Severe Thunderstorm Warning 182, NWS Raleigh, NC

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

.SYNOPSIS...
A cold front will settle across the Carolinas through tonight, then
stall over the east-central Carolinas on Wednesday. High pressure
will build across the Tennessee Valley through Thursday.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 300 PM Tuesday...

Water vapor satellite showed an upper level low centered near the
Great Lakes region, with the associated trough swinging east across
the Blue Ridge. Surface obs showed a cold front moving southeast
across the NC foothills, and a hot and humid airmass ahead of the
front, with heat index values in the 100-115s across central NC,
away from the Triad. Radar displayed scattered thunderstorms
developing across the area. 0-6km shear of 30-40 kt and an unstable
airmass across the region is helping develop strong to severe storms
across the northern Piedmont, with sub-severe storms developing
elsewhere. As the front pushes closer to the area, additional storms
will likely develop and a large, broken line could develop along the
HWY-1 corridor as storms move into a more moist and hot airmass.
Although wind shear lowers across the Coastal Plain, downdraft CAPE
values up to 1500 J/kg will increase the threat of damaging wind
gusts from storms this afternoon and evening. A Severe Thunderstorm
Watch remains in effect across all of central NC through 9pm
tonight. Areas away from the Triad will remain dangerously hot, but
should see relief as rain falls this afternoon. A Heat Advisory and
Excessive Heat Warning remain in effect for portions of central NC
through 7pm this evening.

Conditions will improve from overnight, with light rain lingering
across portions of the southern Coastal Plain late tonight. Winds
will shift northwest after the front, with slightly drier air moving
in. Lows tonight will range from the mid-60s NW to mid-70s SE.

&&

.SHORT TERM /WEDNESDAY AND WEDNESDAY NIGHT/...
As of 245 PM Tuesday...

A shortwave trough centered over northern New England on Wednesday
morning will move NE into the Canadian Maritimes by the evening. A
second strong shortwave will dive into the Upper Midwest and Upper
Great Lakes on Wednesday/Wednesday night. Meanwhile weak longwave
troughing aloft will be centered to our west. At the surface, a cold
front that will pass through central NC tonight should reach near
the coast tomorrow morning, before it shifts back westward into
central NC in the afternoon and evening. Along and east of this
boundary, dew points will be in the lower-to-mid-70s. So there
should be sufficient MLCAPE (as much as 1000-1500 J/kg) and PW
values (1.5-2 inches, or near to slightly above normal) to result in
some isolated to scattered shower and storm development. Mid-level
heights don't fall during this period, so upper forcing will be weak
at best, and convective coverage is not expected to be widespread.
Shear will also be quite weak, as 500 mb flow will only be around 15
kts, which will greatly limit any severe threat. Looking at the 12z
HREF, the best chance of convection should be after 21z into perhaps
the early overnight hours, once the boundary is able to progress far
enough westward and a weak shortwave approaches the NC coast. The
best chance will be in the eastern Sandhills and central/southern
Coastal Plain, while it should be too dry and stable in NW zones for
any convection. With low-level thicknesses about 20-30 m lower than
today, high temperatures on Wednesday will be much more comfortable
and seasonable, in the mid-80s to around 90 (near normal), with lows
Wednesday night in the mid-60s to lower-70s.

&&

.LONG TERM /THURSDAY THROUGH TUESDAY/...
As of 400 PM Tuesday...

The strong shortwave will continue to push east across the Upper
Great Lakes and southern Ontario on Thursday and Thursday night, as
the longwave trough pushes east and become centered over our region.
Similar to Wednesday, 1000-2000 J/kg of CAPE will be possible across
southern and eastern zones, ahead of the stalled front. So scattered
showers and storms will be possible here, but shear again looks
weak, so the severe threat should be minimal. As the mid/upper
trough moves through and the flow aloft turns more westerly, drier
air will filter in which should help shut off convection fairly
quickly in the evening.

Models are then in good agreement on the weather pattern from Friday
into the weekend, showing the mid-level troughing finally lifting NE
into Canada and getting replaced by a ridge that will build over the
Plains and Southeast US. At the surface, another cold front will
move through central NC on Friday night, with high pressure building
down from the north before it moves offshore on Sunday. Thus expect
mainly dry conditions from Friday through Monday, with only slight
chance POPs in the far SE. Models start to differ on Monday night
and Tuesday, when the 12z GFS shows another shortwave trough
swinging through, and a minority of GEFS show precipitation. So
carry slight chance POPs in the south and east.

High temperatures will be slightly above normal on Thursday and
Friday (upper-80s to lower-90s), turning seasonable on Saturday
behind the cold front. A warming trend will then commence on Sunday
and Monday as the ridge builds east. Fortunately, dry air from high
pressure to our north should limit dew points to the 60s (maybe even
some 50s) from at least Friday into the weekend. So heat indices are
expected to stay below 100 through the period.

&&

.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 until 7 PM EDT this evening for NCZ010-024>026-040-
073>076-083-084.
Excessive Heat Warning until 7 PM EDT this evening for NCZ011-027-
028-041>043-077-078-085-086-088-089.

&&

SYNOPSIS...JJT
NEAR TERM...JJT
SHORT TERM...Danco
LONG TERM...Danco
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

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