Flash Flood and Hail in North Carolina, August 15, 2023

Area Forecast Discussion
National Weather Service Raleigh NC
156 PM EDT Tue Aug 15 2023

.SYNOPSIS...
A cold front will settle across the middle Atlantic and west-central
Carolinas this afternoon through tonight, then stall over the east-
central Carolinas on Wednesday.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 150 PM Tuesday...

Update: A Severe Thunderstorm Watch has just been issued for all of
central NC through 9pm tonight.

Previous discussion from 420 AM Tuesday: The Heat Advisory has been
upgraded to an Excessive Heat Warning for the NC Coastal Plain, ern
Sandhills, and Wake Co., effective from 11 AM to 7 PM. A Heat
Advisory otherwise remains in effect for the southern Piedmont,
western Sandhills, and a portion of the northeast Piedmont of
central NC; and it has been expanded to include Stanly Co.

A closed mid/upper-level cyclone over the srn Lake MI and swrn Lower
MI vicinity will move ewd across nrn OH and Lake Erie today, then
weaken and become an open wave trough while pivoting newd across
nwrn PA and NY tonight. An associated, positive-tilt synoptic trough
will extend from that perturbation swwd and across the OH and lwr MS
Valleys by 12Z Wed. While the most concentrated height falls and
forcing for ascent will precede the weakening cyclone across the
cntl Appalachians and nrn middle Atlantic today, glancing height
falls and weakly perturbed and convectively-amplified swly flow
aloft will result across the Carolinas and srn middle Atlantic. A
belt of 30-45 kts of mid-level flow will maximize across the nrn and
wrn NC Piedmont, with stronger flow and effective shear magnitudes
likely to the north, across VA.

At the surface, a trough in the immediate lee of the srn-cntl
Appalachians this morning will migrate ewd and across the srn middle
Atlantic Foothills and Piedmont this afternoon. Incipient convection
along that trough, and associated aggregate outflow, may result in
the development of an effective cold front that will cross cntl and
ern NC through this evening. A trailing, synoptic cold front will
follow and cross cntl NC, at least into the I-95 vicinity, by 12Z
Wed.

Temperatures today will be comparable to, to perhaps another degree
or two hotter, than Mon, while surface dewpoints this afternoon will
be similarly in the lwr-mid 70s. Given that heat index values in a
large portion of the Heat Advisory reached or exceeded 110 F on Mon,
the Advisory for today has been upgraded to an Excessive Heat
Warning for the NC Coastal Plain, ern Sandhills, and Wake Co.

Those hot temperatures will support moderate to strong
destabilization today, with cooling temperatures and steepening
lapse rates aloft that will result from the approach of the
aforementioned synoptic trough and height falls. Initially scattered
scattered showers/storms are expected to develop with that
heating/destabilization along the ewd-migrating lee trough over the
Foothills and wrn Piedmont by early this afternoon, while isolated
cells may develop in a more weakly and nebulously-forced environment
to the east. The aforementioned belt of swly mid-level flow will
favor a mix of line segments and discrete cells capable of damaging
wind gusts and hail, with the latter favored in discrete cells.
Convection may have a tendency to backbuild along the advancing
surface trough and subsequent outflow, given generally
unidirectional/swly deep-layer flow and weak upwind propagation
vectors. The moderate to strong instability, amid a plume of PWs
around 2", will consequently also favor high rain rates and a risk
of excessive rain/flash flooding.

Lead convection and trailing "stratiform" rain may be slow to exit
the Coastal Plain tonight; and the approach/passage of the synoptic
front will support a slight chance of redevelopment of weaker
showers/storms overnight-Wed morning. Most areas will experience
rain/diabatically-cooled lows in the mid-upr 60s west to lwr 70s
east, with patchy fog possible as skies partially clear on the back
edge of the lead convection and cloud band.

&&

.SHORT TERM /WEDNESDAY AND WEDNESDAY NIGHT/...
As of 330 AM Tuesday...

As an upper level shortwave lifts through the Northeast, the SW-NE
oriented longwave trough will linger from the Lower MS Valley to the
Great Lakes/Northeast. A pair of highs will bookend the trough,
Bermuda high to the east and high pressure over the Intermountain
West to the west. At the surface, the old front will linger from the
FL Panhandle to the NC coast as a quasi-stationary boundary, with
high pressure over the OH/TN Valley ridging eastward into central
NC. Generally expect the best chances for diurnal showers and storms
along and east of the surface boundary where the best moisture
(around 1.5 inches) and instability (MUCAPE around 1000 J/Kg) will
be. Effective shear should max out around 20 kts. Highs should
generally peak in the mid 80s to around 90 degrees, though they
could be limited somewhat in the east depending on when/where
convection gets going. Lows Wed night in the mid 60s to low 70s
expected.

&&

.LONG TERM /THURSDAY THROUGH MONDAY/...
As of 405 AM Tuesday...

