SPC AC 151954

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0254 PM CDT Sat Aug 15 2020

   Valid 152000Z - 161200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS NORTHERN MN
   AND THE SOUTH-CENTRAL PLAINS...

   ...SUMMARY...
   Scattered severe storms will be possible across northern Minnesota
   and a portion of the south-central High Plains during the late
   afternoon and early evening.

   ...Southern High Plains...

   The Slight risk has been trimmed on the southern and western flank
   across parts of the TX Panhandle into northeast NM and southeast CO.
   Strong capping remains across the region and water vapor loops show
   possible subsidence and a large area of relatively dry air over the
   region. Forecast soundings maintain moderate to strong capping into
   the evening hours across parts of the area and this should limit
   storm intensity. Further east across the Slight risk area toward far
   eastern CO and western KS, capping is not as strong and instability
   is greater. Additionally, this area could experience a boost as it
   remains on the southern fringes for stronger 0-6 km shear. As any
   weaker convection moves into this area off of the higher terrain,
   these factors may provide a more favorable environment, relative to
   further west, for storm intensification and organization through the
   evening hours. 

   ...Western NE to southern SD...

   Minor adjustments have been made to the Marginal risk and 10%
   general thunder lines across western NE into southern SD. Moderate
   0-6 km shear exists across the region, and deepening CU has been
   noted along a surface trough extending from the eastern NE Panhandle
   northeastward into adjacent portions of southwestern/south-central
   SD. Instability has increased to around 500-1500 J/kg along this
   zone as capping continues to erode. A severe-warned storm is already
   occurring over Sheridan County NE and additional cells could develop
   northeastward along the surface trough through early evening. Gusty
   winds and hail may accompany the strongest cells, and the Marginal
   has been adjusted modestly to the northeast to account for this
   potential.

   ..Leitman.. 08/15/2020

   .PREV DISCUSSION... /ISSUED 1129 AM CDT Sat Aug 15 2020/

   ...Northern MN...
   The left-exit region of an embedded mid-upper speed max over
   the Prairie Provinces will translate southeast across the Red River
   Valley by early evening. While boundary-layer dew points should
   largely hover around the mid 50s in the wake of convection and a
   cold frontal passage yesterday, cooling mid-level temperatures and
   robust surface heating should support MLCAPE of 500-1000 J/kg.
   Deep-layer vertical shear will be sufficient for a few supercells
   and multicell clusters during the late afternoon to mid evening,
   with a primary risk of severe hail.

   ...South-central High Plains...
   Weak low-level easterlies have yielded upper 50s to mid 60s surface
   dew points across the region. Surface heating beneath steep
   mid-level lapse rates will result in a plume of moderate-strong
   buoyancy at peak heating (MLCAPE of 2000-3000 J/kg), within a modest
   northwest flow regime aloft characterized by effective bulk shear
   increasing to near 30 kts. This will conditionally support a few
   transient supercells and multicell clusters.

   Storm initiation north of the Palmer Divide is highly questionable
   given upstream mid-level drying overspreading the region per water
   vapor imagery and minimal simulated convection in morning guidance.
   Greater confidence in convective development is off the Sangre de
   Cristos and Raton Mesa region. This activity should develop along
   the periphery of the buoyancy plume and its uncertain whether it can
   spread northeast towards the richer low-level moisture centered on
   southwest KS prior to nocturnal MLCIN increase. Convection may tend
   to spread southeast in the weaker shear regime of eastern NM and the
   western TX Panhandle. Otherwise, low-level warm advection may yield
   a cluster of overnight/early morning convection across
   southwest/south-central KS and northwest OK with perhaps a marginal
   severe risk.

   ...IL to the Ozarks...
   A weakly convergent cold front slowly settling southeastward should
   be the focus for isolated late afternoon and early evening
   thunderstorms. A confluent belt of modest 20-25 kt mid-level
   northwesterlies should overlie this portion of the front, with the
   greatest buoyancy expected from MO southwestward. Setup should
   support isolated damaging winds region wide, with some hail also
   possible over the Ozarks.

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