Special Weather Statement, NWS Raleigh, NC

Area Forecast Discussion
National Weather Service Raleigh NC
220 PM EDT Sat Mar 18 2017

.SYNOPSIS...
A cold front will cross the region this evening. High pressure will
build into the Carolinas from the west for the remainder of the
weekend.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 215 PM SATURDAY...

Light rain assoc/w low-level warm advection and small amplitude
waves in westerly flow aloft has progressed east of the I-95
corridor as of 18Z. Aside from cirrus, skies have already cleared in
the Western Piedmont, where temps have rebounded into the lower 60s.
East of Hwy 1, temps remained in the upper 40s to lower 50s. Expect
afternoon highs to range from the mid 60s in the far Western
Piedmont to the mid/upper 50s in the Coastal Plain, coolest east of
I-95 where light rain and low ceilings will erode the latest.

A ~110 knot jet streak diving SSE through the OH valley this morning
(on the western periphery of an upper level low over the lower Great
Lakes) will amplify an upper level trough over the region as it digs
into the western Carolinas today. As a result, strong height falls,
strengthening cyclonic shear/curvature vorticity and increasingly
diffluent flow aloft (in the left exit region of the PJ) will be
favorably juxtaposed with a cold front /low-level trough/
progressing east across central NC. Although FROPA will occur a few
hours after peak heating, rapid destabilization is expected along
the front as it progresses into a thermodynamic environment
characterized by decreasing Theta-E w/height in the presence of
strong upper forcing /layer-lifting/, particularly in vicinity of
the Hwy 1 corridor. NAM forecast soundings show marked cooling aloft
(-10C isotherm falling to 11 KFT and -20C isotherm falling to 16
KFT) and rapid steepening of low/mid-level lapse rates late this
afternoon, with as much as 500-1000 J/kg of MLCAPE and SCP values as
high as 3-5 by ~00Z at RDU (similar parameters at RWI). The 12Z
NAM4KM and a number of HRRR model runs suggest that, after the lull
this afternoon, scattered convection will re-develop along the front
in central VA/NC in the 21-00Z time frame, progressing east of the I-
95 corridor by Midnight. In the wake of the front, winds will veer
to the W/WNW and increase to 10-15 kt with gusts up to 25 kt this
evening, though gustiness may decrease and become sporadic after
midnight if a shallow nocturnal inversion develops despite CAA.
Overnight lows will be driven by cold advection, in the mid/upper
30s, coldest NW Piedmont.

Severe Potential: A conditional potential for isolated supercells
capable of producing quarter to golfball size hail and damaging
winds will exist late this afternoon and evening, particularly
along/east of Hwy 1 and north of Hwy 64, or from the Triangle north
and northeast to the VA border between ~21Z this afternoon and ~03Z
this evening. -Vincent

&&

.SHORT TERM /SUNDAY AND SUNDAY NIGHT/...
As of 135 PM SATURDAY...

Patchy frost or a light freeze is possible Sunday night across the
northern tier counties...

The upper low will be in the vicinity of Tidewater VA Sunday
morning, having moved rapidly south southeast overnight. Model time
sections show a surge of deeper moisture and potential for some
showers accompanying the upper low, and this surge will graze our NE
counties between 12 and 16 UTC. The cloud coverage and stronger cold
air advection will also be slanted in that direction, resulting in a
slower warmup with highs in the northeast stalling in the mid 50s,
while upper 50s are expected elsewhere under mostly sunny skies.
Northerly winds will gust to 20 mph, with gusts up to 25 mph along
and east of I95.

The pressure gradient will weaken rapidly Sunday night as high
pressure builds quickly over the region, allowing winds to diminish
to light and variable after sunset. Good radiational conditions will
allow mins to fall to the low to mid 30s by sunrise Monday - which
is about 10 degrees below normal.

&&

.LONG TERM /MONDAY THROUGH SATURDAY/...
As of 135 PM Saturday...

Surface high pressure will quickly slip south of the area on Monday,
with winds backing to southwest and setting up a warming trend
Monday into Tuesday with highs Monday climbing to the mid 60s, and
further into the low and mid 70s Tuesday. Tuesday will be a
transition day despite the warm temperatures, however, as a cold
front will be developing across the Ohio Valley and sinking slowly
south into the area by Tuesday afternoon, accompanied by widespread
showers and possibly some thunderstorms which will persist through
Tuesday night as the front slowly edges south.

The showers will be diminishing and should be ending across the
southern tier counties by mid day Wednesday. Clearing will be rather
slow, and may be delayed until Wednesday night, and the ensuing cold
air advection will limit highs on Wednesday to the mid and upper
50s. The cool air mass settling down the Atlantic seaboard will push
mins to the low and mid 30s Wednesday night, and highs Thursday will
struggle to reach 50-55.

The warming cycle begins anew on Friday as the high pressure moves
offshore and southerly return flow begins raising our thicknesses
and moisture levels ahead of our next cold front, tentatively
scheduled to race across central NC on Saturday. Highs Friday will
reach low to mid 60s, and further to the mid and upper 60s Saturday.
We will see at least modest shower coverage in the prefrontal
airmass early Saturday and probably a respectable line of convection
accompanying the front later in the day.

