Severe Thunderstorm Warning 159, NWS Raleigh, NC

Area Forecast Discussion
National Weather Service Raleigh NC
350 PM EDT Mon Aug 7 2023

.SYNOPSIS...
A cold front and upper level trough will approach from the west
bringing increased chances for strong to severe thunderstorms
through this evening. The cold front will move through the area
tonight and early Tuesday, followed by weak high pressure from late
Tuesday through Wednesday. Another system should affect the region
Thursday from the west.

&&

.NEAR TERM /TONIGHT/...
As of 350 PM Monday...

The slow demise of morning cloud cover has kept temperatures down
this afternoon across the northern Piedmont counties with heat
indices currently running in the upper 80s to mid 90s. Meanwhile the
leading edge of the convective cloud debris from approaching storms
is starting to spread into the area, which will further hold temps
down. Thus, the Heat Advisory has been cancelled. Elsewhere across
the advisory area(southern and eastern NC), heat indices of 100 to
105 is expected through remainder of the afternoon.

Previous Discussion:

- Tornado Watch in effect through 9 PM this evening for the Triad
region.  Additional convective watches may be needed farther east
later today.

The stage still appears to be set for a notable severe weather
episode across central NC later this afternoon as the squall line
currently moving across eastern TN spreads eastward and eventually
moves across our area between 21Z and 02Z this evening.  All of this
activity associated with a short wave trough moving across the Ohio
Valley and a mid-level and upper-level jet streak lifting E and NE
around the base and eastern side of the trough.

The main challenge so far today has been the pesky low clouds over
the Piedmont that have been slow to erode.  These clouds have held
sfc temps back so far, but now that they are finally eroding, we're
seeing temps climbing through the 80s across the Piedmont.  Areas
east of I-95 have had no problem climbing into the 90s with HI
values currently approaching 100 in many spots, yet still a couple
degrees shy of heat index criteria.

The challenge for the rest of this afternoon will be determining to
what extent the aforementioned low clouds may inhibit CAPE as the
storms cross the mountains and head toward our CWA. Despite the
slightly cooler temps than original expected, the overall forcing
for ascent associated with the potent short wave trough, coupled
with the increasing bulk shear which is expected to increase to 35-
40kt over our area by the time the storm arrive, should be enough to
overcome any local minimums in instability to result in scattered to
numerous damaging thunderstorms with the primary hazard being
damaging wind gusts, but isold tornadoes and hail can't be ruled out
either.  A tornado watch is in effect through 9 PM this evening for
the Triad region.  Additional convective watches may be needed
farther east later today.

Storms are expected to exit our CWA to our east before midnight with
some patches of stratus and/or fog developing before sunrise, but
this will likely depend on where the heaviest rain falls later
today. Lows tonight from the upper 60s NW to mid 70s SE.

&&

.SHORT TERM /TUESDAY THROUGH TUESDAY NIGHT/...
As of 300 PM MONDAY...

In the wake of Mondays shortwave, the surface cold front will move
across the  region dry, filtering in slightly cooler temps with
highs in the mid to upper 80s NW to low/mid 90s SE. Westerly winds
during the day will be 5 to 10 kts before veering to a light
north/northwesterly Tuesday night.

&&

.LONG TERM /WEDNESDAY THROUGH MONDAY/...
As of 342 PM Monday...

Wednesday will have dry conditions as high pressure influences the
Mid-Atlantic. Highs will generally be copy and paste for the latter
half of the week with highs in the upper 80s to low 90s NW to
low/mid 90s SE. Another shortwave is expected to move into the
region Thursday and Friday bringing the next chance of showers and
storms. For now, slight chance PoPs beginning Thursday morning then
higher PoPs in the afternoon and through the evening. As the trough
moves slightly east early Friday expect dry conditions during the
day with an isolated afternoon shower/ storm possible in the
southern portions of the CWA ( Triangle and south). Over the
weekend, a weak Piedmont trough is expected to linger across the
region influencing late afternoon showers and storms each day into
early next week.  With temps in the low to mid 90s combined with dew
points in the upper 70s, some areas in the south and east portions
of the CWA will experience heat indices above of 100 to 107 degrees.
&&

.AVIATION /18Z MONDAY THROUGH SATURDAY/...
As of 114 PM Monday...

Through 18Z Tuesday:  The stratocu across central NC has been slow
to lift so far today and we're still seeing MVFR cigs from RDU
westward to the Triad and south to KVUJ.  VFR conditions are found
along and east of I-95.  Satellite trends suggest slow thinning of
said clouds with a brief period of VFR before clouds increase again
associated with anticipated convection and line of shower/tstms that
are expected to move from west to east across central NC between 21Z
this afternoon and 02Z this evening.  Flt conditions will drop to
IFR with local variable wind gusts up to 50kt possible in and near
tstm activity.  Flt conditions will improve overnight tonight after
02Z after the storms move east of central NC.  A few patches of sub-
VFR fog and/or stratus can't be ruled out between 09-12Z Tuesday,
but that will depend on where the heaviest rain falls, so for now
have left this out of the TAFs.

After 18Z Tuesday:  VFR conditions expected through much of the
extended period with mainly dry conditions expected Tuesday and
Wednesday.  The risk for isold afternoon/evening tstms will return
on Thursday.

&&

.RAH WATCHES/WARNINGS/ADVISORIES...
Heat Advisory until 7 PM EDT this evening for NCZ010-011-027-028-042-
043-073>078-083>086-088-089.

&&

SYNOPSIS...np
NEAR TERM...CBL/np
SHORT TERM...CA
LONG TERM...CA
AVIATION...np

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