Severe Storm Outlook Narrative (AC)
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000
ACUS01 KWNS 301302
SWODY1
SPC AC 301300

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0800 AM CDT Sun Apr 30 2017

Valid 301300Z - 011200Z

...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
LA/MS/AL...

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM THE GULF
COAST STATES TO MIDWEST...

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM THE GULF
COAST STATES TO MIDWEST AND NORTHERN APPALACHIANS...

...SUMMARY...
Severe thunderstorms capable of damaging winds and tornadoes are
expected today into tonight, especially across the central Gulf
Coast States. Other severe storms could occur as far north as the
Midwest and southern Great Lakes region.

...Lower MS River Valley/Gulf Coast States...
A linearly organized broken cluster of storms is ongoing across
along the LA/MS vicinity, where multiple tornadoes have occurred in
the pre-dawn hours, and extends southward into south-central LA
early this morning. These storms will continue to spread
east-northeastward through the morning/afternoon hours. Although
high-level winds are not overly strong per regional 12Z soundings, a
modest but strengthening westerly component aloft in conjunction
with strong low-level shear, including modestly backed southeasterly
surface winds, will continue to support a mixed convective mode
including embedded supercells/mesovortices capable of tornadoes and
damaging winds. A strong tornado cannot be ruled out. See Mesoscale
Discussion 611 for additional short-term details.

The tornado/damaging wind risk should shift into portions of AL by
this afternoon, including the possibility of some regenerative
development later this afternoon into early evening particularly on
the southern flank of convection/possible outflow amidst moist
confluent low-level flow.

...Midwest/southern Great Lakes and Ohio Valley...
Questions exist regarding the extensiveness and likelihood of
appreciable destabilization later today in a scenario that appears
otherwise very favorable for severe thunderstorms given ample
deep-layer/low-level shear. These uncertainties are related to
extensive convection ongoing early today across the middle MS River
Valley and lower OH Valley, with an east/northeastward-moving MCV
also a factor across eastern IL/northern IN today.

Ahead of the cold front, gradual destabilization should occur into
this afternoon along the southern/eastern fringes of ongoing
precipitation and residual outflows, with the possibility of least
some damaging wind/marginally severe hail risk developing this
afternoon. As the upstream trough approaches the region and surface
low spreads northeastward and deepens, at least a narrow corridor of
modest destabilization could allow for late afternoon and evening
increase in fast-moving storms capable of a severe risk.

..Guyer/Mosier.. 04/30/2017

$$



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