Severe Thunderstorm Warning 109, NWS Raleigh, NC

Area Forecast Discussion
National Weather Service Raleigh NC
255 PM EDT Fri Jul 6 2018

.SYNOPSIS...
An Appalachian-lee surface trough will drift southeastward across NC
and VA this afternoon and evening, followed by the passage of a cold
front overnight. High pressure will then build across the middle
Atlantic region through the weekend, bringing much cooler and drier
air to our region.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 255 PM Friday...

A fairly large cluster of thunderstorms has developed/spread SE off
the Blue Ridge of VA/NC early afternoon. A cold pool in behind the
cluster of storms (temperatures in the 60s to lower 70s) has spread
out of the high country into the Foothills. Out ahead of the storms,
the MLCapes have reached 1500 to 2000 J/KG. There are cell mergers
going on with the storms propagating SSW. It appears that a short
lived pulse severe event is unfolding over the Triad region, with
the threat of a few damaging wind gusts to 60 mph.

The energy from this convection is expected to link up with the
scattered storms developing over the Piedmont during the mid to late
afternoon. This will enhance the convection along the I-40/I-85
corridors from the Triad to the Triangle spreading SE through the
afternoon. Generally, a few pulse severe may continue to be a threat
through the afternoon. Not sure the models have captured the cold
pool moving into the high CAPE environment very well.

The 12z/GFS was out to breakfast (lunch) as it had no storms in the
Triad until 00z/this evening. So, this can't be used. Going to the
CAMS, the HRRR may have the best handle on this situation - with the
energy of the cluster of storms and trailing cold pool will
translate SSE across our region through the afternoon and early
evening. The slow movement, cell mergers, and back building nature of
the storms as they come SE should continue to produce locally
damaging wind, frequent lightning, and very heavy rain.

High PW and slow storm motion will lead to locally heavy rain in the
storms. However, FFG is high as many areas have not seen rain in
over a week. Many areas are showing a very dry top moisture profile
as well. Therefore, the flash flood risk is low. Urban areas run the
risk any time of slow moving, heavy rain producing storms. However,
widespread flooding is not expected.

Severe storms on an organized basis are not expected due to the weak
shear. However, in this multi-cell pulse environment characterized
by high CAPE and nil shear, isolated strong wind events can and will
occur under the stronger cells.

The chance to likely POP will not drop off until later this evening,
with CAMS suggesting the focus for additional storms near the cold
front over NW NC this evening. The current convective overturning in
the NW may hamper additional strong storms later. There is a chance
of additional storms with the front as it drops south through the
region just about anywhere overnight. Lows in the upper 60s north to
lower to mid 70s south.

&&

.SHORT TERM /SATURDAY AND SATURDAY NIGHT/...
As of 130 PM Friday...

Surface cold front will be draped across southern NC on Saturday.
Meanwhile, a mid level ridge will redevelop and strengthen across
the upper Midwest into the Ohio Valley early this weekend. Beneath
the developing ridge, a Canadian surface high will build from the
Great Lakes east across the middle Atlantic states, and then
southward down the lee of the Appalachians. The cooler and drier
air, characterized by dewpoints in the upr 50s-mid 60s, will surge
into central NC Saturday into Saturday night. Expect a stubborn
extensive layer of stratocumulus layer over most of the area north
of the cold front. Scattered, mainly elevated, showers are expected,
with higher chances in the south.

Temperatures will be considerably cooler beneath the cloudiness and
aided by northeasterly flow that will gust to 20 or so mph on
Saturday. Highs are expected to be in the upper 70s north to very
low 80s across the southern tier. It will be pleasantly cool
Saturday night, with lows mostly in the low and mid 60s.

&&

.LONG TERM /SUNDAY THROUGH SATURDAY/...
As of 115 PM Friday...

The long term forecast will be subject to some uncertainty in the
Coastal Plain, as a low pressure area currently a few hundred miles
southeast of the NC coast may strengthen to a tropical depression as
it slowly approaches the coast later this weekend.

Otherwise, an initially 'cool' and dry continental airmass will make
a brief southerly surge down the Atlantic coast this weekend. The
ridging will retrograde across the Ohio Valley Monday as the airmass
quickly begins to modify with temperatures rising from low and mid
80s Sunday to the upper 80s Monday, and finally back to the lower
90s Tuesday.

The ridging will begin to amplify in the Plains Monday, with
subsequent troffing and northwest flow over the eastern CONUS. We
will continue to warm through midweek, with highs Wednesday through
Friday reaching the mid 90s. A backdoor front will be pushed south
into the area as the pattern amplifies on Thursday, and this front
will merge into our near-omnipresent summer lee trof and stall over
the area through the late week. This will enhance our chance of
convection Thursday and Friday.

&&

.AVIATION /18Z FRIDAY THROUGH TUESDAY/...
As of 245 PM Friday...

Pulse type storms will be a threat for the TAF sites through
00z/Saturday, transitioning to the SE zones between 00z and 03z.
There is another chance of storms in the Piedmont as the actual
front moves in later this evening and overnight. MVFR to IFR CIGS
and VSBYS will accompany the storms, then generally VFR conditions
later this evening. As the front moves through later tonight, the
winds will shift to the NE and pick up to 10-20kt between 06z and
12z, with a low IFR overcast expected.

The overcast should lift to MVFR Saturday afternoon, otherwise
generally VFR conditions expected.

Outlook: VFR conditions as drier high pressure builds more fully swd
across NC by Saturday night and Sunday, lasting into early next
week.

&&

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

&&

SYNOPSIS...Badgett/MWS
NEAR TERM...Badgett
SHORT TERM...mlm
LONG TERM...mlm
AVIATION...Badgett

Hazardous Weather Outlook
National Weather Service Raleigh NC
1147 AM EDT Fri Jul 6 2018

NCZ007>011-021>028-038>043-073>078-083>086-088-089-071600-
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-
1147 AM EDT Fri Jul 6 2018

This Hazardous Weather Outlook is for central North Carolina.

.DAY ONE...This Afternoon and Tonight.

Hot and humid conditions will exist out ahead of a cold front this
afternoon. Heat indices around 100 can be expected in many areas
before the chance of thunderstorms and clouds increase this
afternoon.

Clusters of thunderstorms will occur this afternoon and
evening. Some of the thunderstorms will produce locally heavy rain,
frequent lightning, and gusty wind to 50 mph. Some urban or small
stream flooding may occur. Thunderstorms are expected to diminish by
late evening.

.DAYS TWO THROUGH SEVEN...Saturday through Thursday.

No hazardous weather is expected at this time.

.SPOTTER INFORMATION STATEMENT...

Spotters are encouraged to report heavy rain amounts, strong winds,
or hail to the National Weather Service.

Badgett

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