SPC AC 241950

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0250 PM CDT Sun Oct 24 2021

   Valid 242000Z - 251200Z

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS FROM THE OZARKS
   AREA INTO THE MIDDLE MISSISSIPPI VALLEY REGION...

   ...SUMMARY...
   Scattered severe thunderstorms with damaging wind gusts, large hail
   and a couple of strong tornadoes are likely from parts of the Ozarks
   into the middle Mississippi Valley the remainder of this afternoon
   into tonight. Isolated damaging gusts and a tornado or two will also
   be possible along the Oregon coast.

   ...Ozarks through the middle Mississippi Valley region...

   Scattered thunderstorms including a few supercells are underway over
   northwest MO within zone of deeper forcing ahead of the upper
   vorticity maximum and surface low. Additional storms will soon
   increase in coverage and intensity farther south along the cold
   front. These storms will continue east through a corridor of
   moderate surface-based instability with 1500-2000 J/kg MLCAPE, 40-50
   kt effective bulk shear and 200-300 m2/s2 0-1 km storm relative
   helicity. Mixed storm modes with both supercells and line segments
   are likely into the evening. A few discrete pre-frontal storms are
   also possible. All hazards are expected including the potential for
   a few strong tornadoes into the evening.

   ..Dial.. 10/24/2021

   .PREV DISCUSSION... /ISSUED 1152 AM CDT Sun Oct 24 2021/

   ...Ozarks to Mid MS Valley this afternoon into tonight...
   A midlevel shortwave trough over central KS as of late morning will
   progress to MO later this afternoon and IL/IN overnight, and will be
   preceded by a surface cyclone across northern MO this afternoon into
   northern IL/IN tonight.  South of the surface cyclone, a cold front
   will move eastward/southeastward from eastern KS/OK across MO/IL/AR
   through tonight.  The focus for severe storms will be along and just
   ahead of the cold front, with the surface warm front delineating the
   northern extent of the main tornado/wind threat.

   Mid 60s boundary-layer dewpoints will continue to spread
   north-northeastward in the warm sector from OK/AR to MO/IL through
   this evening in advance of the cold front.  The moistening will
   occur beneath midlevel lapse rates near 8 C/km, and will combine
   with daytime heating to support MLCAPE values around 2000 J/kg and
   weakening convective inhibition by mid afternoon.  Thunderstorm
   development is anticipated by 19-21z in broken bands along and 1-2
   counties ahead of the cold front (as evidenced by the weak
   pre-frontal convection now forming in east/southeast KS), and storms
   will move northeastward into the warm front zone in MO and into west
   central IL later this afternoon/evening.  Additional storm
   development will occur southwestward into eastern OK/western AR. 
   Frontal forcing for ascent typically favors squall line development,
   though there is some potential for semi-discrete supercells given
   relatively fast storm motions compared to frontal motion, and
   substantial cross-frontal deep-layer flow/shear.  Long hodographs
   (effective bulk shear of 40-50 kt) and some low-level hodograph
   curvature (effective SRH 200-300 m2/s2, especially east of the cold
   front in the open warm sector) will favor supercells initially with
   the potential to produce tornadoes (a few of which could be strong),
   in addition to damaging winds and large hail.  

   The severe threat will transition more to damaging winds by late
   evening and early tonight, though supercells will still be possible
   into AR, with QLCS mesovortices and some tornado potential farther
   north in MO/IL.

   ...OR coast and vicinity this afternoon...
   A deep, occluded cyclone near 46 N and 131 W will move toward
   Vancouver, while the associated baroclinic zone moves inland across
   the Pacific Northwest coast today.  Very strong wind profile/long
   hodographs and weak buoyancy close to the coast could sustain an
   isolated damaging wind/tornado threat along the coast with
   low-topped convection spreading inland, mainly this afternoon.

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