Severe Thunderstorm Warning 167, NWS Raleigh, NC

AREA FORECAST DISCUSSION
National Weather Service Raleigh NC
340 PM EDT Thu Aug 1 2019

.SYNOPSIS...
A cold front will become nearly stationary across the central
Appalachians and middle Atlantic states through the weekend, keeping
afternoon/evening showers and thunderstorms in the forecast. The
upper-trough deepens a bit early next week, allowing numerous
impulses to pass through the region, elongating our active and wet
weather pattern.

&&

.NEAR TERM /TONIGHT/...
As of 140 PM Thursday...

Latest surface analysis depicts a quasi-stationary from draped
generally SW to NE along the spine of the Appalachians, with a
weakly defined lee-side trough positioned in similar orientation in
the vicinity of the US-1 corridor. Aloft, broad scale troughing
persists across the eastern CONUS, with a decaying shortwave
depicted well on GOES EAST water vapor imagery sliding east into the
Atlantic Ocean. In its wake, substantial clearing has commenced
across the eastern foothills and western Piedmont counties, allowing
modest destablization to occur.

As of 17z, mesoanalysis depicts broad scale SFC based CAPE values in
the 2500 - 3000 J/KG, ML CAPE approaching 2000 - 2500 J/KG, and
DCAPE values between 800 - 1000 J/KG across central NC. A bit more
capping in place today compared to yesterday, but it likely won't be
enough to inhibit storm initiation by mid to late afternoon,
especially with near 8*C/KM low-level lapse rates evident across
central NC. As a result, have backed initiation time off by an hour
or so, with initial cells likely going up across the eastern slopes
of the Blue Ridge Mountains before slowly propagating east into the
Triad region. Other possible initialization points include the
seabreeze front slowly progressing inland off the Atlantic, the
Piedmont/lee side trough from SW to NE, and any remnant outflow
boundaries from yesterday's ample convective coverage. With little
in the way of mid to upper-level support, not expecting much in the
way of organized convection this afternoon, however, a few strong
multicellular storms capable of producing heavy rainfall, sub-severe
hail, and isolated wind gusts will still be possible. The primary
threat, like yesterday, remains locally heavy rainfall which could
lead to pockets of flash flooding. With steering flow generally 15 -
20kts, cold pool propagation will be the primary drivers of
convection this evening, with some back building possible. Some low-
level boundary layer moistening has lead higher PWAT values (1.5 to
1.8 inches) and surface dewpoints, increasing the threat of locally
heavy rainfall with any slow moving storms that do form. Lastly,
with higher n-cape values this evening, the lightning in the storms
may also be a bit more robust. Storm coverage decreases during the
overnight hours.

Temperatures are still on track to top out in the upper 80s
(northwest) to lower 90s across central NC. Overnight, mid to upper-
level clouds will remain a bit more dense, with some low-level
stratus and fog possible. Overnight lows will bottom out in the
upper 60s to lower 70s.

&&

.SHORT TERM /FRIDAY THROUGH FRIDAY NIGHT/...
As of 240 PM Thursday...

Central NC will remain in the action zone situated between the broad
scale upper trough draped across the eastern CONUS and the Bermuda
high off the Atlantic Coast. This will continue the gradual surface
warming and moistening trend across central NC, helping to inch up
surface dewpoints, especially along and east of US-1. This will help
to enhance our shower thunderstorm coverage on Friday afternoon,
even with a bit more overhead cloud cover in play attempting to
limit the diurnal destabilization processes. Even so, scattered
shower and thunderstorms are expected to form across central NC,
primarily along any leftover differential heating/outflow boundaries
related to Thursday's convection, along with additional scattered
formation in terrain/sea breeze favored areas. Primary threat
remains the possibility of excessive rainfall which could lead to
pockets of flash flooding, with an isolated severe wind gust threat.
Temperatures are progged to be 4 to 8 degrees cooler on Friday, in
the low to mid 80s, thanks to the persistent overhead cloud deck.
Overnight lows will remain seasonable, bottoming out in the upper
60s to low 70s.