Thursday and Friday: An upper low will trek eastward from Ontario
Canada Thu/Thu night and Quebec Fri/Fri night. The attendant trough
will amplify southward through the Great Lakes on Thu, through the
OH Valley into the mid-Atlantic Thu night. The trough will then lift
slowly NNE out of the mid-Atlantic as the low moves through the
Northeast US/Quebec, Canada Fri/Fri night. Behind the trough, the
high over the Four Corners Thu will migrate eastward into the
southern Plains Thu night/Fri. The sub-tropical ridge should extend
northward through the Plains to the US/Canada border on Fri. At the
surface, the quasi-stationary boundary will linger invof the NC
Coastal Plain Thu/Thu night, with a trough sitting over the
Piedmont. A cold front will approach from the north-northeast on
Fri, pushing southward through central NC Fri night. The best chance
for diurnally driven showers and storms Thu will again be across the
Coastal Plain, Sandhills, and possibly over the eastern Piedmont.
Fri/Fri night should be dry, with the exception of the southern
Coastal Plain. Highs Thu should be similar to Wed, mid 80s to low
90s, increasing a couple/few degrees in some places for Fri. Lows
generally in the mid 60s to low 70s expected.

Saturday through Monday: Aloft, high pressure centered over the
central Plains/mid-MS Valley will likely build, expanding to
encompass much of the central and eastern CONUS over the weekend and
into Mon. At the surface, the front will likely lift back northward
as a warm front on Sat, while relatively cool high pressure drifts
eastward from the OH Valley into the mid-Atlantic Sat/Sat night. The
high should shift offshore Sun/Sun night with a trough again setting
up over the region on Mon. Highs in the mid 80s north to low 90s
south on Sat will moderate back into the low to mid 90s by Mon. Lows
should generally be in the mid 60s to low 70s.

&&

.AVIATION /18Z TUESDAY THROUGH SUNDAY/...
As of 140 PM Tuesday...

Isolated TSRA are now developing across the region, and will
increase in coverage from NW to SE this afternoon and evening.
Storms will be strong to potentially severe, with damaging wind
gusts and large hail as the main threats. Surface winds will be
gusty and erratic near storms, with strong up/downdrafts expected.
Once storms exit to the southeast tonight, MVFR ceilings and VIS may
develop across the southern half of the region, mainly near KFAY. VFR
conditions are expected early Wed.

Outlook: A chance of diurnally-driven convection and morning
stratus/fog will linger especially at ern terminals (FAY/RWI)
through the end of the week, as a front stalls and weakens there.

&&

.CLIMATE...

Record max temperatures and high minimum temperatures today.

RDU     Record Max/year  Record Hi Min/year
08/15    99    2007      77    1995

GSO     Record Max/year  Record Hi Min/year
08/15   100    1918      77    1995

FAY     Record Max/year  Record Hi Min/year
08/15   100    1935      78    2017

&&

.RAH WATCHES/WARNINGS/ADVISORIES...
Heat Advisory from 11 AM this morning to 7 PM EDT this evening
for NCZ010-024>026-040-073>076-083-084.
Excessive Heat Warning from 11 AM this morning to 7 PM EDT
this evening for NCZ011-027-028-041>043-077-078-085-086-088-
089.

&&

SYNOPSIS...MWS
NEAR TERM...MWS/JJT
SHORT TERM...KC
LONG TERM...KC
AVIATION...JJT
CLIMATE...Blaes

Hazardous Weather Outlook
National Weather Service Raleigh NC
152 PM EDT Tue Aug 15 2023

NCZ007>009-021>023-038-039-161800-
Person-Granville-Vance-Forsyth-Guilford-Alamance-Davidson-Randolph-
152 PM EDT Tue Aug 15 2023

...SEVERE THUNDERSTORM WATCH 649 IN EFFECT UNTIL 9 PM EDT 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.

   Severe Thunderstorm Watch.

.DAYS TWO THROUGH SEVEN...Wednesday through Monday.

Hazardous weather is not expected at this time.

.SPOTTER INFORMATION STATEMENT...

Spotter activation will likely be needed.

NCZ010-024>026-040-073>076-083-084-161800-
Warren-Orange-Durham-Franklin-Chatham-Stanly-Montgomery-Moore-Lee-
Anson-Richmond-
152 PM EDT Tue Aug 15 2023

...HEAT ADVISORY IN EFFECT UNTIL 7 PM EDT THIS EVENING...
...SEVERE THUNDERSTORM WATCH 649 IN EFFECT UNTIL 9 PM EDT 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.

   Heat Advisory.
   Severe Thunderstorm Watch.

.DAYS TWO THROUGH SEVEN...Wednesday through Monday.

Hazardous weather is not expected at this time.

.SPOTTER INFORMATION STATEMENT...

Spotter activation will likely be needed.

NCZ011-027-028-041>043-077-078-085-086-088-089-161800-
Halifax-Nash-Edgecombe-Wake-Johnston-Wilson-Harnett-Wayne-Scotland-
Hoke-Cumberland-Sampson-
152 PM EDT Tue Aug 15 2023

...EXCESSIVE HEAT WARNING IN EFFECT UNTIL 7 PM EDT THIS EVENING...
...SEVERE THUNDERSTORM WATCH 649 IN EFFECT UNTIL 9 PM EDT 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.

