SPC AC 280717

   Day 3 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0217 AM CDT Tue Jul 28 2020

   Valid 301200Z - 311200Z

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS THURSDAY
   AFTERNOON INTO THURSDAY NIGHT ACROSS PARTS OF SOUTHERN KANSAS...MUCH
   OF OKLAHOMA AND THE NORTHEASTERN TEXAS PANHANDLE...

   ...SUMMARY...
   Strong thunderstorms may impact parts of the south central Great
   Plains late Thursday into Thursday night, accompanied by at least
   some potential for severe wind gusts.

   ...Synopsis...
   Mid-level ridging may continue to build across much of the northern
   intermountain region and northern U.S. Rockies through much of
   western Canada during this period, downstream of an initially broad
   and deep mid-level low over the northeastern Pacific.  As this
   occurs, it appears that the mid-level low may begin to undergo
   considerable deformation, as it is forced eastward and northeastward
   with the approach of a vigorous upstream impulse within the
   mid-latitude westerlies.  Models continue to suggest that this will
   include a transition to negatively tilted troughing, which may
   approach the British Columbia and Pacific Northwest coast by late
   Thursday night.

   Meanwhile, within one branch of westerlies downstream of the
   ridging, a significant upper trough is forecast to continue
   gradually progressing into and across the northern Atlantic Coast
   states, as consolidating upstream perturbations begin to dig into
   the Hudson Bay vicinity.  

   Another weaker branch of westerlies will linger to the southwest and
   south, with perhaps the most significant embedded impulse continuing
   to gradually dig to the lee of the Wyoming/Colorado Rockies.  It
   appears that this may contribute to amplifying larger-scale
   troughing across south central portions of the Great Plains.  This
   may be preceded by several convectively generated or enhanced
   perturbations across the Ozark Plateau and Tennessee Valley into the
   southern Mid Atlantic coast vicinity.

   Highest thunderstorm probabilities for Thursday through Thursday
   night probably will remain focused with the higher moisture content
   along this weaker/southern branch.

   ...South central portions of the Great Plains...
   In the wake of one convectively generated perturbation (progressing
   across and east of the Ozark Plateau/Mid South), and ahead of the
   short wave digging to the lee of the Rockies, a plume of elevated
   mixed-layer air may advect southeastward across much of the southern
   Great Plains.  Beneath this air mass, it appears that strong
   differential surface heating may contribute to a strengthening
   baroclinic zone near/north of the Red River into southwestern
   Kansas.  This may become a focus for substantive destabilization
   (CAPE in excess of 2000 J/kg) in the presence of moderate to strong
   shear, beneath northwesterly mid-level flow strengthening to 30-40
   kt.  

   Aided by forcing for ascent associated with digging impulse, it is
   possible that the environment could become conducive to the
   evolution of an organized, southeastward propagating cluster of
   thunderstorms, with the potential to produce severe wind gusts,
   sometime late Thursday or Thursday night.

   ..Kerr.. 07/28/2020

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