&&

.LONG TERM /SATURDAY THROUGH WEDNESDAY/...
As of 340 PM Thursday...

Shortwave impulses emanating through the upper trough will continue
to interact with the deep moisture(PWATS 1.75-2.0") and instability
in place to bring a good chance of convection each day through
Monday. Given the high likelihood that some these upper disturbances
will be convectively enhanced/augmented, so it's nearly impossible
to get overly specific with timing and location of highest PoPs.
Thus, will continue to advertise diurnally favored PoPs, while
maintaining a slight to small chances overnight. Vertical wind shear
is forecast to be rather weak. Thus, any severe weather should be
largely unorganized(pulse severe) with the primary threat being
locally heavy rain and flash flooding.

Could see a brief reprieve in the wet and unsettled conditions
Tuesday and Wednesday as the axis of deeper moisture slides east and
out to sea. However, a reinforcing trough from the west could bring
another wet and unsettled pattern to end the week.

Lows in the upper 60s to lower 70s. Highs in the lower to mid 80s NW
to upper 80s/lower 90s SE.

&&

.AVIATION /17Z THURSDAY THROUGH MONDAY/...
As of 1240 PM Thursday...

VFR conditions continue across all of the central NC terminals this
morning, and should persist through the majority of the period
through this evening. The one temporary exception would be related
to possible shower and thunderstorm development this afternoon and
evening, which will likely cause at least temporary drops in
category due to heavy rainfall rates decreasing CIGs/VSBYs values.
With generally airmass type thunderstorms anticipated, have trended
with including VCTS at all TAF sites, relying on tempo groups to
showcase time of most likely occurrence. In general, best thunder
chances will be between 20z/4pm and 23z/7pm this evening, but
isolated showers and storms could persist into the overnight hours.
Some at least isolated fog/stratus formation will be possible again
pre-dawn Friday, but highly dependent on how the storm activity
takes shape later on today. For now, have left mention of VFR
CIGs/VSBYs in at KINT/KGSO/KRWI between 09z/5am - 13z/9am with some
lingers sub-VFR CIGs possible at the Triad Terminals. Conditions
should slowly improve by mid morning, but confidence here remains
low.

Looking beyond 18z Friday, the stormy pattern should continue well
into next week. This will leave us in a daily pattern of early-
morning sub-VFR fog/stratus, along with high shower/storm chances
each afternoon and evening at minimum.

&&

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

&&

SYNOPSIS...JJM
NEAR TERM...JJM
SHORT TERM...JJM
LONG TERM...CBL
AVIATION...JJM

Hazardous Weather Outlook
National Weather Service Raleigh NC
249 PM EDT Thu Aug 1 2019

NCZ007>011-021>028-038>043-073>078-083>086-088-089-021900-
Person-Granville-Vance-Warren-Halifax-Forsyth-Guilford-Alamance-
Orange-Durham-Franklin-Nash-Edgecombe-Davidson-Randolph-Chatham-Wake-
Johnston-Wilson-Stanly-Montgomery-Moore-Lee-Harnett-Wayne-Anson-
Richmond-Scotland-Hoke-Cumberland-Sampson-
249 PM EDT Thu Aug 1 2019

This Hazardous Weather Outlook is for central North Carolina.

.DAY ONE...This afternoon and tonight.

Scattered to numerous thunderstorms featuring frequent lightning,
localized damaging wind gusts, and locally heavy rain are expected
over central North Carolina this afternoon and evening. Heavy
rainfall rates within the slower moving storms could lead to urban
and small stream flooding along with pockets of flash flooding
possible.

.DAYS TWO THROUGH SEVEN...Friday through Wednesday.

Scattered to numerous thunderstorms are expected to persist through
Monday, mainly during the afternoon and evening hours. Locally heavy
rain, isolated damaging wind gusts, and frequent lightning will be
the primary hazards with the strongest storms.

.SPOTTER INFORMATION STATEMENT...

Spotter activation may be needed.

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