SPC Apr 27, 2017 2000 UTC Day 1 Convective Outlook

SPC 2000Z Day 1 Outlook

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
0300 PM CDT Thu Apr 27 2017

Valid 272000Z - 281200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM PARTS OF
THE SOUTHEAST U.S. NORTHWARD INTO THE LOWER GREAT LAKES...

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FOR PORTIONS OF
THE CENTRAL AND SOUTHERN HIGH PLAINS...

...SUMMARY...
A few storms capable of damaging winds and perhaps hail or a tornado
will be possible over parts of Georgia and South Carolina. 
Otherwise, isolated severe wind gusts may accompany thunderstorms
from portions of the lower Great Lakes region to the Southeast
States today into this evening, and across portions of the central
and southern Great Plains late this afternoon into this evening.

...discussion...
The only change from the earlier outlook is to reduce wind
probabilities from 15% to 5% for the GA/SC area.  As the Great Lakes
upper system becomes increasingly displaced from the GA/SC area,
weakening upper support will likely lead to less overall risk for
wind damage due in part to the lack of a linear mode and stronger
forcing for ascent.  

Elsewhere, the outlook was not adjusted substantially.

..Smith.. 04/27/2017

.PREV DISCUSSION... /ISSUED 1127 AM CDT Thu Apr 27 2017/

...GA/SC...
An ongoing band of strong thunderstorms continues to occasionally
show low/mid level rotation and indications of severe threat.  This
scenario will likely continue through the afternoon as more storms
form eastward across central GA and eventually into western SC. 
Local VAD profiles and forecast soundings suggest that low/deep
layer shear is favorable for organized thunderstorms including
supercells and bowing structures.  Continued daytime heating and
destabilization along the southern fringe of cloud cover across the
risk area would support an upgrade to SLGT risk.  Locally damaging
wind gusts are probably the main threat in the strongest cells. 
However, an isolated tornado or two, along with some hail, is
possible.

...OH/PA/NY/WV/VA...
The latest surface analysis shows a cold front sweeping eastward
across Lower MI and western OH. Only broken cloud cover ahead of the
front is helping surface temperatures to climb through the mid 70s,
resulting in steep low-level lapse rates and marginal instability.
12z CAM solutions are relatively consistent that scattered showers
and thunderstorm development this afternoon along/ahead of the front
from eastern OH into much of WV and western PA.  The storms will
eventually spread into central PA/VA and western MD this evening. 
Strongly considered an upgrade to SLGT over parts of this corridor. 
However, forecast soundings suggest very little CAPE and mid-level
lapse rate only in the 6.0 C/km range.  It is likely that a few
fast-moving showers and thunderstorms will pose a risk of
gusty/damaging wind gusts this afternoon.  This region will be
re-evaluated for an upgrade to SLGT at 20z.

...CO/KS/OK/TX...
A few high-based thunderstorms are expected this afternoon and early
evening over parts of southeast CO, southwest KS, and portions of
the TX/OK Panhandles.  Instability will be quite limited.  However,
steep mid level lapse rates and favorable wind fields suggest some
risk of hail and gusty winds in the strongest cells.

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