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ACUS01 KWNS 181249

SWODY1

SPC AC 181247



Day 1 Convective Outlook  

NWS Storm Prediction Center Norman OK

0747 AM CDT Thu Apr 18 2024



Valid 181300Z - 191200Z



...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS MAINLY THIS

AFTERNOON INTO EARLY TONIGHT FOR PARTS OF THE MID MS AND LOWER OH

VALLEYS...



...SUMMARY...

Damaging gusts to 70 mph, large hail in excess of 2 inches in

diameter, and a couple of tornadoes are expected mainly this

afternoon into early tonight across the middle Mississippi and lower

Ohio Valleys.  More isolated large hail and damaging winds will be

possible farther south from northern Mississippi and Arkansas into

central Texas.



...Mid MS/lower OH Valleys through tonight...

An occluded cyclone will move eastward into western ON, as part of a

deep mid-upper low over western ON/northern MN by the end of the

period.  Farther to the south, a secondary cyclone will move across

MO to southeast Lower MI in association with an embedded jet on the

southern periphery of the deep midlevel low to the north, as a cold

front progresses southeastward across the mid MS Valley and the

southern Plains.  Ahead of the secondary low and cold front, a

moistening warm sector will spread northeastward from MO to

southern/central IL and southwest IN (boundary-layer dewpoints well

into the 60s) beneath lingering midlevel lapse rates of 7-8 C/km. 

The net result will be an unstable warm sector with MLCAPE near 2000

J/kg and only weak convective inhibition.



The remnants of morning convection across MO could be rejuvenated by

midday-early afternoon, with an intensifying band of storms expected

to spread east-southeastward through the afternoon across the mid MS

Valley and into tonight across the lower OH Valley.  The combination

of moderate-strong buoyancy and sufficient hodograph

length/low-level curvature will support a mix of embedded supercells

and bowing segments capable of producing damaging winds of 60-70

mph, large hail of 1-2.5 inches in diameter, and a couple of

tornadoes.



...AR/southeast OK/north and central TX this afternoon/evening...

Surface heating within an already moist air mass (68-72 F

boundary-layer dewpoints) will drive strong buoyancy (MLCAPE of

2500-3500 J/kg) this afternoon ahead of a surface cold front. 

Scattered thunderstorm development is expected by about 21z along

the front from northwest AR across southeast OK into north and

central TX.  Deep-layer shear will be strong enough for some

supercell structures capable of producing isolated very large hail

(up to 2.5 inches in diameter), along with damaging outflow gusts

given the potential for strong downdrafts.  These storms will last a

few hours into late evening and then weaken as convective inhibition

increases.



...Southeast AR into northern MS this afternoon/evening...

An embedded speed max noted over north TX in the subtropical stream

will progress eastward toward the MS River by late afternoon.  Weak

ascent preceding the wave within an unstable warm sector, along with

surface heating in cloud breaks, could be sufficient for widely

scattered thunderstorm development this afternoon.  If a few storms

do form, the environment will conditionally favor supercells capable

of producing large hail/damaging winds.



..Thompson/Gleason.. 04/18/2024



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