   Excessive Heat Warning.
   Severe Thunderstorm Watch.

.DAYS TWO THROUGH SEVEN...Wednesday through Monday.

Hazardous weather is not expected at this time.

.SPOTTER INFORMATION STATEMENT...

Spotter activation will likely be needed.

JJT

Special Weather Statement
National Weather Service Raleigh NC
126 PM EDT Tue Aug 15 2023

NCZ007-023>025-151800-
Durham NC-Alamance NC-Person NC-Orange NC-
126 PM EDT Tue Aug 15 2023

...A strong thunderstorm will impact portions of central Alamance,
Person, Orange and northwestern Durham Counties through 200 PM EDT...

At 126 PM EDT, Doppler radar was tracking a strong thunderstorm near
Baynes, or near Prospect Hill, moving northeast at 40 mph.

HAZARD...Winds in excess of 40 mph and pea size hail.

SOURCE...Radar indicated.

IMPACT...Gusty winds could knock down tree limbs and blow around
         unsecured objects. Minor damage to outdoor objects is
         possible.

Locations impacted include...
Durham, Chapel Hill, Burlington, Graham, Roxboro, Hillsborough,
Mebane, Rougemont, Concord and Haw River.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

If outdoors, consider seeking shelter inside a building.

&&

LAT...LON 3647 7880 3601 7880 3591 7933 3610 7949
      3625 7948 3624 7915 3648 7914
TIME...MOT...LOC 1726Z 244DEG 33KT 3620 7927

MAX HAIL SIZE...0.25 IN
MAX WIND GUST...40 MPH

AS

Special Weather Statement
National Weather Service Raleigh NC
206 PM EDT Tue Aug 15 2023

NCZ007>010-025-026-040-041-075>077-088-151930-
Lee NC-Chatham NC-Franklin NC-Vance NC-Durham NC-Harnett NC-
Person NC-Warren NC-Wake NC-Granville NC-Moore NC-Cumberland NC-
206 PM EDT Tue Aug 15 2023

...Thunderstorms will become more numerous and strengthen across
Moore, southeastern Person, Vance, Warren, Harnett, Granville, Lee,
Wake, Durham, Chatham and Franklin Counties through 330 PM EDT...

At 201 PM EDT, Doppler radar was tracking developing thunderstorms
in Granville, Vance, Wake and Lee Counties with the storms moving
northeast at 35 mph.

HAZARD...Winds in excess of 40 mph.

SOURCE...Radar indicated.

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

Locations impacted include...
Raleigh, Durham, Cary, Sanford, Henderson, Southern Pines, Oxford,
Creedmoor, Pittsboro and Louisburg.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

These storm will likely intensify, so be certain to monitor local
radio stations and available television stations for additional
information and possible warnings from the National Weather Service.

A Severe Thunderstorm Watch remains in effect until 900 PM EDT for
central North Carolina.

&&

LAT...LON 3654 7790 3630 7794 3582 7826 3571 7847
      3552 7871 3534 7853 3526 7860 3517 7912
      3521 7925 3504 7946 3507 7957 3551 7977
      3552 7955 3584 7954 3587 7901 3654 7880
TIME...MOT...LOC 1804Z 237DEG 30KT 3568 7884

MAX HAIL SIZE...0.00 IN
MAX WIND GUST...40 MPH

BLAES

Special Weather Statement
National Weather Service Raleigh NC
214 PM EDT Tue Aug 15 2023

NCZ021-022-038-151915-
Guilford NC-Forsyth NC-Davidson NC-
214 PM EDT Tue Aug 15 2023

...A strong thunderstorm will impact portions of Forsyth, northern
Davidson and western Guilford Counties through 315 PM EDT...

At 214 PM EDT, Doppler radar was tracking a strong thunderstorm near
Mocksville, moving northeast at 35 mph.

HAZARD...Winds in excess of 40 mph and pea size hail.

SOURCE...Radar indicated.

IMPACT...Gusty winds could knock down tree limbs and blow around
         unsecured objects. Minor damage to outdoor objects is
         possible.

Locations impacted include...
Greensboro, Winston-Salem, High Point, Lexington, Thomasville,
Kernersville, Clemmons, Bermuda Run, Huntsville and Lewisville.

This includes the following highways...
 Interstate 85 between Mile Markers 97 and 104.
 Interstate 40 between Mile Markers 182 and 216.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

This storm may intensify, so be certain to monitor local radio
stations and available television stations for additional information
and possible warnings from the National Weather Service.

A Severe Thunderstorm Watch remains in effect until 900 PM EDT for
central North Carolina.

&&

LAT...LON 3614 8044 3617 8044 3626 8025 3626 7999
      3606 7985 3592 7996 3592 8005 3581 8005
      3582 8047 3583 8049 3583 8043 3585 8038
      3589 8041 3589 8037 3596 8038 3599 8042
      3601 8042 3606 8046 3605 8051 3609 8052
TIME...MOT...LOC 1814Z 244DEG 29KT 3592 8064

MAX HAIL SIZE...0.25 IN
MAX WIND GUST...40 MPH

BLAES