SPC 2000Z Day 1 Outlook

Day 1 Outlook Image

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
0213 PM CDT Thu Oct 29 2020

Valid 292000Z - 301200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM THE
CAROLINAS INTO SOUTHERN VIRGINIA...

...SUMMARY...
Isolated severe convective gusts and perhaps a tornado may occur
this afternoon into tonight from the Carolinas into southeast
Virginia.

...Carolinas into southern Virginia...
Little change to the outlook at 20Z as storms are expected to form
later this afternoon over northwest SC where low-level lapse rates
are steep. Storms should increase in coverage coincident with
increasing large-scale ascent through the evening into western NC
and southern VA. A southward-moving cold front will limit the
northern extent of the threat area into southern VA, with a moist
and marginally unstable air mass over the Carolinas supporting
isolated severe storms. Poor lapse rates aloft will mitigate the
overall severe risk, but re-adjusting wind profiles in the wake of
Zeta may support mixed-mode storms with locally damaging gusts or a
brief tornado.

..Jewell.. 10/29/2020

.PREV DISCUSSION... /ISSUED 1130 AM CDT Thu Oct 29 2020/

...Carolinas into southeast VA through tonight...
The remnants of tropical cyclone Zeta will move quickly
east-northeastward over VA and reach the Atlantic coast by about mid
afternoon.  Strong wind profiles/shear will accompany this system
across VA until it moves offshore, but buoyancy will be quite
limited in the poor lapse rate environment with the weakening warm
core cyclone.  Thus, only isolated damaging convective gusts and/or
a brief tornado may occur prior to 21z.  Thereafter, the synoptic
midlevel trough over AR will progress eastward to the southern
Appalachians by tonight, and to the Mid-Atlantic coast by the end of
the period.  An associated, weak surface cyclone will move eastward
along the VA/NC border, along a baroclinic zone in the wake of Zeta.
A separate round of convection is expected to form this evening
across the Piedmont in the zone of ascent near the surface cyclone
and along the cold front trailing southward.  The convection will
subsequently spread east-northeastward across the Carolinas and
southeast VA overnight.

Lapse rates aloft will remain rather poor, but lingering
boundary-layer dewpoints in the low 70s will support at least weak
buoyancy rooted at the surface (SBCAPE around 500 J/kg) overnight. 
Long, relatively straight hodographs with effective bulk shear in
excess of 70 kt and ground-relative winds of 50 kt within a few
thousand feet of the surface will support a threat for isolated
damaging gusts with the overnight convection.

To the south, bands of convection persist from the FL Big Bend into
southeast GA along a confluence zone trailing south-southwestward
from Zeta.  Gusty outflow winds may occur with the heavier
convective cores during the next few hours given 40 kt low-level
flow in area VWPs.  However, poor lapse rates will limit updraft
intensity, and relatively moist profiles suggest that strong
downdrafts are also unlikely.  Given the marginal thermodynamic
profiles and some weakening of low-level flow expected this
afternoon, the threat for severe/damaging winds appears to be quite
small.

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