Severe Thunderstorm Warning 219, NWS Raleigh, NC

Area Forecast Discussion
National Weather Service Raleigh NC
421 PM EDT Thu Sep 27 2018

.SYNOPSIS...
A cold front will drift into central NC today, then stall over the
region tonight through Friday. The front will resume a southeastward
trek friday night into Saturday as high pressure builds into the
region from the north.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 350 PM Thursday...

Convective activity beginning to increase in the southwest Piedmont
and and storms are exhibiting good mid-level rotation at this time
indicative of the better sheared environment in that area. Currently
about 1500 J/kg of ML CAPE are available to work with and about 25
kts of bulk shear. In the lowest level the 0-1 km shear is about 15
kts at this time with 0-1 km helicity values of 50-100 m2/s2. While
this is a decent environment for rotating storms, those low level
environment numbers are not particularly impressive and it is hard
to tell if this rotation will translate to the surface or remain
generally aloft. In general the afternoon is shaping up to have more
of the favored instability, but the best shear values remain well to
the northwest of the forecast area. These are expected to arrive
later, but by that time the instability could be lacking. Therefore,
it appears there is only a small window for the two to phase
together around 00z in the Triad.

At the surface, the cold front remains north of the forecast area
and this could remain the case for the duration of the afternoon and
evening. Later this afternoon a shortwave is expected to track
northeastward along or just ahead of the front and could provide
some extra forcing for ascent. Currently this feature appears to be
in western GA and will not arrive until after sunset. As a result
severe activity is expected to remain isolated to scattered through
the evening hours and focused north and west of US 1. With the front
staying to the north, lows this evening will remain in the mid 60s
to lower 70s.

&&

.SHORT TERM /FRIDAY AND FRIDAY NIGHT/...
As of 420 PM Thursday...

By Friday morning the front will still be lingering north of the
area but cloudy skies are expected to prevail through the day which
could keep temperatures down in the north but southern areas are
likely to break out in the afternoon causing temperatures to climb
once again into the mid to upper 80s. As the front sags slowly
southward, the US 64 corridor is likely to become convectively
active by afternoon. That being said, with less instability and
shear to work with, severe weather is not as likely as today and
therefore SPC has general thunder for the area. By Friday evening
this activity will push south and east as continental high pressure
moves in from the northwest. This may lead to a bit of an airmass
change across the northwest Piedmont by early Saturday morning with
lows in the low 60s but areas in the southeast still only bottoming
out near 70 degrees.

&&

.LONG TERM /SATURDAY THROUGH THURSDAY/...
As of 230 PM Thursday...

Saturday and Saturday night: Based on recent trends, would not be
surprise if the cold frontal passage Friday night/Saturday morning
is a bit slower than what models have been advertising. Given that
reasoning, could see some lingering shower activity over the
Sandhills and coastal plain counties Saturday morning, and possibly
even some isolated convective re-development during the afternoon,
in proximity to the deeper moisture axis and weak/moderate
instability gradient.

The delay in more notable sfc pressure rises from the north until
Saturday evening will result in highs Saturday very  similar to what
we see on Friday, although it should start to feel less humid across
the NW Piedmont with the arrival of lower dewpoints into the region.
Weak CAA overnight will bring slightly cooler and drier air into the
area Saturday night. Lows 60 to 65, with a few upper 50s possible in
the typically cooler spots across the northern Piedmont.

Sunday through Thursday: Subtropical ridge anchored across the
southeastern states will dominate through much of the upcoming week,
likely resulting in a  prolonged period of mostly dry conditions.
The EC hints at some weak shortwave disturbances circumventing the
western/northwestern periphery of the upper ridge, reasonably close
enough to possibly result in a few showers across the western and
northern portions of the piedmont by mid to late week. However,
until this becomes more evident, with leave forecast dry for now.

The near normal temperatures Sunday and Monday, courtesy of surface
high pressure nosing down the Mid-Atlantic Seaboard and resultant
NELY low-level flow will quickly moderate, allowing temperatures to
climb back into the lower to mid 80s, a good 5 to 8 degrees above
climatology, by mid to late week.

.AVIATION /18Z THURSDAY THROUGH TUESDAY/...
As of 215 PM Thursday...

MVFR ceilings holding on across much of the CWA this afternoon but
visible satellite imagery shows some chance for scattering out over
the next couple of hours, especially in southern and eastern
locations. After some earlier showers, radar is largely quiet at
this time but a few more robust cells with lightning starting to pop
up in the SW Piedmont.  This activity should become a little more
pronounced this afternoon but it could be closer to 00z before any
convection begins to threaten Triad TAF sites. This activity will
increase and move eastward through the overnight hours, likely
weakening as it does so. With the cold front still along the VA
border, all TAF sites have maintained a southerly flow at this time
but as the front slides southward, more variable wind directions can
be expected. Sub VFR clouds will likely hang on through the end of
the TAF period for northern terminal with southern returning to VFR
after sunrise on Friday.

Long Term: The front will linger over central NC presenting multiple
opportunities for adverse aviation conditions through Saturday
before the bulk of the activity will shift off to the southeast. A
likely return to VFR conditions for Sunday and into early next week.

&&

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

&&

SYNOPSIS...WSS
NEAR TERM...Ellis
SHORT TERM...Ellis
LONG TERM...CBL
AVIATION...Ellis

Hazardous Weather Outlook
National Weather Service Raleigh NC
429 PM EDT Thu Sep 27 2018

NCZ007>011-021>028-038>043-073>078-083>086-088-089-282030-
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-
429 PM EDT Thu Sep 27 2018

This Hazardous Weather Outlook is for central North Carolina.

.DAY ONE...Tonight.

A few strong to severe thunderstorms are possible late this
afternoon through this evening. The primary severe weather hazard
will be locally damaging wind gusts. An isolated tornado cannot be
ruled out. The severe weather threat appears to be highest between
8PM and midnight.

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

Hazardous weather is not expected at this time.

.SPOTTER INFORMATION STATEMENT...

Spotter activation may be needed.

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