Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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FXUS62 KRAH 280545
AFDRAH

Area Forecast Discussion
National Weather Service Raleigh NC
145 AM EDT Thu Mar 28 2024

.SYNOPSIS...
An elongated area of low pressure will move slowly east and off the
South Atlantic coast through Thursday morning. The low will then
consolidate and rapidly strengthen while tracking offshore the
Middle Atlantic and southern New England coasts through Friday,
while high pressure otherwise modifies while drifting across the
Southeast.

&&

.NEAR TERM /THROUGH THURSDAY/...
As of 1005 PM Wednesday...

...Flood Watch remains in effect through 8 PM Thu for the NE
Piedmont, Sandhills and Coastal Plain...

Elevated showers/storms, and an accompanying risk of flooding,
especially in urban areas, will gradually edge east and across e-
cntl NC overnight.

A surface frontal zone and elongated area of low pressure now
stretching across the e-cntl Carolinas and ern GA, from near FAY-FLO
to SAV, will continue to move slowly east across the ern Carolinas
and offshore through Thursday morning. Regional radar imagery and IR
satellite data depict a zone of developing and deepening, elevated
convection on the immediate cool/poleward side of that surface
front, in a zone of deeper-layer, low/mid-level frontogenesis and up
to 400-800 J/kg of MUCAPE per SPC mesoanalysis data and the 00Z-
observed GSO sounding. That lift has further maximized over cntl NC
in the past several hours, in a zone of persistent 925-850 mb warm
air advection. Both the WAA and frontogenesis maxima will gradually
edge ewd and offshore through early Thu, as will the elevated
instability supported by the associated saturated or nearly so warm
nose atop stable low-levels. The net result will be the gradual
eastward translation of the band of showers/storms, but with
individual swly cell motions that will at least briefly train and
increase the risk of excessive rain, especially over the the urban
Triangle through ~05-06Z. 40-50 kt of effective bulk shear and
elongated hodographs will also favor a risk of rotating (elevated)
cells capable of producing small hail.


.PREV DISCUSSION... /ISSUED 430 PM EDT Wed Mar 27 2024/

Deep moist southwesterly flow currently persists across central NC,
with PW values in the 1 to 1.5 inch range. This is between a broad
mid/upper trough over the Central and Eastern US and shortwave
ridging just west of Bermuda. Within the trough, a closed mid/upper
low currently over Lake Superior will move NE into southern Ontario
through tomorrow. At the surface, a low pressure system has occluded
near Hudson Bay, dragging a slow-moving cold front to its south that
currently extends down to the Appalachians. Meanwhile, an area of
low pressure is currently over the central GOM with an inverted
trough that extends NE into the Carolinas. This low will move NE
along the GA/SC/southern NC coast tonight, before pushing east of
the Outer Banks by tomorrow evening. This will push a warm front
currently over central SC and extreme SE NC a bit farther north
through this evening. As it does so, high-res models show very
marginal SBCAPE of less than 500 J/kg potentially moving into the
far southern Sandhills and southern Coastal Plain through about 00z.
But the best instability will remain to our south, and radar looks
very unimpressive at the moment, so not concerned about a threat for
severe storms at this time.

As for rainfall, still expecting a general 1-4 inches across most of
the area, highest over the Coastal Plain. The Triad is forecast to
be more in the half inch to an inch range, and there will be a sharp
cutoff on the western side, but exactly where that sets up is still
uncertain as guidance has been waffling back and forth. The 12z HREF
shifted the 2-4 inch axis farther west into central NC to include
the NE Piedmont and Sandhills. While rain is fairly light across the
area at the moment, as the surface low lifts NE and we get
increasing upper divergence from the approaching trough, showers
will pick up intensity and become more widespread later this evening
into the overnight hours. This will result in a risk for flooding,
mainly in urban areas like the Triangle and on some mainstem rivers
which are forecast to reach flood stage at some of our eastern
gauges. Given all of this, the Flood Watch from this evening into
tomorrow evening for the Coastal Plain has been extended farther
west to include the NE Piedmont and Sandhills in addition to the
Coastal Plain. Thunder will be possible with these showers
(especially SE), but convection will remain elevated, so still not
expecting any severe threat. Forecast lows are in the mid-40s to mid-
50s.

As the surface low pulls away to the east, the area of widespread
showers will push to our east as well, clearing the western Piedmont
by early morning, the NE Piedmont and Sandhills by late morning, and
the Coastal Plain by early afternoon. A few showers could linger a
bit beyond that as the potent mid/upper trough swings through, but
dry air will be entering the region from the west by this time as
high pressure starts to build in. Skies will gradually clear from
west to east during the afternoon, but cloud cover should remain for
a good part of the day and when combined with strong northerly winds
on the backside of the low (gusting up to 20-30 mph), it will be a
chilly day. Temperatures will range from lower-50s in the far
NE to lower-60s in the far west. This is anywhere from 5-15 degrees
below normal.

