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 Forecast Discussion

  
000
ACUS01 KWNS 230501
SWODY1
SPC AC 230459

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
1159 PM CDT Tue Aug 22 2017

Valid 231200Z - 241200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS THIS AFTERNOON
AND EVENING ACROSS THE SOUTHERN MID-ATLANTIC COAST REGION AND
EASTERN CAROLINAS...

...SUMMARY...
A few strong to severe storms may impact parts of the southern
Mid-Atlantic region and eastern Carolinas this afternoon and
evening. Gusty, damaging winds will be the main threat.

...Synopsis...
A mid-upper level closed low will track northeast across Quebec
through tonight, while a shortwave trough digs southeast from
central Canada toward the Upper Great Lakes region this forecast
period.  This latter system will aid in maintaining a large-scale
trough across much of the Great Lakes, OH Valley into the Northeast
and Mid-Atlantic states, with weak height falls expected across VA
and Carolinas.  At the surface, an area of low pressure will track
across southern to eastern Quebec.  The trailing cold front should
extend through eastern New England to off the northern Mid-Atlantic
coast to central VA, the western Carolinas and into the central Gulf
Coast states at 12Z today.  This boundary will advance toward the
Southeast U.S. and Gulf Coasts, while the northern extent should
clear much of New England by early afternoon. 

...Southeast VA and the eastern Carolinas...
The air mass south of the approaching cold front today remains quite
moist (precipitable water values at or above 2 inches per 00Z
soundings).  Despite weak mid-level lapse rates, the abundant
moisture and surface heating will contribute to the occurrence of
moderate instability (MLCAPE 1000-2000 J/kg).  This combined with
effective bulk shear of 25-30 kt suggests multicell storms/clusters
should be the primary storm mode, with some potential for upscale
growth as storms merge and/or cold pools develop.  A weak mid-level
impulse is expected to shift east from the southern Appalachians
this morning, reaching southeast VA and the eastern Carolinas by
peak heating.  Forcing for ascent attendant to this impulse should
aid in thunderstorm development, with convection forming across the
higher terrain, and along the cold front and a pre-frontal trough. 
Steepening low-level lapse rates and the available moderate
instability should prove sufficient in supporting locally strong to
damaging winds with the stronger/sustained storms this afternoon and
evening.

..Peters/Gleason.. 08/23/2017

$$