286
FXUS62 KRAH 170750
AFDRAH

Area Forecast Discussion
National Weather Service Raleigh NC
350 AM EDT Tue Sep 17 2024

.SYNOPSIS...
An area of low pressure centered across far northeast South Carolina
will drift west into upstate South Carolina tonight. The remnants of
this system will linger and gradually dissipate across the mid-
Atlantic through the end of the work week.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 335 AM Tuesday...

* Last large band/region of showers and storms spreading across the
  northern Coastal Plain and the northern Piedmont.
* Flooding threat has abated and Flood Watch will be cancelled.

The latest surface analysis shows the center of the surface low
located



Latest sfc analysis depicted the center of the low near Florence, SC
this evening. Thus far, rain rates have been more so "moderate" than
"heavy" in general. There has been a few heavier cells (one such
cluster moving through the Triangle now) throughout the day, but
overall, the heaviest rain has mostly remained closer to the coast.
A continuous "feeder" band of deeper moisture and heavier cells
continues to move slowly north along the Crystal Coast and southern
OBX.  Simultaneously, a deformation zone of sorts has developed west
of our area over the CHarlotte metro area. Latest high-res guidance
suggests that these two features will likely remain outside of
central NC through the overnight period. Consequently, the highest
remaining QPF through tonight should largely stay east and west of
our area. Nonetheless, given the anomalous moisture and continuation
of moderate rainfall, will maintain the Flood Watch for all of
central NC at this forecast update.

Thus far, rotating cells have largely remained near or just inland
of the coast today. As the aforementioned feeder band pivots north
over the Inner and Outer Banks, we`ll continue to have a non-zero
chance of an isolated shallow tornado for those in the far eastern
Coastal Plain. With time, however, the low should occlude (already
signs that this is beginning as of 01Z), and our area should be
mostly removed from the warm, more unstable air.  Thus, the low-
probability tornado threat should diminish with time overnight. The
latest HRRR runs paint this scenario, shunting all low-level
helicity swaths to our east across the inner/outer banks.

Rain chances will slowly decrease from south to north through day
break. As the low continues to weaken over land, the sfc gustiness
should diminish some through daybreak Tuesday morning as well.
Otherwise, overnight lows in the lower 60s (west) to around 70
(east).

&&

.SHORT TERM /TUESDAY THROUGH TUESDAY NIGHT/...
As of 212 PM Monday...

The remnant surface low is projected to be somewhere over north-
central to northwest SC at the start of the period. The system will
continue to track west-northwestward during the day/night, occluding
and filling, weakening as it does so. While the mid-level dry slot
is forecast to lift through during the morning and afternoon from
south to north, continued moisture transport from 925-850 mb will
remain in place, especially along and north of US-64 and into the
northwest Piedmont. As such, highest shower chances during the day
will be in these areas, with lower chances across the southern
Piedmont, Sandhills, and southern Coastal Plain. Wind gusts will be
highest in the morning, between 20 and 30 mph and some occasional
gusts to 35 mph, along and north of US-64 and over the Triad. Gusts
should then start to weaken by the afternoon and evening as the low
occludes and the pressure gradient relaxes. Additional rainfall
amounts one to three quarters of an inch are possible along/north of
US-64, with a tenth of an inch or less across our southern counties.
Some isolated spots of the Triangle to north of US-64 could be
higher per the 12z HRRR/HREF with any training storms, which is
consistent with WPC`s marginal excessive rainfall in this area.

As for severe potential, SPC currently is not highlighting any area
of concern. There does remain, however, a chance of some low-topped
supercells capable of brief tornadoes mainly east of I-95 and north
of US-64, roughly from a line east of Raleigh to Rocky Mount to
Roanoke Rapids. This corridor appears most favored for instability
coupled to stronger low-level shear. It would appear the threat
would be from the morning hours into midday. Thereafter, the low-
level wind field lessens, thereby reducing the severe threat.

Highs Tue should be in the low 70s over the far NW, including the
Triad, to the upper 70s to near 80 along/east of US-1. Rain chances
should lessen by evening/overnight as the low weakens and activity
shifts into VA into far western NC, with lows in the low to mid 60s.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/...
As of 345 AM Tuesday...

