Flash Flooding and Flooding in North Carolina, December 17, 2023

Area Forecast Discussion
National Weather Service Raleigh NC
426 PM EST Sun Dec 17 2023

.SYNOPSIS...
A developing storm system over the eastern Gulf of Mexico will move
northeast across northern Florida and emerge off the Georgia coast
early this morning. The low pressure area will intensify as it
moves northeastward along the Carolina coast today and tonight
before moving across the Virginia Capes around daybreak Monday.
Cold high pressure will build into the region on Monday night
and persist through mid week.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 420 PM Sunday...

An MCV and convectively-amplified mesolow/gravity wave and
associated damaging wind gusts, as high as 60 kts measured at FLO,
developed across SC earlier this afternoon and has since moved
across srn NC. Strong mid-level convergence and rapid erosion of the
back edge of the pcecipitation shield have been noted on surrounding
88Ds in the past couple of hours related to that feature, along with
the pronounced surface pressure/wind perturbation. A short-fused
High Wind Warning was consequently issued for the NC Sandhills,
southern Coastal Plain, and portions of the srn Piedmont. We will
continue to monitor observational trends for downstream extension.

Meanwhile, the synoptic surface low has deepened to around 990 mb
just off the cntl SC coast near CHS. This low will continue to deepen
while tracking nnewd across ern NC early tonight and near the coast
of NJ by 12Z Mon.

Rain, heavy at times and with rates enhanced by convective elements
elevated above a stable CAD regime entrenched across all but ern NC,
will gradually end from southwest to northeast overnight. Rapid
runoff may result in poor drainage and urban/creek flooding during
the heaviest rates. Even without the gravity wave signal in forecast
surface winds and gusts, the closest approach, and newd departure of
the deepening coastal low and associated pressure rises and
CAA/steepening of low-level lapse rates, will favor occasional gusts
between 25-35 kts throughout the night.

There will remain a severe risk (wind/isolated tornado) along the
far ern reaches of the RAH CWA/Coastal Plain, ahead of the
approaching synoptic low, where sely flow will advect mid 60s
surface temperatures and dewpoints and support convection rooting
nearer the surface. Aside from that advective warming and
moistening, temperatures to the west and in the CAD airmass will
hold generally steady in 40s-50s through the evening, then be
followed by west to east cooling behind the coastal low and into the
40s, to around 50 in the Coastal Plain by Monday morning.

&&

.SHORT TERM /MONDAY THROUGH MONDAY NIGHT/...
As of 350 PM Sunday...

The phased synoptic trough and briefly closed mid-level cyclone now
developing and deepening across the Savannah Basin will deamplify
and accelerate newd across the srn middle Atlantic through 12Z Mon.
It will do so in response to a "kicker" nrn stream shortwave trough
that will amplify sharply from srn Manitoba and the nrn Plains sewd
and across the OH Valley and cntl Appalachians by 00Z Tue, before it
too will form a closed, mid/upper-level cyclone while pivoting into
the middle Atlantic through 12Z Tue.

At the surface, a tight MSL pressure gradient and CAA will result
Mon, as the coastal cyclone now off the cntl SC coast tracks into
the Northeast. A quickly following clipper cold front will cross
cntl NC Mon evening.

The sensible weather related to the pattern described above will
feature the quick development of strong wnwly surface winds with
diurnal heating/mixing Mon morning, with gusts mostly in the low-mid
30s kts, locally higher across the nrn Piedmont and nrn Coastal
Plain, through midday. Subsidence and mainly sunny conditions in the
wake of the exiting coastal low, and downslope flow/compressional
warming, will favor high temperatures in the 50s, to near 60 in the
Sandhills. The approach/passage of the aforementioned nrn stream
trough axis and clipper surface cold front Mon evening will result
in increasing clouds, to mostly cloudy for a few hours, along with a
small chance of a shower as a shallow cloud/saturated layer deepens
to near minus 8 or 10C (marginally cold for precipitation
production), atop an otherwise dry and residually deeply-mixed
boundary layer around 4 thousand ft deep. CAA, then late night
pockets of decoupling and diminishing surface winds over the wrn
Piedmont, should support lows lows from upr 20s to mid 30s.

&&

.LONG TERM /TUESDAY THROUGH SUNDAY/...
As of 1224 PM Sunday...

Tue-Thu: A deep and vigorous upper-trough extending into the area
from the northern Mid-Atlantic Tue morning will bring a reinforcing
shot of cold advection and gusty northwest winds of 15-25 mph. Tue
looks to be the coldest day of the week with highs some 8-12 degrees
below normal in the low to middle 40s. Cold high pressure over the
TN valley will build into the southern Appalachians by early Wed,
allowing for excellent radiational cooling under clear skies and
light winds. Our coldest night of the week looks to be Tue
night/early Wed with lows in the upper teens to low 20s.

