U.S. Severe Weather Forecast (Convective Outlook)

Day Three

acus03 kwns 240717 
Storm Prediction Center ac 240716 

Day 3 convective outlook 
National Weather Service 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 middle 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 middle Mississippi Valley and southern Great Lakes 

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 mesoscale convective system 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