Severe Storm Outlook Narrative (AC)
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000
ACUS03 KWNS 240717
SWODY3
SPC AC 240716

Day 3 Convective Outlook
NWS Storm Prediction Center Norman OK
0216 AM CDT Mon Apr 24 2017

Valid 261200Z - 271200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
THE ARKLATEX AND LOWER TO MID MISSISSIPPI VALLEY...

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS OUTSIDE OF THE
SLIGHT RISK AREA ACROSS PARTS OF THE ARKLATEX...SOUTHERN
PLAINS...LOWER TO MID MISSISSIPPI VALLEY AND SOUTHERN GREAT LAKES
REGION...

...SUMMARY...
Scattered severe thunderstorms with large hail, wind damage and
perhaps a tornado or two will be possible across parts of the
Arklatex and lower to mid Mississippi Valley on Wednesday. Other
marginally severe thunderstorms will be possible from Illinois
north-northeastward into the southwestern Great Lakes region.

...Arklatex/Lower to Mid Mississippi Valley...
An upper-level trough is forecast to move across the Great Plains on
Wednesday as a cold front advances eastward across the Ozarks and
Arklatex. Convection is forecast to develop along and behind the
front during the morning across eastern Kansas and western Missouri.
Thunderstorms are forecast to gradually expand in coverage, moving
eastward across Missouri and Arkansas during the afternoon. The
development of a linear MCS appears to be a possibility as the front
moves into the lower to mid Mississippi Valley Wednesday evening.

Ahead of the front, strong moisture advection will increase surface
dewpoints into the mid to upper 60s F from northern Louisiana
northward into southeast Missouri where a corridor of moderate
instability should be in place by afternoon. This combined with 60
to 65 kt of deep-layer shear evident on forecast soundings, should
support a severe threat. The greatest potential for large hail and
possibly a tornado or two, will be associated with supercells early
in the event. However, storms may have trouble remaining discrete
due to a synoptic-scale band of large-scale ascent associated with
the approaching upper-level trough and due to strong low-level
convergence along the front. For this reason, the greatest severe
threat coverage could associated with damaging wind gusts.

...Illinois/Southwestern Great Lakes...
A negatively tilted upper-level trough is forecast to move across
the central Plains and mid Missouri Valley on Wednesday as a cold
front advances eastward across the mid to upper Mississippi Valley.
Surface dewpoints ahead of the front may reach the lower 60S F by
afternoon as convection develops along the front and moves eastward
across the region. In spite of the low-level moisture, instability
should remain weak due to cloud cover and limited surface heating.
Regardless, forecast soundings in Illinois at 00Z/Thursday show
strong deep-layer shear profiles with 0-6 km shear of 50 to 60 kt.
This should be enough for a marginal wind-damage threat associated
with the stronger parts of a line oriented from south-southwest to
north-northeast across Illinois and the southwestern Great Lakes.

..Broyles.. 04/24/2017

$$


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