SPC 0700Z Day 2 Outlook

Day 2 Outlook Image

Day 2 Convective Outlook  
NWS Storm Prediction Center Norman OK
1148 PM CST Mon Dec 14 2020

Valid 161200Z - 171200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS WEDNESDAY ACROSS
PARTS OF EASTERN NORTH CAROLINA AND GULF COASTAL PORTIONS OF THE
NORTHERN FLORIDA PENINSULA...

...SUMMARY...
Strong thunderstorms may impact parts of the Outer and Inner Banks
vicinity of North Carolina and Gulf coastal areas of the northern
Florida Peninsula Wednesday, posing at least some risk for severe
weather.

...Synopsis...
As mid/upper flow continues to trend more zonal across Canada, a
broad west-northwesterly belt of westerlies emanating from the
mid-latitude Pacific will maintain considerable influence across
much of the U.S. through this period.  This regime will include a
number of short wave troughs progressing inland of the Pacific
coast, and across and east of the Rockies.  However, stable
conditions present across much of the nation are expected to
generally be maintained, to the north and west of a broad
northwestward sloping frontal zone initially extending across the
middle and south Atlantic Seaboard into the northern Gulf of Mexico.

Aside from portions of northern Florida, the surface front is still
expected to be offshore.  However, models indicate that low-level
moisture return will be ongoing above the frontal inversion, inland
of coastal areas, ahead of a vigorous remnant mid-level perturbation
rapidly accelerating northeast of the lower Mississippi Valley. 
This may at least initially include a 90-100 kt 500 mb jet streak.

As the mid-level perturbation approaches the Mid Atlantic Coast
region during the day, associated large-scale forcing for ascent and
elevated moisture return may contribute areas of very weak CAPE, and
perhaps thermodynamic profiles supportive of scattered convection
capable of producing lightning.  At the same time, one initial
surface frontal wave is expected to weaken while migrating inland
off the northeastern Gulf of Mexico, through northern Florida, as
another, initially off the South Carolina coast, undergoes
considerable deepening.  The center of the developing cyclone may
migrate inland across parts of the North Carolina coastal plain by
late Wednesday afternoon, before redeveloping east of the Mid
Atlantic coast Wednesday night. 

...Eastern North Carolina...
Due to lingering spread among the output of the various models, the
extent of severe weather potential for Wednesday remains at least
somewhat unclear.  It still appears that the track of the deepening
surface cyclone may allow for at least a weakly destabilizing warm
sector boundary layer to overspread the Outer and Inner Banks
vicinity by Wednesday afternoon.  If this occurs, deep-layer wind
fields and shear probably will become sufficiently strong to support
a risk for organized severe convection.  

The 15/00Z NAM forecast soundings for the Morehead City and Cape
Hatteras vicinities (around the 16/21-23Z time frame) exhibit wind
profiles characterized by strong deep-layer shear and very large
clockwise curved low-level hodographs, which appear favorable for
supercells capable of producing a strong tornado.  Output from other
models doesn't appear quite as favorable, but this will be monitored
in later outlooks for this time period.

....Northern Florida/Florida Peninsula...
Models continue to suggest that the environment over the
northeastern Gulf of Mexico could become supportive of an organized
cluster of storms by 12Z Wednesday.  It appears that this will
advect into coastal areas between Tampa and the Big Bend during the
day, in the presence of 30-50 kt west-southwesterly deep-layer mean
flow.  Although inflow into a potentially vigorous leading line
probably will become characterized by progressively weaker CAPE
across the coastal waters and inland, there still appears at least
some potential that this activity could be accompanied by a risk for
damaging wind gusts and/or a tornado or two into coastal areas
before diminishing.

..Kerr.. 12/15/2020

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