Severe Storm Outlook Narrative (AC)
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393
ACUS01 KWNS 240605
SWODY1
SPC AC 240604

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0104 AM CDT Wed May 24 2017

Valid 241200Z - 251200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS A LARGE
PORTION OF THE SOUTHEAST...

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS SURROUNDING THE
SLIGHT RISK AREA...

...SUMMARY...
Severe storms will be possible Wednesday and Wednesday night across
a large portion of the Southeast. More isolated severe storms will
be possible as far north as the mid-Ohio Valley.

...Synopsis...
As an upper trough crossing southwest Canada and the Pacific
Northwest digs southeast across the northern Intermountain region
with time, a second/mobile trough will across the eastern U.S.
through the period.  A short-wave trough -- embedded within cyclonic
westerly flow around the base of the broader eastern trough -- will
rotate across the Southeast and mid-South region through the
afternoon and evening.

As the aforementioned short-wave trough advances, surface
cyclogenesis is expected over the eastern Tennessee/eastern Kentucky
vicinity during the day, and then shifting north into southwest Ohio
overnight.  As this occurs, a trailing cold front will sweep across
the central Gulf Coast region early and into Georgia and eventually
the Carolinas through the afternoon and evening, while a warm front
lifts north to the North Carolina/Virginia border and lingers there
through the evening.  These fronts -- and the evolving warm sector
-- will support multiple episodes of widespread showers and
thunderstorms through much of the period.

...The Southeast...
A complex scenario appears to be evolving for today, as widespread
cloudiness and ongoing convection casts considerable uncertainty.
As short-wave troughing rotates eastward/northeastward across the
area, southerly/southeasterly flow will become established across
much of the warm sector east and southeast of the developing surface
low.  Strength of ascent spread across the area suggests that
multiple rounds of widespread showers and storms will move across
the area through the period, with at least modest diurnal
destabilization allowing a general increase in convective
coverage/intensity through the afternoon.  Storms are expected to
increase across Florida and southern Georgia from early in the
period through the afternoon, with locally damaging winds likely to
be the primary given moderately strong, deep-layer southwesterly
flow.

Farther north, storms are expected to begin increasing in coverage
across central and northern Georgia and into the Carolinas by
midday/early afternoon, with storm mode likely to be a combination
of cells and broken bands.  Multiple rounds of convection are
expected, with any lack of instability somewhat offset by amply
strong/weakly veering flow with height.  Along with risk for locally
damaging winds and marginal hail, isolated tornadoes will also be
possible.  Greatest risk will likely exist over the western
Carolinas where low-level flow may be most backed in response to the
mid-South cyclogenesis, and north of a weak/secondary warm front
hinted at by the NAM.  Tornado risk may extend as far north as the
main warm front progged to lie over northern North Carolina/southern
Virginia by mid to late afternoon.

Storms/severe risk will likely continue into the evening, gradually
tapering off from southwest to northeast as the cold front advances
across the Southeast.  Risk may linger longest over North Carolina
and southern Virginia, and possibly across portions of central and
southern Florida before decreasing into the overnight hours.

...The mid-South and mid-Ohio Valley...
While questions exist regarding degree of destabilization across
this region, backed low-level flow near and northeast of the
developing surface low expected to shift north across the area
through the day will support favorable veering of the lower
tropospheric wind field with height.  If ample destabilization can
occur, risk for a few stronger storms -- capable of producing
damaging winds along with a tornado or two -- would likely evolve.
Greatest potential for ample CAPE to evolve along with somewhat
stronger deep-layer flow seems to exist across eastern TN/eastern KY
and eastward across the mountains, but will introduce
low-probability risk farther north (into parts of OH/IN) and west
(into central KY and middle TN) given latest model trends.

..Goss.. 05/24/2017

$$



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