SPC AC 140448

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1148 PM CDT Sun May 13 2018

   Valid 141200Z - 151200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM THE SOUTHERN
   AND CENTRAL PLAINS THROUGH THE OHIO VALLEY AND MIDDLE ATLANTIC...

   ...SUMMARY...
   Thunderstorms, capable of isolated damaging wind and large hail are
   expected Monday afternoon and evening from parts of the southern
   Plains northeastward to the mid Mississippi Valley. Other severe
   storms with damaging wind will be possible from the mid/upper Ohio
   Valley eastward to the Mid-Atlantic.

   ...Synopsis...

   Synoptic pattern will be characterized by an evolving Rex block over
   the western states with a belt of stronger downstream westerlies
   aloft from the central Plains through the Great Lakes region. A
   series of vorticity maxima embedded within the southwest U.S. cutoff
   upper low will eject northeast contributing to suppression of upper
   ridge situated over the MS Valley. At the surface a quasi-stationary
   front should extend from the Middle Atlantic through the OH Valley
   into southwest KS with a dryline extending south through west TX.
   The circulation associated with a shortwave trough moving northeast
   through the central Plains and into the mid MS valley will
   contribute to the southwest portion of this front advancing
   southeast through KS while the OH Valley portion may move slowly
   north as a warm front. 

   ...Southern and Central Plains region...

   In wake of overnight storms, the Great Plain's warm sector should
   once again become moderately to strongly unstable this afternoon
   with mid 60s F dewpoints beneath steep lapse rates supporting
   2000-3000 J/kg MLCAPE. Frontal convergence, dryline mixing and weak
   impulses embedded within the southwesterly flow regime should
   contribute to the initiation of storms from west TX through parts of
   OK and KS by late afternoon. While weak to modest winds aloft and
   weak vertical shear will support multicell storm modes, the
   thermodynamic environment will promote a threat for downburst winds
   and large hail as storms develop from late afternoon into the
   evening. 

   ...Middle Mississippi Valley into the OH Valley and Mid Atlantic
   region...

   Multiple episodes of storms are expected in this region as
   low-amplitude impulses move through the mean synoptic ridge and
   augment isentropic ascent north of the warm/quasistationary front.
   Potential still exists for a forward propagating MCS to evolve out
   of early storms expected to be ongoing over a portion of the Great
   Lakes and OH Valley region. The downstream atmosphere will become
   moderately unstable and storms should increase in intensity as they
   develop southeast with damaging wind the main threat from the OH
   Valley into the Mid Atlantic during the day.  Other storms will
   likely develop upstream across the middle to upper MS valley during
   the afternoon and especially the evening as the low-level jet
   strengthens. This activity may evolve into muticell clusters/MCS as
   it advances east with damaging wind and hail the main threats.  

   ...Central Rockies...

   Upslope east-northeast low-level flow will persist beneath moderate
   southwesterly winds aloft contributing to 45+ kt effective bulk
   shear. The atmosphere is expected to become marginally unstable
   along the front range and storms will likely develop by late
   afternoon or early evening. This environment should support  some
   supercell structures with large hail the main threat. A weak
   thermodynamic environment remains a potential limiting factor, but
   will continue to monitor for a possible slight risk in later
   updates.

   ..Dial/Dean.. 05/14/2018

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