Special Weather Statement, NWS Raleigh, NC

AREA FORECAST DISCUSSION
National Weather Service Raleigh NC
404 PM EDT Wed Sep 22 2021

.SYNOPSIS...
A plume of tropical moisture will remain in place ahead of strong
cold front that will cross central NC tonight. Cool and dry high
pressure will build into the area Thursday through Saturday.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 355 PM Wednesday...

A surface cold front accompanying a deepening, 1003 mb surface low
over ern OH has had little difficulty crossing the Appalachians
today and was analyzed at 1930Z in an arc nearest cntl NC from BCB-
HKY-GMU-MCN. Extrapolation of its movement during the past couple of
hours suggest it will move into Forsyth and Davidson Co. around 22Z.

Generally weak convection/showers now along the front will likely
deepen as they encounter a region of partial clearing and maximized
diurnal heating from cntl and ern SC nwd across the wrn NC Piedmont
and Foothills, where the airmass has become moderately unstable and
characterized by 1500-2500 J/kg MLCAPE. That frontal convection, and
also a few bands of pre-frontal showers/storms developing over the
Piedmont, will exist in an environment characterized by as much as
30-35 kts of effective bulk shear and effective SRH generally around
100-150 m2/s2 - locally higher over the nw Piedmont between 22Z Wed-
01Z Thu. So while a lack of stronger flow through the mid levels,
and also generally weak low and mid level rates, will limit the risk
of severe wind gusts, strong ones up to 40-45 kts will be possible,
as will a non-zero risk of a tornado with local surges/mesovortices
within the frontal convection and also in any discrete cells
immediately preceding it. Thus far, only weak and broad mid-level
rotation has been noted in the pre-frontal band of cells from
Davidson Co. swwd to ern Union Co., but isallobaric forcing related
to 2-3 mb/hr pressure falls preceding the front have not caused the
surface winds to back to sely and elongate and clockwise-curve
hodographs in the lowest couple of kilometers as the models suggest
may occur in the next several hours.

The convection will then gradually diminish in coverage and
intensity as it migrates away from the stronger forcing for ascent
accompanying the deepening mid level cyclone lifting across the OH
Valley, and as it encounters a more stable environment over the ern
half of cntl NC between 01-06Z, where cooling from the earlier band
of convection has occurred today and nocturnal cooling will further
stabilize the environment.

Rainfall amounts are expected to range from 1 to 2" across the srn
and wrn NC Piedmont to 0.25-0.75" across the eastern Sandhills and
Coastal Plain.

While some post-frontal cloudiness/overcast will linger through much
of the night, west to east clearing will occur across the Piedmont
late, with sharply cooler temperatures ranging from mid 50s NW to
mid/upper 60s SE.

&&

.SHORT TERM /THURSDAY AND THURSDAY NIGHT/...
As of 225 PM Wednesday...

The closed low aloft will become vertically stacked with the surface
low over the OH Valley/central Great Lakes Thursday morning. At the
surface, the cold front should be through much of central NC (likely
over the Coastal Plain) early Thursday. The lows will slowly lift
northward through the central Great Lakes through Thursday night as
the cold front continues its eastward progression to just off the
Carolina coast. The upper trough/low will remain to the west of the
area, over and just west of the Appalachians through Thursday night.
There continues to be good model agreement on the position/timing of
the front, thus confidence is fairly high in that regard at this
point. Cool, dry northwesterly flow taking up residence in the wake
of the front as high pressure builds over the mountains from the
west.

Precipitation: Most of the rainfall should be out of the area by
early Thursday and while some rain may be lingering across the
Coastal Plain, do not expect any additional significant rainfall
through Thursday night.

Temperatures: Temperatures should be several degrees lower than
previous days, with highs in the low 70s NW to upper 70s SE and lows
in the upper 40s NW to mid 50s east.

&&

.LONG TERM /FRIDAY THROUGH WEDNESDAY/...
As of 240 PM Wednesday...

Dry weather expected through at least Monday night/Tuesday, with
below normal temperatures Friday/Saturday, gradually moderating
through mid-week.

Cool high pressure centered over the central Appalachians will
remain in place through Friday night as the front stalls off the mid-
Atlantic coast. Aloft, a shortwave will dive southeast out of
central Canada as the previous low lifting northward through Ontario
becomes absorbed by a secondary one moving east through south-
central Canada Friday night. This shortwave will help amplify the
trough to the west as it moves through the Great Lakes and OH Valley
Friday night before lifting northeast through the mid-Atlantic on
Saturday. A weak surface trough may move through the area on
Saturday in response to the shortwave aloft, but the weather should
remain dry. The upper trough will subsequently shift east and
offshore, with NW flow aloft and high pressure at the surface taking
over for Sunday and Monday. Forecast uncertainty increases
significantly beyond Tuesday as the next potential weather system
develops. While rain will once again be possible mid-week, will not
get into specifics at this time.

&&

.AVIATION /18Z WEDNESDAY THROUGH MONDAY/...
As of 215 PM Wednesday...

In between bands of showers and isolated storms now redeveloping
over the Piedmont, MVFR ceilings and pockets of partial clearing to
VFR, and a breezy sely to sly surface wind, will prevail across cntl
NC for the remainder of the afternoon. A forced band of more intense
showers and storms, along a cold front now emerging east of the
Appalachians in NC, will then move east into the NC Piedmont and
affect INT/GSO between 22Z-01Z Thu. That band of showers and storms
will then likely weaken while continuing ewd into the RDU vicinity
between 01-04Z Thu and to FAY and RWI between 03-06Z Thu. Ceilings
will also redevelop and lower into IFR-MVFR range tonight, some of
which will linger until drier air and west to east clearing occur
later tonight through early Thu.

Outlook: Dry, VFR conditions are expected through early next week.

&&

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

&&

SYNOPSIS...MWS
NEAR TERM...MWS
SHORT TERM...KC
LONG TERM...KC
AVIATION...MWS

Hazardous Weather Outlook
National Weather Service Raleigh NC
423 PM EDT Wed Sep 22 2021

NCZ007-008-021>025-038>040-073>076-083-084-232030-
Person-Granville-Forsyth-Guilford-Alamance-Orange-Durham-Davidson-
Randolph-Chatham-Stanly-Montgomery-Moore-Lee-Anson-Richmond-
423 PM EDT Wed Sep 22 2021

This Hazardous Weather Outlook is for central North Carolina.

.DAY ONE...Tonight.

Showers and storms will pose a risk of strong to locally damaging
wind gusts and also heavy rain and flooding through this evening.

.DAYS TWO THROUGH SEVEN...Thursday through Tuesday.

Hazardous weather is not expected at this time.

.SPOTTER INFORMATION STATEMENT...

Spotter activation is not expected at this time.

NCZ009>011-026>028-041>043-077-078-085-086-088-089-232030-
Vance-Warren-Halifax-Franklin-Nash-Edgecombe-Wake-Johnston-Wilson-
Harnett-Wayne-Scotland-Hoke-Cumberland-Sampson-
423 PM EDT Wed Sep 22 2021

This Hazardous Weather Outlook is for central North Carolina.

.DAY ONE...Tonight.

Showers and storms with heavy rain may result in localized, mainly
urban flooding through this evening.

.DAYS TWO THROUGH SEVEN...Thursday through Tuesday.

Hazardous weather is not expected at this time.

.SPOTTER INFORMATION STATEMENT...

Spotter activation is not expected at this time.