SPC AC 261943

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0243 PM CDT Tue Jun 26 2018

   Valid 262000Z - 271200Z

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS LATE THIS
   AFTERNOON AND EVENING ACROSS PORTIONS OF THE OZARK PLATEAU AND
   ADJACENT MISSISSIPPI VALLEY REGION...

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS SURROUNDING
   AREAS EAST-SOUTHEASTWARD ACROSS THE TENNESSEE VALLEY INTO PARTS OF
   THE SOUTHERN APPALACHIANS...AS WELL AS ACROSS PARTS OF THE NORTHERN
   PLAINS...

   ...SUMMARY...
   Severe thunderstorms are likely from eastern Kansas into central
   Missouri this afternoon into tonight.  Severe storms will also be
   possible this afternoon across Kentucky and parts of the western
   Dakotas.

   ...20Z Outlook Update...
   Considerable adjustments to categorical and probabilistic lines have
   been made, generally to attempt to account for stabilizing impacts
   of ongoing convection and associated outflow.  Moderate to large
   boundary layer CAPE has developed in response to daytime heating,
   largely focused along and south of a conglomerate outflow boundary,
   now roughly extending from eastern portions of the central Plains
   through the Missouri Ozarks into the Tennessee Valley and southern
   Appalachians.  This instability is expected to support a continued
   gradual increase in thunderstorm activity, along the southern
   periphery of broad troughing within the southern branch of the split
   mid-latitude westerlies, where vertical shear appears sufficient to
   contribute to organizing clusters with potentially damaging wind
   gusts the primary severe hazard.

   Across the Upper Midwest, convection continues to gradually increase
   near/just ahead of the eastward advancing mid-level closed low. 
   Mid-level lapse rates appear rather weak, but modest deep layer
   shear could still contribute to organization and some potential for
   strong wind gusts.  Although low-level hodographs and wind fields
   are generally weak, there may be some lingering risk for an isolated
   relatively brief and weak tornado near an effective warm frontal
   zone across parts of northeastern Illinois and adjacent southeastern
   Wisconsin.

   For more specific information concerning ongoing or imminent
   convective potential, please refer to the latest SPC mesoscale
   discussions and watches.

   ..Kerr.. 06/26/2018

   .PREV DISCUSSION... /ISSUED 1130 AM CDT Tue Jun 26 2018/

   ...KY today to MO/KS through tonight...
   A closed midlevel low over IA will continue moving
   east-northeastward toward Lake MI by tonight, in conjunction with an
   associated/weak surface cyclone.  South and southeast of the
   midlevel low, multiple thunderstorm complexes are ongoing this
   morning from western KY to central MO and central KS.  The eastern
   complex will likely persist through the afternoon given that it has
   a well-developed cold pool and surface heating/destabilization to
   its east is already boosting SBCAPE to 3000 J/kg or greater with
   minimal convective inhibition.  Damaging gusts and isolated large
   hail will be the main threats with this convection, plus more
   pulse-type storms farther to the east across KY (ahead of the MCS).

   An outflow boundary trails westward across southern MO, and clusters
   of elevated storms are ongoing atop the cold pool in central MO. 
   The central MO storms will tend to reinforce the cold pool across
   central MO today, but recovery is ongoing across southwest MO where
   temperatures are warming into the 80s with dewpoints in the lower
   70s F.  Continued surface heating/moistening from OK into southeast
   KS/southwest MO will drive strong buoyancy (MLCAPE of 3000-4000
   J/kg) south and west of the current outflows and the synoptic front
   now just south of I-70 in KS.  Meanwhile, a cluster of elevated
   storms (that formed in a warm advection zone this morning) will have
   the potential to become rooted at the surface and generate a cold
   pool as it encounters the increasingly unstable environment toward
   southeast KS this afternoon.  Some combination of growth of the
   morning storms or new development later this afternoon along the
   synoptic front will pose a threat for large hail and damaging winds.
   Low-midlevel vertical shear will be sufficient for some supercell
   structures (and possibly isolated very large hail), though storms
   should tend to grow upscale into another band/cluster and move
   across southeast KS/MO through tonight.

   ...Northwestern IL and vicinity this afternoon/evening...
   Some clouds breaks will allow modest surface heating/destabilization
   to the north of the more widespread convection passing south of this
   area.  A band of ascent attendant to the midlevel low and along the
   surface warm front could support a few relatively low-topped
   rotating storms, with a tornado or two possible.

   ...Northern High Plains this afternoon/evening...
   A midlevel shortwave trough within a broad zone of cyclonic
   mid-upper flow belt will progress eastward across the northern High
   Plains and Prairie provinces through tonight.  An accompanying cold
   front will provide a focus for low-level ascent this
   afternoon/evening into western ND and northwestern SD, where
   residual dewpoints in the lower 60s F and strong surface heating
   will drive moderate buoyancy (MLCAPE of 1500-2000 J/kg.  Deep-layer
   vertical shear and lapse rates will be sufficient for supercells
   capable of producing large hail and damaging winds for a few hours
   this afternoon through this evening.

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