Severe Storm Outlook Narrative (AC)
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000
ACUS01 KWNS 010054
SWODY1
SPC AC 010053

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0753 PM CDT Sun Apr 30 2017

Valid 010100Z - 011200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS TONIGHT ACROSS
PARTS OF THE FLORIDA PANHANDLE...SOUTHEASTERN ALABAMA AND ADJACENT
AREAS OF SOUTHWESTERN GEORGIA...

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS
SURROUNDING AREAS OF THE SOUTHEAST AND MUCH OF THE OHIO VALLEY...

...SUMMARY...
Thunderstorms may still impact areas east of the Mississippi Valley
into the western slopes of the Appalachians tonight with at least
some risk for severe weather.

...Discussion...
Models continue to indicate further deepening of an already broad
and deep lower/ mid tropospheric cyclone tonight, with the center
forecast to track from the central Plains/lower Missouri Valley
region toward the Upper Midwest/southern Great Lakes region.  The
potentially broad warm sector of the cyclone, east of the
Mississippi River has been substantially impacted by prior
convective development, particularly a swath east of the lower
Mississippi Valley through much of the Tennessee Valley, in the wake
of the remnants of a significant mesoscale convective system.

With the northeastward advection of elevated mixed layer air from
the Mexican Plateau and intermountain U.S.  disrupted/cut-off., and
the mid-level cold core still generally lagging to the west of the
surface cold front, mid-level lapse rates across much of the warm
sector are rather modest to weak.  And it is not clear that this
will change substantially through the remainder of the period,
though the larger-scale mid-level trough axis is taking on an
increasing negative tilt across the Plains into the Mississippi
Valley.

Still, forcing for ascent has been sufficient to support renewed
scattered thunderstorm development  across central/southern
Illinois, where clockwise curved low-level hodographs remain
characterized by strong to extreme shear,  in the presence of a
moist boundary layer (with mid/upper 60s surface dew points) and at
least weak CAPE.  It may not be out of the question that this
environment could still become supportive of thunderstorms with at
least some risk for tornadoes this evening.

Otherwise, further thunderstorm development remains possible later
tonight ahead of the cold front as it advances east of  the
Mississippi Valley, toward the Appalachians.  With additional
strengthening of southerly 850 mb flow to 50-70+ kt still forecast
ahead of it, this would still seem likely to be accompanied by at
least some risk for potentially damaging wind gusts through the Ohio
Valley and portions of the Tennessee Valley,  and along/south of the
slowing/stalling convective boundary across western Georgia through
the Florida panhandle.  Slight risk probabilities will be maintained
across the Florida panhandle into southeastern Alabama, where there
appears likely to remain a continuing influx of richer boundary
layer moisture (supporting greater potential instability) off the
Gulf of Mexico.

..Kerr.. 05/01/2017

$$


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