Severe Thunderstorm Warning 255, NWS Raleigh, NC

AREA FORECAST DISCUSSION
National Weather Service Raleigh NC
402 PM EDT Wed Aug 10 2022

.SYNOPSIS...
High pressure centered off the Southeast coast will extend westward
across the Southeast states this afternoon. A cold front will
approach from the northwest tonight, then move slowly southeast
through North Carolina late Thursday through early Friday. A
secondary cold front will drop through the region late Friday. A
cooler and less humid air mass will build in from the north for the
weekend.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 301 PM Wednesday...

As expected, convection thus far has been strongest and most
widespread across the mountains. We are starting to see showers
develop across the northwest and southern Piedmont forced by
upstream outflow to the northwest, and a weak moisture gradient
associated with the sfc trough. Latest CAMs continue to suggest the
strongest forcing/convection will mostly stay north into central VA.
However, scattered to numerous showers and storms are still likely
to spread across the northwest tier of counties mid to late
afternoon before spreading/filling in east/northeast this evening,
and exiting/dissipating to the east by ~06Z tonight. Shear continues
to be weak this afternoon, but plenty of moisture, CAPE, and to some
degree DCAPE (~800 J/kg) is available for approaching storms to tap
into. Storms will therefore likely be pulse in nature, with perhaps
an isolated stronger downburst possible with any stronger/taller
storms. More concerning, however, is the potential for isolated
flash flooding through tonight. Given the high PWAT (>2 in)
available, and slow-moving nature to these storms, isolated flash
flooding will be possible primarily across the northern
Piedmont/Coastal Plain. According to the SPC mesoanalysis, a H9
moisture transport maxima is focused across our NE coinciding with
the highest PWAT and a weak vorticity maxima. CAMs have also
depicted a southerly surge of convection from VA through our NE
counties later tonight. As such, current thinking is heaviest rain
will fall in this vicinity which aligns with WPC's highest QPF over
our area. Any remaining showers/storms should push east of the
area/dissipate by ~06Z. Otherwise, another muggy night is expected
with lows in the lower to mid 70s.

&&

.SHORT TERM /THURSDAY AND THURSDAY NIGHT/...
As of 400 PM Wednesday...

A long-standing pattern since the end of July, one characterized by
a trough from the OH Valley to the lwr MS Valley and flanked by
ridges over the wrn N. Atlantic and Four Corners, will be in
transition this period. That trough and considerable moisture/
cloudiness above 700 mb, and likely to include at a least a few
small MCVs from convection extending this afternoon across the TN
Valley and srn Appalachians, will move from the w-cntl Carolinas and
TN Valley Thu morning to the coastal Carolinas Thu evening. While
those smaller MCVs may locally enhance ascent, synoptic height falls
related to the trough will be maximized over cntl NC early in the
day and prior to peak diurnal heating. Meanwhile, significant
longwave trough amplification will occur just upstream, from QC swwd
into the cntl Appalachians through 12Z Fri. Associated, seasonably
strong height falls (30-50 meters at 500 mb) will overspread cntl NC
late Thu night-early Fri.

In the low-levels, a synoptic front now over the Mid-Atlantic from
srn NJ, wwd across MD, and nrn WV, will have moved little by 12Z
Thu. It will move slowly southeast and across VA Thu afternoon and
evening and into cntl NC overnight Thu. A broad, pre-frontal trough
will precede the front and extend across NC through the day-evening.

Although cntl NC will remain in the warm sector that has supported
temperatures mostly in the 90s this month, the aforementioned
considerable multi-layer cloudiness will significantly hinder
insolation and diurnal destabilization. As such, high temperatures
are likely to be less hot/closer to average and range from mid 80s
across the nrn Piedmont to lwr 90s through the Sandhills and srn
Coastal Plain. This limited heating/destabilization, along with the
possibility for a period of subsidence during peak heating between
the two troughs noted above, casts uncertainty to the coverage of
showers and storms, which appear at this time to be less than
previously anticipated at least through the evening.

Whatever convection that does develop will likely linger or
redevelop through most of the night across the srn half of cntl NC,
where moisture and influence from the longwave trough and low level
frontal zone will remain maximized through the night. Meanwhile,
drier and more stable air characterized by temperatures and
dewpoints in the 60s, and partial clearing, will settle sewd and
into the nrn Piedmont by Fri morning.

&&

.LONG TERM /FRIDAY THROUGH WEDNESDAY/...
As of 330 PM Wednesday...

