Severe Storm Outlook Narrative (AC)
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000
ACUS02 KWNS 290549
SWODY2
SPC AC 290548

Day 2 Convective Outlook
NWS Storm Prediction Center Norman OK
1248 AM CDT Sat Apr 29 2017

Valid 301200Z - 011200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
THE LOWER/MID MS VALLEY AND SOUTHEAST...

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM THE CENTRAL
GULF COAST TO THE MIDWEST...

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
WESTERN/CENTRAL PA AND THE ADJACENT APPALACHIANS...

...SUMMARY...
Severe thunderstorms will be possible across portions of the
lower/mid Mississippi Valley eastward to Alabama Sunday into Sunday
night. Damaging winds will likely be the primary threat, but large
hail and a couple tornadoes may also be possible. A couple
strong/severe storms may also occur Sunday over parts of western
Pennsylvania and the adjacent Appalachians.

...Synopsis...
A large mid-level closed low will lift northeast from the
southern/central High Plains to the Midwest, as a shortwave trough
rotates around its periphery from Texas into the Ohio Valley. In
turn, expansive cyclonic flow aloft should establish over much of
the contiguous US on Sunday.

...Portions of the mid/lower Mississippi Valley and eastward...
With such an amplified system and strong meridional flow aloft,
multiple areas of convection will likely be ongoing Sunday morning,
with one or more north-south oriented bands of storms across parts
of the lower/mid Mississippi Valleys, likely in advance of the
surface cold front. Across the lower Mississippi Valley, these
storms will push east across Mississippi, encountering fairly rich
low-level moisture and moderate surface-based buoyancy. In turn, a
threat for damaging winds and a line-embedded tornado or two is
possible. This band is forecast to gradually weaken with eastward
extent as it outpaces large-scale ascent and encounters increasing
inhibition. Behind these storms, uncertainty exists with the
potential for re-development of convection along the front (due to
prior convective overturning). Nonetheless, a band of strong/severe
storms may re-organize across parts of Mississippi and Alabama late
Sunday into Sunday night. Convection would likely be focused near
the front, primarily favoring a damaging wind threat. However,
strong low-level shear could also support a couple tornadoes Sunday
night.

Across the mid Mississippi Valley, considerable uncertainty exists
with forecast destabilization, as broad precipitation/cloud cover in
the morning may stunt surface heating. Nonetheless, a pocket of
higher surface dew points across southeast Missouri and southern
Illinois may yield a more vigorous band of convection along the
front during the afternoon, aided by stronger large-scale ascent.
These storms would likely pose a threat for damaging winds and a
couple tornadoes, considering the ambient strong wind field.

...Portions of western/central Pennsylvania and the adjacent
Appalachians...
While large-scale ridging aloft will inhibit convection for part of
the day, subtle height falls, modest warm advection, and orographic
influences will likely favor isolated storms by afternoon.
Sufficient surface moisture/heating and a wind profile veering with
height are expected to encourage occasional updraft
vigor/organization. The strongest cells may be capable of isolated
instances of severe hail, gusty winds, and perhaps a tornado.

..Picca.. 04/29/2017

$$



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