SPC AC 161247

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0747 AM CDT Sun Aug 16 2020

   Valid 161300Z - 171200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS THIS AFTERNOON
   INTO EARLY TONIGHT FROM SOUTHERN NE ACROSS WESTERN KS/EXTREME
   EASTERN CO TO THE OK PANHANDLE...

   ...SUMMARY...
   Severe storms with large hail and damaging winds will be possible
   this afternoon/evening across parts of the central Plains.  Isolated
   severe storms with damaging winds are also expected this
   afternoon/evening from northwest into parts of southeast Texas,
   across southern Arizona, and central Oregon.

   ...Southern NE to western KS this afternoon into early tonight...
   Though drier air has moved southwestward across eastern KS and
   northeastern OK, a corridor of rich low-level moisture
   (boundary-layer dewpoints in the mid 60s to lower 70s) persists
   farther to the west and southwest from western OK into western
   KS/eastern CO.  This moisture resides beneath the eastern extent of
   a steep midlevel lapse rate plume, around the eastern periphery of
   the midlevel high over the Great Basin.  With daytime heating,
   strong buoyancy (MLCAPE in excess of 2500 J/kg) is expected this
   afternoon from southern NE into western KS/eastern CO.

   A weak reinforcing cold front across NE should provide a focus for
   thunderstorm development later this afternoon, mainly west and
   southwest of any early day convection.  Effective bulk shear near 35
   kt and the large CAPE/steep lapse rates will support a threat for
   supercells capable of producing isolated very large hail.  Storms
   that form on the boundary in NE should develop south or
   southwestward toward KS through this evening, with some potential
   for upscale growth into a small cluster.  The steep lapse rates,
   large CAPE and large DCAPE (> 1500 J/kg) will also favor the
   potential for isolated significant outflow gusts.  Additional storms
   may also form along the front/lee trough in eastern CO, and this
   convection may eventually interact with the NE storms.  If
   cell/cluster mergers occur, storms may persist into the overnight
   hours while developing southward across western KS, with a continued
   damaging wind/large hail threat.

   ...Northeast NM/TX Panhandle across north TX this afternoon...
   A surface cold front will continue to move slowly southwestward
   toward north/northwest TX, but progress of the boundary will be
   slowed by deep mixing with strong surface heating across TX. 
   Several multicell clusters may form along the boundary this
   afternoon, with storms subsequently spreading southward through this
   evening.  Given that storms will be forming and moving into an
   environment with hot surface temperatures and large DCAPE, isolated
   damaging/severe outflow gusts can be expected. 

   ...Northern CA midday to central OR this afternoon...
   A cluster of midlevel convection is overspreading the central CA
   coast this morning, where a midlevel moisture plume is interacting
   with the west edge of the steep midlevel lapse rates that extend
   down to just above the surface.  An offshore shortwave trough will
   continue to move north-northeastward toward the OR/WA coasts around
   the northwest periphery of the strong midlevel high over the Great
   Basin.  Likewise, the midlevel moisture plume will spread
   north-northeastward from northern CA into OR today and support a
   continued threat for thunderstorms.  The convection should
   eventually root close to the surface in response to daytime
   heating/mixing, as low-level lapse rates steepen.  The storms will
   still be relatively dry/high-based, may produce a few
   strong/damaging gusts given the steep lapse rate profiles and
   potential for downward momentum transfer of midlevel flow at or
   above 40 kt.

   ...Southern AZ late this afternoon/evening...
   A gradual increase in low-level moisture has occurred overnight
   across southern AZ, partly related to overnight convection near the
   international border.  A weak MCV over Sonora will help augment
   midlevel east-northeasterly flow across southern AZ today, as the
   midlevel high strengthens farther to the northwest.  Deep inverted-v
   profiles and midlevel flow near 20 kt could help a few storm
   clusters move west-southwestward from the Mogollon Rim to the lower
   deserts later this afternoon/evening, with an accompanying threat
   for isolated strong/severe outflow gusts.

   ..Thompson/Gleason.. 08/16/2020

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