SPC Apr 6, 2017 0600 UTC Day 1 Convective Outlook

SPC 1200Z Day 1 Outlook

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
0109 AM CDT Thu Apr 06 2017

Valid 061200Z - 071200Z

...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS
NORTHEAST NORTH CAROLINA...EASTERN VIRGINIA INTO SOUTHERN MARYLAND
AND THE SOUTHERN DELMARVA PENINSULA...

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS SURROUNDING THE
ENHANCED RISK FROM EASTERN NORTH CAROLINA INTO CENTRAL
VIRGINIA...CENTRAL MARYLAND TO FAR SOUTHERN NEW JERSEY...

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS SURROUNDING THE
SLIGHT RISK FROM NORTHEAST SOUTH CAROLINA...CENTRAL NORTH CAROLINA
TO FAR SOUTHEAST PENNSYLVANIA AND NEW JERSEY...

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS CENTRAL
FLORIDA...

...SUMMARY...
Organized severe storms are expected across parts of the
Mid-Atlantic States, primarily during the morning and early
afternoon hours.  The potential exists for tornadoes and a few
swaths of damaging winds during this time frame.  A lingering
severe-weather threat will be possible across central Florida during
the morning and may continue into the early afternoon.

...Synopsis...
A powerful mid/upper trough will advance towards the East Coast this
forecast period, as a vigorous impulse rotates around its periphery
from the southern Appalachians towards the Mid-Atlantic States by
early afternoon, and then northward through New England tonight. 
Concurrently, a closed low at the center of the trough will deepen
as it moves across the lower Great Lakes region.  The synoptic
surface low is expected to track from northern OH to northern NY,
while secondary surface cyclogenesis should be occurring at the
start of the forecast period in northwest VA.  Surface response to
very strong 12-hour 500-mb height falls of 200-260 meters through
18Z will result in strong deepening of the northwest VA low as it
tracks into Washington D.C./central MD by 18-19Z, and then into
eastern PA by mid-late afternoon.  A cold front trailing to the
south will surge eastward and should move off the Mid-Atlantic coast
by mid afternoon, while the southern advances south across the
Florida Peninsula. 

...Mid-Atlantic States to eastern NC...
To the east of the aforementioned deepening secondary surface low
and attendant cold front, strong southerly low-level winds will be
in the process of transporting moisture poleward, with surface dew
points in the lower 60s reaching eastern VA to central MD this
morning and across the southern Delmarva Peninsula by early
afternoon.  The presence of steep midlevel lapse rates spreading
across the moisture return into this region through 18Z should
result in a moderately unstable warm sector with MUCAPE of 1000-1500
J/kg.  

Thunderstorms should be ongoing at 12Z today from western VA through
central NC to eastern SC.  Given the expected degree of
destabilization ahead of the cold front combined with strong
effective bulk shear and strong forcing for ascent with the midlevel
trough and impulse, thunderstorms should increase in coverage and
intensity through the morning.  Low-level hodograph curvature will
support a tornado threat with any discrete cells ahead of the cold
front.  Meanwhile, increasing forcing for ascent and a somewhat
veer-back-veer vertical wind profile suggests the potential for a
linear mode with damaging winds spreading across the enhanced risk
area this morning into the early afternoon.  This outlook issuance
has expanded the higher severe wind probabilities with some
confidence for significant winds into southern MD and the southern
Delmarva Peninsula, while a similar threat will occur southward into
southeast VA and northeast NC.  A tornado threat will be possible
within the linear structure, given the formation of embedded
circulations.  The overall severe-weather threat should diminish by
mid afternoon as the cold front moves off the Mid-Atlantic coast.  A
few elevated storms producing mainly isolated hail will be possible
into southeast PA and NJ. 

...Central Florida...
Strong to severe storms should be ongoing at the beginning of the
forecast period across central FL, within a moderately unstable and
strongly sheared environment.  A weak lobe of vorticity is expected
to be moving across central FL at 12Z, and should weaken further as
it moves east of the Peninsula by early afternoon.  Veered low-level
winds in the warm sector should be related to reduced convergence in
vicinity of the cold front by early afternoon.  Until that time,
moderate instability and strong deep-layer and low-level shear this
morning suggest a lingering severe-weather threat will be possible
for the first 2-4 hours of the forecast period.  This outlook has
introduced a marginal severe risk for isolated strong winds and
perhaps a tornado.

..Peters/Cook.. 04/06/2017

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