Mid/upper troughing will extend down the Eastern Seaboard including
into central NC from Wednesday night into Thursday. Meanwhile a
surface low will linger off the northern Mid-Atlantic coast. This
will bring one last day of upper forcing for ascent and above-normal
PW values, so POPs on Thursday are generally in the 30-40% range,
highest east and maximized during peak heating. There could be
enough instability for a few storms. QPF amounts in the models are
not impressive, so not concerned about an additional heavy rain
threat, and looks fairly low impact overall.

As a mid/upper ridge over the Plains begins to move east on Friday,
it will begin to push the trough east and offshore. This will result
in NW flow and much drier air moving into central NC, with PW values
trending below normal. At the surface, high pressure will gradually
nose down from SE Canada into the Mid-Atlantic from Friday into
Monday. Overall this pattern supports limited rain chances at best,
which is a significant change from last night when the models
depicted the mid/upper low moving back south across the area. Now,
they keep it and the associated surface low well to our east in the
western Atlantic. Instability looks minimal to non-existent as well
given the cool wedge of high pressure and NE flow near the surface.
The best chance for clouds and isolated showers looks to be in the
Coastal Plain closer to the low and where there will still be moist
onshore flow in the low levels, but even there POPs are only slight.
The GFS does try to bring a shortwave through the area on Sunday, so
POPs are slight that day areawide.

As for temperatures, highs should be within a few degrees of normal
from Thursday through Saturday, in the upper-70s to lower-80s. Lows
will gradually trend downward as the air mass turns drier, from mid-
to-upper-60s on Wednesday night to upper-50s to lower-60s by
Saturday night. On Sunday and Monday when the cool wedge of high
pressure really takes hold, forecast highs are only in the 70s with
lows in the mid-50s to lower-60s. If the raw GFS is to be believed,
some places won`t even get above the 60s on these days, but would
like to see more support from ensemble guidance before buying into
this too much.

&&

.AVIATION /06Z TUESDAY THROUGH SATURDAY/...
As of 230 AM EDT Tuesday...

Widespread MVFR to IFR conditions primarily from low CIGS are noted
across central NC early this morning. CIGS are expected to lower
during the pre-dawn hours leading to IFR/LIFR conditions across much
of the area through the mid morning hours. A broad area of light
rain showers with a few embedded heavier showers extend from the
central and northern Coastal Plain west across the northern
Piedmont. This area of precipitation may also result in reduced
VSBYs at times as the overall rain axis shifts north through the
morning. An isolated thunderstorm is possible across the central
Coastal Plain, near but mainly south of the KRWI terminal. Low CIGS
are expected to persist for much of the day although cloud bases
will lift during the late morning and early afternoon with MVFR CIG
restrictions still commonplace during the afternoon. Some brief
improvement with VFR CIGS are expected late in the afternoon across
the Coastal Plain and Sandhills impacting the KRWI and KFAY
terminals. There is a limited risk of additional showers and perhaps
a storm this afternoon primarily near KINT/KGSO and KRDU. Another
round of MVFR to IFR CIGS are expected to return tonight and
continue into Wednesday morning.

A low pressure area is expected to track northwest across northern
SC through tonight. This will maintain a northeasterly surface wind
with gusts of 15 to 25kts at times overnight, perhaps a little
stronger in the Triad. Winds should begin to diminish from south to
north later this morning and especially this afternoon. A prolonged
period of LLWS should be relaxing early this morning. Recent data
from the WRAL tall tower southeast of Raleigh shows wind speeds
aloft at 2kft beginning to weaken. Will maintain a mention of LLWS
in the TAFs through around 09Z with the greatest risk of LLWS
condition in the Triad.

Outlook: After another period of IFR/LIFR CIGS early Wednesday
morning, an unsettled period will continue through Thursday with
area of late night and early morning stratus and a risk of some
afternoon showers and possibly a storm. Aviation conditions will
generally improve on Friday and Saturday. -Blaes

&&

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


&&

$$

SYNOPSIS...Blaes
NEAR TERM...Luchetti
SHORT TERM...Kren
LONG TERM...Danco
AVIATION...Blaes