&&

.AVIATION /18Z SATURDAY THROUGH THURSDAY/...
As of 130 PM SATURDAY...

24-HR Taf Period: Lingering MVFR visbys assoc/w light rain will
affect the RWI terminal through ~19Z. Otherwise, expect VFR
conditions with ceilings AOA 5 KFT through at least 21Z. Between 21-
03Z, sct showers/storms are expected to develop along a cold front
progressing through central NC. Any terminal could be affected for a
few hours late this aft/eve, though RDU/FAY/RWI are more likely to
experience convection than INT/GSO, including a potential for isold
severe storms capable of producing sfc wind gusts of 35-50 knots and
quarter to golfball size hail. VFR conditions are expected
everywhere by ~Midnight in the wake of the cold frontal passage.
SSW/SW winds at 5-10 knots this afternoon will veer to the WNW at 10-
15 knots with gusts up to 25 knots in the wake of the front this
evening. Breezy WNW winds will persist overnight, becoming northerly
at 10-15 kt with gusts to 20-25 kt by mid/late Sunday morning.

Looking Ahead: VFR conditions will rule Sun/Mon as high pressure
builds over the region in the wake of the front. Sub-VFR conditions
are expected to return Tue/Tue night in assoc/w low ceilings and
rain along/behind a backdoor cold front moving southward through the
region. VFR conditions will return Wed/Thu as strong Mid-Atlantic
high pressure extends southward through the Carolinas. -Vincent

&&

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

&&

SYNOPSIS...Vincent
NEAR TERM...Vincent
SHORT TERM...mlm
LONG TERM...mlm
AVIATION...Vincent

Hazardous Weather Outlook...UPDATED
National Weather Service Raleigh NC
341 PM EDT Sat Mar 18 2017

NCZ007>011-021>028-038>043-073>078-083>086-088-089-191945-
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-
341 PM EDT Sat Mar 18 2017

This Hazardous Weather Outlook is for central North Carolina.

.DAY ONE...This Afternoon and Tonight.

A potent upper level disturbance will dig southeast into the
region late this afternoon and evening as a cold front tracks east
across the Carolinas. Scattered showers and thunderstorms will
develop along and ahead of the front. A few storms could become
severe, with a primary threat of quarter size hail and damaging
winds.

.DAYS TWO THROUGH SEVEN...Sunday through Friday.

Hazardous weather is not expected at this time.

.SPOTTER INFORMATION STATEMENT...

Spotter activation is not expected at this time.

Vincent

Special Weather Statement
National Weather Service Raleigh NC
346 PM EDT SAT MAR 18 2017

NCZ083-084-182030-
Richmond NC-Anson NC-
346 PM EDT SAT MAR 18 2017

 ...A strong thunderstorm WILL AFFECT PORTIONS OF Richmond and
southern Anson Counties Until 430 PM EDT...

At 344 PM EDT, Doppler radar was tracking A strong thunderstorm near
Wadesboro, moving east at 40 mph.

Pea size hail and wind gusts up to 45 mph will be possible with this
storm.

Locations impacted include...
Rockingham, Wadesboro, Hamlet, Hoffman, Polkton, Ellerbe, Dobbins
Heights, Lilesville, Morven and McFarlan.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Seek shelter in a nearby building or vehicle. Wind gusts as high as
40 mph are capable of knocking down tree limbs and blowing around
trash cans, potted plants, lawn furniture and other light outdoor
objects.

&&

LAT...LON 3510 7958 3508 7958 3507 7957 3506 7950
      3504 7946 3499 7957 3494 7959 3491 7956
      3485 7963 3482 7962 3482 7963 3480 7969
      3481 8006 3483 8023 3501 8024
TIME...MOT...LOC 1944Z 271DEG 36KT 3492 8013

22

Special Weather Statement
National Weather Service Raleigh NC
405 PM EDT SAT MAR 18 2017

NCZ083>085-182045-
Scotland NC-Richmond NC-Anson NC-
405 PM EDT SAT MAR 18 2017

...A cluster of strong thunderstorms will affect portions of
Scotland... southeastern Richmond and southeastern Anson Counties
Until 445 PM EDT...

At 404 PM EDT, Doppler radar was tracking a cluster of strong
thunderstorms near Wadesboro, moving east at 45 mph.

Pea size hail and wind gusts up to 45 mph will be possible with this
storm.

Locations impacted include...
Laurinburg, Rockingham, Wadesboro, Hamlet, Hoffman, Dobbins Heights,
Gibson, Lilesville, Morven and East Laurinburg.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Seek shelter in a nearby building or vehicle. Wind gusts as high as
40 mph are capable of knocking down tree limbs and blowing around
trash cans, potted plants, lawn furniture and other light outdoor
objects.

&&

LAT...LON 3469 7954 3480 7968 3481 8004 3482 8009
      3500 8009 3505 7946 3500 7941 3467 7944
TIME...MOT...LOC 2004Z 271DEG 41KT 3491 8000

22