Severe Storm Outlook Narrative (AC)
Issued by NWS
ACUS11 KWNS 302043
SPC MCD 302042
Mesoscale Discussion 0617
NWS Storm Prediction Center Norman OK
0342 PM CDT Sun Apr 30 2017
Areas affected...south central through northeast Alabama through
middle and southeast Tennessee and northwest Georgia
Concerning...Tornado Watch 182...183...
Valid 302042Z - 302245Z
The severe weather threat for Tornado Watch 182, 183 continues.
SUMMARY...Threat for isolated damaging wind and a couple of
tornadoes should persist through early evening, with greatest threat
expected from Middle Tennessee, northeast Alabama into northwest GA.
DISCUSSION...Line of storms from middle TN through central and
southwest AL is advancing east at 30-40 kt. The most organized
portion of the line with embedded mesovortices and bowing segments
extends from middle TN into northeast AL. The downstream atmosphere
is only marginally unstable with 500-1000 J/kg MLCAPE. However,
surface temperatures are warming into the 80s with steepening
low-level lapse rates. Activity is embedded within strong
unidirectional southerly winds with 40-45 kt 0-6 km shear and around
250 m2/s2 0-1 km storm relative helicity based on current storm
motions. Isolated damaging wind appears to be the primary threat
given a dominant linear mode, through a couple of tornadoes remain
possible with any embedded supercells or mesovortices. Farther
southwest, the more southwesterly orientation of the squall line
relative to the mean deep-layer flow has resulted in a tendency for
updrafts to develop behind the leading outflow, which has limited
the severe threat overall.
...Please see www.spc.noaa.gov for graphic product...
LAT...LON 35748632 36508596 36548489 35508477 34318470 33068484
32468592 31638725 34038579 35748632