Ridging at mid-levels over the Mid-Mississippi Valley will shift
east Wed night and Thu, keeping our weather quiet and dry as high
pressure at the surface remains anchored over the Carolinas and SE
US. Highs in the upper 40s Wed should trend slightly above normal
Thu into the mid 50s. Lows during this time will generally be in the
20s.

Fri-Sun: A quasi-zonal mid-level flow will largely be in place
during this time. A shortwave over the Midwest and Great Lakes will
track east across our north Fri into Sat, which should increase mid-
high clouds at times. Models show a deeper shortwave trough digging
into the southern Rockies/Plains late in the period Sun, which will
aid the surface high over us to retreat into the far NE US. This
will favor highs remaining slightly above normal in the mid/upper
50s and lows generally in the 30s. While the trough to our SW Sun is
forecast to increase moisture, this appears to not impact our area
until early next week given the latest deterministic/ensemble data,
so have kept Sun dry.

&&

.AVIATION /18Z SUNDAY THROUGH FRIDAY/...
As of 1253 PM Sunday...

24 hour TAF period:

...Expect hazardous aviation conditions over the next 24 hours ...

LIFR to IFR conditions will continue through much of the 24 hour TAF
period as a sfc low deepens and moves northeast along the carolina
coast. Rain rates will likely intensify through this evening as the
low pivots northward but the rain should stay mostly stratiform in
nature. However, there may be a short window between ~23 and 03Z
where isolated thunderstorms may impact both KFAY and KRWI. Overall
though, confidence in this occurring is not overly high at this
point (convection may stay pinned to the coastal areas instead).
Rain should pivot northeast of the area by ~12Z Monday morning. The
return to VFR conditions should follow suit, clearing from west to
east through early to mid Monday morning.

In addition to the LIFR/IFR conditions, ongoing LLWS appears likely
to continue at all TAF sites through much of the 24 hour TAF period.
While sfc winds will start to gust a bit more by early this evening
as the low pulls closer to our area, the flow just above the surface
will continue to be quite strong (~40 to 50kts) and reach LLWS
criteria. By ~12 to 14Z Monday, the flow aloft should weaken enough
to warrant the removal of LLWS in the TAFs.  However, nwly sfc flow
will pick back up early to mid Monday morning with gusts of up to 30
kts possible through the end of the TAF period.

Outlook: Periods of gusty winds will continue Monday and Tuesday. A
brief period of sub-VFR cigs and possibly some virga, are possible
Mon eve/night. Otherwise, expect VFR conditions to prevail through
Thu.

&&

.CLIMATE...
Record Precipitation:

December 17:
KGSO: 1.52/1930
KRDU: 1.35/1890
KFAY: 1.68/1970

December 18:
KRDU: 1.22/1959

&&

.RAH WATCHES/WARNINGS/ADVISORIES...
Flood Watch through late tonight for NCZ007>011-024>028-
040>043-074>078-083>086-088-089.
High Wind Warning until 7 PM EST this evening for NCZ042-
074>078-084>086-088-089.

&&

SYNOPSIS...MWS
NEAR TERM...MWS
SHORT TERM...MWS
LONG TERM...Kren
AVIATION...Luchetti/CBL
CLIMATE...RAH

Hazardous Weather Outlook
National Weather Service Raleigh NC
335 PM EST Sun Dec 17 2023

NCZ042-074>077-084>086-182045-
Johnston-Montgomery-Moore-Lee-Harnett-Richmond-Scotland-Hoke-
335 PM EST Sun Dec 17 2023

...FLOOD WATCH REMAINS IN EFFECT THROUGH LATE TONIGHT...
...HIGH WIND WARNING IN EFFECT UNTIL 7 PM EST THIS EVENING...

This Hazardous Weather Outlook is for central North Carolina.

.DAY ONE...This afternoon and tonight.

Please listen to NOAA Weather Radio or go to weather.gov on the
Internet for more information about the following hazards.

   Flood Watch.
   High Wind Warning.

Heavy rainfall is possible through early Monday morning as a
powerful storm system tracks northeast over the region. Rainfall of
2 to 4 inches will bring the potential for localized flooding,
especially in urban and poor drainage areas. This storm system will
also bring strong to damaging winds, gusting to 40-50 mph at times.

.DAYS TWO THROUGH SEVEN...Monday through Saturday.

Hazardous weather is not expected at this time.

.SPOTTER INFORMATION STATEMENT...

Spotter activation is not expected at this time.

NCZ007>011-024>028-040-041-043-083-182045-
Person-Granville-Vance-Warren-Halifax-Orange-Durham-Franklin-Nash-
Edgecombe-Chatham-Wake-Wilson-Anson-
335 PM EST Sun Dec 17 2023

...FLOOD WATCH REMAINS IN EFFECT THROUGH LATE TONIGHT...