A second cold front will push southeast across the region Friday,
with areas south and east of the Triangle having the best chance of
a shower or thunderstorm through the evening. A shortwave trough
will also dig across the region through the day, helping to provide
better instability aloft. Cold air advection behind the front will
keep afternoon temps 5-10 degrees below normal for the northern half
of the region, while areas near the SC border will remain near or
slightly below normal. Dewpoints will still be in the mid to upper
60s, however areas near the VA border with the lower values will
have afternoon temps feeling more like the upper 70s.

Heights aloft remain low with continued northwesterly flow for the
weekend. Surface high pressure across the OH Valley on Saturday will
build south across the Blue Ridge on Sunday. Continued northerly
flow will transport a much drier airmass across the area, with
dewpoints in the 50s on Saturday. The high building to our south on
Sunday will switch winds to southerly, but only raise dewpoints
slightly to near 60 degrees. Highs in the low 80s N to upper 80s S
and low dewpoints will make it feel much nicer outside compared to
how it has been much of the summer. Highs only increase a few
degrees on Sunday. A shortwave digging across the region on Sunday
will create a small chance of showers and thunderstorms, mainly late
in the day/evening. EPS ensemble members are in good agreement on
this, however other ensembles are not as confident.

Early next week will become more active as a deep low dives south
towards the Mid-Atlantic and a few shortwaves round the low and move
across central NC. Additionally, a cold front will move southeast
across the region on Tuesday, creating additional possibilities of
precipitation. Dewpoints will increase back to the mid-60s through
the period, with highs remaining just above or just below normal.
Ensembles are looking more dry for Wednesday as surface high
pressure builds into the north behind the front.

&&

.AVIATION /18Z WEDNESDAY THROUGH MONDAY/...
As of 117 PM Wednesday...

Primarily VFR conditions are expected at all terminals through the
TAF period as the Bermuda high maintains control over the southeast.
However, brief periods of IFR/MVFR conditions and gusty downdrafts
will be possible this afternoon/tonight as convection spills off the
mountains and pushes eastward through central NC. Confidence is
highest at KINT/KGSO between ~21 to 00Z, and then KRDU/KRWI between
~23 to 04Z. Further south, confidence in timing precipitation is
lower, and thus only mention a few hours of VCTS in the KFAY TAF at
this update. Any remaining storms tonight should exit to the
east/dissipate by ~06Z. Some guidance depicts some fleeting MVFR
stratus near the Triad terminals near daybreak tomorrow, but
confidence is too low to include in the TAFs at this update.
Otherwise, expect light southwesterly flow (7 to 12 kts) to continue
this afternoon, diminishing some overnight, before picking back up
and turning a bit more westerly late tomorrow morning.

Outlook: VFR conditions are expected through mid to late morning
Thursday, but another round of showers/storms is expected to spread
northwest to southeast in the afternoon/evening as a cold front
pushes through our area. Consequently, brief periods of gusty
downdrafts and IFR/MVFR conditions will be possible Thursday. The
cold front will then settle across the NC/SC border Friday providing
continued support for scattered showers/storms primarily across the
south/east. High pressure builds into the area with dry and VFR
conditions expected late Friday through Sunday. The pattern quickly
returns to classic summertime afternoon showers/storms early next
week.

&&

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

&&

SYNOPSIS...Hartfield
NEAR TERM...Luchetti
SHORT TERM...MWS
LONG TERM...JJT
AVIATION...Luchetti

Hazardous Weather Outlook...UPDATED
National Weather Service Raleigh NC
637 AM EDT Wed Aug 10 2022

NCZ042-043-073>078-083>086-088-089-111045-
Johnston-Wilson-Stanly-Montgomery-Moore-Lee-Harnett-Wayne-Anson-
Richmond-Scotland-Hoke-Cumberland-Sampson-
637 AM EDT Wed Aug 10 2022

This Hazardous Weather Outlook is for central North Carolina.

.DAY ONE...Today and tonight.

No hazardous weather is expected at this time.

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

No hazardous weather is expected at this time.

.SPOTTER INFORMATION STATEMENT...

Spotter activation is not expected at this time.

NCZ007>011-021>028-038>041-111045-
Person-Granville-Vance-Warren-Halifax-Forsyth-Guilford-Alamance-
Orange-Durham-Franklin-Nash-Edgecombe-Davidson-Randolph-Chatham-Wake-
637 AM EDT Wed Aug 10 2022

This Hazardous Weather Outlook is for central North Carolina.

.DAY ONE...Today and tonight.

There is a marginal (level 1 out of 4) risk of excessive rainfall
this afternoon and evening across north central North Carolina.
Numerous showers and storms may produce localized torrential
rainfall, leading to areas of minor flooding, especially in urban
and poor drainage areas.

.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.

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