies. Looking aloft, mid/upper
troughing will be extended down the Eastern Seaboard. While
confidence on exact coverage and amounts is still low, this supports
a continued wet and unsettled pattern, with POPs in the 20 to 45%
range (lowest SW, highest NE) on Thursday. Given multiple days of
locally heavy rain will have occurred before that, there may be some
more localized flooding concerns.

Additional showers and storms will be possible on Friday, though
coverage should trend downward as the mid/upper trough begins to
weaken. High temperatures on Thursday and Friday will be in the mid-
70s to lower-80s while lows will range from lower-60s to upper-60s,
as the diurnal range is kept down by the clouds and precipitation.

Models show a mid/upper low closing off again and moving back down
into the Southeast US this weekend. However, POPs are only in the
slight to low chance range as surface high pressure ridges down from
New England and brings in some drier air. This will also keep high
temperatures at least slightly below normal given the possible CAD
signal.

&&

.AVIATION /08Z MONDAY THROUGH FRIDAY/...
As of 250 AM EDT Monday...

A developing surface low southeast of the SC coast early this
morning will track northwest toward the northern SC coast by this
evening. As this system draws closer, widespread MVFR CIGS will
lower further and areas of rain and showers will spread northwest
into central NC later this morning with a period of widespread
showers and thunderstorms with IFR CIG and VSBY restrictions at
times spreading into central NC during the afternoon and continuing
during the evening. The worst conditions are apt to move across the
KFAY terminal between about 15Z and 03Z and across the KRDU, KGSO
and KINT terminals between 18Z and 03Z. The widespread heavy rain
will begin to shift northwest of the area toward 06Z.

In addition to the reduced CIGS and VSBYS, northeast winds at 10-15
kts with a few gusts to 20kts early this morning will increase to
northeasterly at 15 to 20 kts with gusts of 30kts at times this
afternoon and evening. In addition, there is the potential periods
of LLWS this afternoon and evening, focused initially near the KFAY
terminal after 16Z and then spreading northwest to KRDU, KGSO and
KINT after around 20Z.

Outlook: As the surface low weakens and lifts into western SC and
NC, the widespread rain and gusty winds will relax on Tuesday and
especially Tuesday night. However, a large mid and upper level
vortex will persist across the Southeast and mid-Atlantic through
the work week leading to the potential for a prolonged period of
possibly adverse aviation conditions in considerable cloudiness,
lowered CIGS and reduced VSBYS in convection. -Blaes

&&

.RAH WATCHES/WARNINGS/ADVISORIES...
Flood Watch from 8 AM EDT this morning through Tuesday morning
for NCZ007>011-021>028-038>043-073>078-083>086-088-089.

&&

$$

SYNOPSIS...Blaes
NEAR TERM...Blaes
SHORT TERM...CA
LONG TERM...Danco
AVIATION...Blaes