This Hazardous Weather Outlook is for central North Carolina.

.DAY ONE...This afternoon and tonight.

Please listen to NOAA Weather Radio or go to weather.gov on the
Internet for more information about the following hazards.

   Flood Watch.

Heavy rainfall is possible through early Monday morning as a
powerful storm system tracks northeast over the region. Rainfall of
2 to 4 inches will bring the potential for localized flooding,
especially in urban and poor drainage areas. This storm system will
also bring windy conditions, gusting to 25 to 35 mph at times.

.DAYS TWO THROUGH SEVEN...Monday through Saturday.

Hazardous weather is not expected at this time.

.SPOTTER INFORMATION STATEMENT...

Spotter activation is not expected at this time.

NCZ078-088-089-182045-
Wayne-Cumberland-Sampson-
335 PM EST Sun Dec 17 2023

...FLOOD WATCH REMAINS IN EFFECT THROUGH LATE TONIGHT...
...HIGH WIND WARNING IN EFFECT UNTIL 7 PM EST THIS EVENING...

This Hazardous Weather Outlook is for central North Carolina.

.DAY ONE...This afternoon and tonight.

Please listen to NOAA Weather Radio or go to weather.gov on the
Internet for more information about the following hazards.

   Flood Watch.
   High Wind Warning.

Heavy rainfall is possible through early Monday morning as a
powerful storm system tracks northeast over the region. Rainfall of
2 to 4 inches will bring the potential for localized flooding,
especially in urban and poor drainage areas. This storm system will
also bring strong to damaging winds, gusting to 40-50 mph at times.

Lastly, there is a slight risk (level 2 of 5) of strong to severe
storms during the late afternoon and evening. Damaging winds are the
primary severe threat. An isolated tornado is also possible.

.DAYS TWO THROUGH SEVEN...Monday through Saturday.

Hazardous weather is not expected at this time.

.SPOTTER INFORMATION STATEMENT...

Spotter activation is not expected at this time.

NCZ021>023-038-039-073-182045-
Forsyth-Guilford-Alamance-Davidson-Randolph-Stanly-
335 PM EST Sun Dec 17 2023

This Hazardous Weather Outlook is for central North Carolina.

.DAY ONE...This afternoon and tonight.

Rainfall of 2 to 3 inches will bring the potential for localized
flooding, mainly in urban and poor drainage areas. This storm system
will also bring windy conditions, gusting to 25 to 35 mph at times.

.DAYS TWO THROUGH SEVEN...Monday through Saturday.

Hazardous weather is not expected at this time.

.SPOTTER INFORMATION STATEMENT...

Spotter activation is not expected at this time.

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Preliminary Local Storm Report
National Weather Service Raleigh NC
359 PM EST Sun Dec 17 2023

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0304 PM     Non-Tstm Wnd Gst 4 ENE Hope Mills        34.99N 78.88W
12/17/2023  M44 MPH          Cumberland         NC   Mesonet

&&

NTL

Preliminary Local Storm Report
National Weather Service Raleigh NC
400 PM EST Sun Dec 17 2023

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0245 PM     Non-Tstm Wnd Gst 1 SSE East Rockingham   34.90N 79.76W
12/17/2023  M44 MPH          Richmond           NC   Mesonet

&&

NTL

Special Weather Statement
National Weather Service Raleigh NC
405 PM EST Sun Dec 17 2023

NCZ025-040-041-172200-
Chatham NC-Durham NC-Wake NC-
405 PM EST Sun Dec 17 2023

...STRONG THUNDERSTORMS WILL IMPACT WAKE...SOUTHERN DURHAM AND
NORTHEASTERN CHATHAM COUNTIES THROUGH 500 PM EST...

At 405 PM EST, Doppler radar was tracking strong thunderstorms along
a line extending from 10 miles east of Pittsboro to near Cary to 6
miles west of Clayton. Movement was northeast at 15 mph.

HAZARD...Wind gusts up to 50 mph.

SOURCE...Radar indicated.

IMPACT...Gusty winds could knock down tree limbs and blow around
         unsecured objects.

Locations impacted include...
Raleigh, Durham, Cary, Chapel Hill, Wake Forest, Garner,
Fuquay-Varina, Zebulon, RDU International, and Apex.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

If outdoors, consider seeking shelter inside a building.

&&

LAT...LON 3580 7829 3571 7847 3552 7871 3558 7891
      3556 7894 3564 7910 3586 7904 3587 7901
      3599 7900 3599 7899 3601 7862
TIME...MOT...LOC 2105Z 205DEG 14KT 3574 7899 3574 7878 3562 7857

MAX HAIL SIZE...0.00 IN
MAX WIND GUST...50 MPH

Kren