&&

.SHORT TERM /THURSDAY NIGHT THROUGH FRIDAY NIGHT/...
As of 325 PM Wednesday...

Thursday night: In the wake of the offshore surface low, the passage
of the trailing upper trough and a secondary cold front between 00
to 06z Fri will lead to clearing and modest low-level cold dry air
advection. There appears to be sufficient mixing in the BL to keep a
light breeze of 4-7 kts overnight, which should limit the threat for
frost as min temperatures bottom out in the mid to upper 30s.

Friday and Friday night: Heights aloft will steadily increase over
the region as a broad upper level ridge over the Central US builds
eastward. At the surface, a strong pressure gradient between the
rapidly deepening low pressure lifting up the New England coast and
high pressure building east over the Deep South will result in
breezy conditions. Expect frequent NWLY gusts of 20-30 mph, with
occasional gusts as high as 30 to 35 mph, highest across northern
portions of the piedmont and coastal plain counties. The brisk NW
flow will also result in favorable downslope drying/mixing out of
dewpoints  and low-level warming. Afternoon RH values are expected
to fall 25 to 35%, potentially as low as 20-25% across the NW
Piedmont. Fuels will likely be wet enough to avoid elevated fire
weather conditions.

Highs Friday ranging from mid 60s NE to lower 70s south. Lows 40-45.

&&

.LONG TERM /SATURDAY THROUGH WEDNESDAY/...
As of 300 PM Wednesday...

Sat through Sun night: A passing disturbance Sat afternoon will
bring a non-zero chance for some light rain near the VA/NC border,
but mostly expect an increase in cloud cover since the better DPVA
and mid-level WAA remains north of central NC. Otherwise, mid-level
height rises will persist through the weekend in response to a
closed low digging into the Four Corners Region resulting in mostly
dry conditions this weekend with highs rising into the mid/upper 70s
to low 80s.

Mon through Wed: Weak high pressure will build into the northern Mid-
Atlantic late Sun and push a shallow cold front south into VA by
early Mon morning. This boundary will likely represent the southern
extent of some light rain due to gradual moist isentropic upglide
Mon morning. However, the southern extent of the front remains in
question with latest model guidance suite keeping the front up in VA
with the 850mb front well displaced up into northern VA and MD. This
should keep central NC mostly dry through Mon.

By Tue, the now positively tilted trough axis will transport
increasing PWAT values ahead of the trough within the deep
southwesterly flow to around 1 to 1.25 inches over central NC. At
the surface, a deepening area of low pressure will migrate from the
Great Lakes Region into eastern Ontario with secondary cyclogenesis
expected to develop over the northern Mid-Atlantic and drift off the
Northeast coast early Wed morning. There is a high degree of timing
uncertain but this will result in a cold front marching through
central NC sometime between late Tues night and early Wed evening.
Ahead of the front, there will be a chance for showers/storms Tues
and Wed although the character/severity largely remains in question.
Wed will likely have a higher ceiling for severe storms, but will be
completely dependent on the timing of the cold frontal passage and
degree of instability that can develop out ahead of it. Temperatures
will remain unseasonably warm ahead of the cold front with a return
of near normal behind the front into midweek.

&&

.AVIATION /06Z THURSDAY THROUGH MONDAY/...
As of 145 AM Thursday...

24 hour TAF period: Fairly high confidence IFR/LIFR cigs will
prevail through 12Z at the eastern 3 terminals and through at least
06Z in the Triad (KINT/KGSO), with the exception of a few brief
periods of MVFR cigs. Vsbys should generally be VFR or MVFR, with
some brief drops to IFR possible. Showers and scattered
thunderstorms will persist, with the axis of convection slowly
shifting eastward through the night. The rain should start to move
out of central NC during the day Thu and be east of KRWI by 00Z Fri.
Cigs should gradually lift back to VFR from west to east behind the
convection through the morning/early aft, with VFR expected
everywhere by 00Z Fri. Northerly to nely winds should become more
northerly at most terminal tonight, then nwly by Thu aft/eve. There
will likely be periods of gusts in the 16-22 kt range, especially
Thu morn/aft. -KC

Outlook: VFR conditions should prevail through Monday. Gusty winds
of 20-30 kts are expected from the W/NW on Fri and from the SW on
Sat. -Danco

&&

.RAH WATCHES/WARNINGS/ADVISORIES...
Flood Watch from 8 PM EDT this evening through Thursday
evening for NCZ007>011-024>028-040>043-075>078-084>086-088-089.

&&

$$
SYNOPSIS...MWS
NEAR TERM...MWS/Danco
SHORT TERM...CBL
LONG TERM...Swiggett
AVIATION...KC/Danco


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