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Day 1 Outlook Convective Tornado
Hail Wind
Categorical Day1 1300Z Outlook
  
Images courtesy of the NWS Storm Prediction Center
 Forecast Discussion

  
000
ACUS01 KWNS 151257
SWODY1
SPC AC 151256

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
0656 AM CST Thu Nov 15 2018

Valid 151300Z - 161200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER PARTS OF
EASTERN NORTH CAROLINA...

...SUMMARY...
Isolated damaging gusts and a tornado or two may occur from late
this morning through afternoon over portions of near-coastal eastern
North Carolina.

...Synopsis...
In mid/upper levels, a slow-moving, large-scale ridge will remain
just offshore from the Pacific Coast States through the period. 
Downstream, several shortwave perturbations will rapidly traverse
the northwesterly flow across western Canada and the northern
Plains/upper Midwest regions.  The leading such feature -- now
apparent in moisture-channel imagery over portions of ND -- is
expected to phase with an initially weaker/trailing trough over the
MT/SK border area.  The combined feature will amplify and move
southeastward across the upper Mississippi Valley and Lake Michigan
tonight, reaching western Lower MI and IN by 12Z.  As heights fall
ahead of this process, the strong/closed cyclone now centered near
the Mississippi/Ohio River confluence will eject/accelerate
northeastward generally up the Ohio Valley while gradually
weakening.  By the end of the period, this feature should devolve
into a compact, open-wave trough over the Mid-Atlantic.

At the surface, 11Z analysis showed a low over the Atlantic waters
off the central SC coast, with a cold front southwestward across
east-central/southwestern FL Peninsula.  A sharply defined warm
front, with strong baroclinic gradient reinforced by persistent
precip to its north, was evident from the low offshore the NC coast
just south of buoy 41013.  The low should cross eastern NC through
early afternoon, then deepen and occlude over or barely offshore
from the coastal Delmarva Peninsula through 06Z.  By 12Z, the low
should be located over Long Island or just offshore.  The cold front
is forecast to sweep off the Atlantic coast from NC-FL before 00Z,
while the warm/coastal front preceding the low oscillates inland
over eastern NC just prior to the passage of the low.

...NC near-coastal/Tidewater/Outer Banks region...
Widely scattered to scattered thunderstorms are expected to form
along the cold front near the low, and over the warm sector, through
this afternoon.  Activity will occur in a favorably sheared and
moist environment overlain with low/middle-level lapse rates only
slightly greater than moist adiabatic, keeping buoyancy marginal but
sufficient.  Greatest shear should be near the warm-frontal zone,
with effective-shear vectors of 45-50 kt and effective SRH 300-500
J/kg.  The most unstable scenarios near the central/southern Outer
Banks and southeastern NC beaches yield MLCAPE 500-1000 J/kg with
dew points briefly reaching upper 60s, perhaps low 70s F.  This
buoyancy/shear parameter space will support tornado potential from
any supercells that can form, as well as wind/tornado risk in bowing
modes.

Even this close to the event, short-term guidance differs
importantly on the inland penetration of the favorable warm sector
prior to the passage of the surface low, and to some extent, differs
with the track of the low.  Based on a sampling of forecast
soundings, and modification to the 12Z MHX RAOB, this likely is
related to different treatment of the precip-reinforced static-
stability profile.  Regardless, the threat appears somewhat more
compressed eastward than in the previous outlook, given the
cold-sector precip situation, and supported by guidance consensus. 
The lines are slightly adjusted eastward accordingly.

..Edwards/Marsh.. 11/15/2018

$$