Special Weather Statement, NWS Raleigh, NC

Area Forecast Discussion
National Weather Service Raleigh NC
752 PM EDT Wed Aug 1 2018

.SYNOPSIS...
A wet and humid atmosphere combined with a series of disturbances
passing overhead will maintain clusters of showers and thunderstorms
with heavy rain across central NC through the rest of the work week.

&&

.NEAR TERM /THROUGH THURSDAY/...
As of 330 PM Wednesday...

Showers and thunderstorms have continued to develop this
afternoon and pivot west with the best upper level diffluence.
Best MLCAPE values remain along the coastal plain this afternoon
(around ~2000 J/kg) with slightly lower values through central
NC. DCAPE values are mostly less than 1000 J/kg, but SFC to 6km
bulk shear remains around 40 kts. Mid-level dry air also can be
seen nudging in from the east with forecast soundings showing
sfc-delta theta e values approaching -30 in places. Due to this
some gusty winds will be possible in any stronger storms. The
storms are forecast to continue to focus more towards the west
this evening along with the LLJ convergence. Overall, rainfall
totals are not expected to be as high as some of the more potent
storms Tuesday night, but isolated rainfall totals of 1 to 2"
are possible. This is mainly due to the increased flow with SFC
to 6 km mean wind now up to 30 kts.

Late this evening, convection will decrease in coverage until
another shortwave rounds the base of the subtropical ridge. The
overall setup is for the rex block to slowly break loose over
the western Atlantic with a retrograding low pressure
approaching the area from the east. A potent upper level trough
axis will also remain across the central United States. PWATs
also remain elevated (above 2.00") or near max values for this
time of year. Due to the above, widespread showers and
thunderstorms can be expected Thursday. The main question for
Thursday will be the potential for heavy rain. As of right now
the best upper level support and shortwave energy appears to be
just west of the CWA, but warm cloud depth layers are around
12.5kft and PWATs are also near max values. Flash flood guidance
has also come down across the western counties. The latest QPF
means from the GEFS and EPS are just below guidance so will hold
for now. A flash flood watch might be needed for the western
counties Thursday. This will need to be watched.

Thursday evening into Friday the chance of rain looks to
continue as upper level support and high moisture values
continue across the region.

&&

.SHORT TERM /FRIDAY AND FRIDAY NIGHT/...
As of 115 PM Wednesday...

It appears that Friday will be the last in this series of very wet
days with a threat of flash flooding. Scattered to numerous showers
and thunderstorms are expected, especially in the afternoon and
evening hours.

The anomalous trough over the eastern United States is forecast
to finally begin to lift out as a strong western Atlantic ridge
surges westward toward eastern NC. As the trough lifts out and
weakens the main forcing will also lift up into the northern Mid-
Atlantic states Friday. The residual deep moisture is still forecast
to be over the region along with a weak low level boundary for a low
level focus. With surface heating Friday, expect that there will be
a strong uptick in showers and storms again. With slower storm
motion by that time and areas of saturated grounds, a flash flood
risk should continue through Friday evening. Picking out "favored"
areas for a higher risk are too difficult at this time given the
localized nature of convection. Highs Friday should again be
tempered by the moisture, clouds, and showers with mostly 80s
anticipated. Lows Friday night 68-74.

&&

.LONG TERM /SATURDAY THROUGH WEDNESDAY/...
As of 110 PM Wednesday...

The aforementioned subtropical ridge is expected to build westward
and over the SE states this weekend into Monday. Then, another
trough is expected to develop over the upper Midwest again, then
shift into the eastern United States mid to late week.

Even though there will be drier aloft, plentiful low level moisture
and strong heating will combine with the more typical Appalachian
lee surface trough to produce at least a daily 30-40 percent chance
of thunderstorms, mainly in the afternoon and evening hours each
day. The chances of thunderstorms should increase again as the new
trough begins an approach mid week. Lows in the 70-75. Highs 88-94.

&&

.AVIATION /00Z THURSDAY THROUGH TUESDAY/...
As of 750 PM Wednesday...

24 hour TAF period: Showers and thunderstorms will continue over
KINT and KGSO for the next couple of hours, accompanied by visbys of
1 SM or less, cigs in the 2-4 kft range and gusty winds of 25-40
kts. A shower and isolated thunderstorm is possible in the next
couple of hours at KFAY, with some reduced cigs and visbys and
breezy conditions also possible there. It's possible KRDU and KRWI
could be rain/thunder free through the overnight, but should the
showers to the south hold together or new ones develop then there
will be a chance at those terminals as well. Although spotty showers
will be possible overnight for points east of the Triad (where
showers are most likely) chances are too low at this time and will
be an "update as it comes" forecast. With the rainfall from today
and little change in airmass from last night, expect redevelopment
of sub-vfr cigs overnight and into daybreak Thursday. Expect
additional showers and thunderstorms on Thursday afternoon/evening,
becoming more numerous and widespread beyond 18Z or so, with the
same accompanying conditions as listed above where they occur. -KC

Looking ahead: Numerous showers and thunderstorms will continue
Thursday evening. In any of the stronger storms, vsby restrictions
and gusty winds will occur. This pattern will continue through
Saturday with morning MVFR to IFR conditions and scattered to
numerous afternoon showers and thunderstorms. By Sunday into Monday
a mid-level ridge will build overhead meaning less coverage of
showers and thunderstorms and improved aviation conditions. -BH/KC

&&

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

&&

SYNOPSIS...Haines
NEAR TERM...Haines
SHORT TERM...Badgett
LONG TERM...Badgett
AVIATION...KC/Haines

Hazardous Weather Outlook
National Weather Service Raleigh NC
314 PM EDT Wed Aug 1 2018

NCZ007>011-021>028-038>043-073>078-083>086-088-089-021915-
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-
314 PM EDT Wed Aug 1 2018

This Hazardous Weather Outlook is for central North Carolina.

.DAY ONE...This Afternoon and Tonight.

Pockets of locally heavy rainfall are possible through tonight,
which may produce localized street flooding in areas of poor
drainage. In addition, some stronger storms could produce isolated
damaging wind gusts.

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

There is a chance for locally heavy rainfall Thursday into Friday.

.SPOTTER INFORMATION STATEMENT...

Spotter activation is not expected at this time.