SPC AC 282005

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0305 PM CDT Sat Jul 28 2018

   Valid 282000Z - 291200Z

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS FROM SOUTHEAST
   WY INTO SOUTHWEST NE...NORTHEAST CO AND MUCH OF WESTERN KS...

   ...SUMMARY...
   Scattered to numerous severe storms are likely from the lee of the
   central and southern Rockies east across the central Great Plains
   during the late afternoon into tonight. Very large hail, damaging
   wind gusts, and a few tornadoes are possible.

   ...Central Great Plains...

   The sig wind delineation has been moved from southwest KS, into
   portions of southwest NE/northeast CO and northwest KS.
   Thunderstorms are still expected to develop across eastern CO and
   move into southwest KS, but confidence in sig wind potential has
   decreased somewhat based on latest hi-res guidance. The 30% wind
   area has been expanded northeastward toward central NE. Latest
   guidance continues to suggest that an intense bowing MCS will track
   southeast across western and central NE and northwest KS this
   evening, possibly leading to a more widespread damaging wind event
   and resulting in the shift in sig wind potential. This scenario is
   further supported by 18z and 19z RAOBs from DNR, LBF and DDC which
   show very steep lapse rates near 8 C/km and strong deep layer
   northwesterly shear.

   Elsewhere, previous outlook is on track and no changes have been
   made.

   ..Leitman.. 07/28/2018

   .PREV DISCUSSION... /ISSUED 1129 AM CDT Sat Jul 28 2018/

   ...Lee of the central/southern Rockies to the central Great
   Plains...
   Scattered storms will again develop over the higher terrain of
   central/eastern WY to north-central CO and spread east across the
   adjacent High Plains during the late afternoon to early evening. In
   this region, the presence of mid 50s to lower 60s surface dew points
   amid steep mid-level lapse rates will foster moderate buoyancy with
   MLCAPE of 1000-2000 J/kg. Guidance is consistent in amplifying a
   mid-level speed max within the belt of confluent westerlies across
   this same region, yielding very strong effective shear of 50-70 kt.
   Highly elongated hodographs may support several splitting supercells
   with very large hail and a few tornadoes as the primary initial
   hazards. With a reservoir of maximum buoyancy expected to be
   centered in western KS, storm-scale consolidation into an MCS should
   occur, but this process may be delayed to the late evening given the
   degree of deep-layer shear favoring maintenance of mid-level updraft
   rotation. Once this occurs, severe wind gusts should be the
   predominant hazard until activity finally weakens overnight.

   ...New England...
   Isolated to scattered storms are expected to develop along a weak
   cold front/surface trough downstream of a couple of vorticity lobes
   rotating around the broader upper trough centered over western
   Quebec. Mid to upper-level speed shear will be very strong owing to
   a 90-110 kt 250-mb jet. While near-moist adiabatic lapse rates in
   the mid to upper levels will curtail updraft acceleration and
   overall buoyancy, diabatic heating of a boundary layer consisting of
   mid-upper 60s surface dew points should support MLCAPE of 750-1500
   J/kg. This should yield effective shear of 35-40 kt supporting
   high-level updraft rotation, in spite of weak low-level winds.
   Convection should predominately be discrete with some clustering
   during the early evening. Isolated severe hail and damaging winds
   from strong wind gusts are anticipated.

   ...Ozarks to Arklatex...
   Scattered storms evolving into multicell clusters are expected
   through this evening, offering isolated damaging gusts. The
   strongest storms will probably form in association with the western
   extent of multiple MCVs present from east-central KS south-southwest
   to the south-central OK/north-central TX border. Ongoing cloud
   coverage associated with convection farther east of these MCVs will
   mitigate greater downstream destabilization and weak low-level winds
   will limit hodograph size. 

   ...Central/southern AZ...
   Scattered storms will develop along the Mogollon Rim and over the
   higher terrain of southeast AZ. With 15-20 kt mid-level easterlies
   anticipated during the early evening, some of this activity should
   consolidate into a west-southwestward propagating multicell cluster
   towards the lower desert. DCAPE around 1200-1800 J/kg will favor
   strong to isolated severe wind gusts potentially affecting the
   Phoenix and Tucson metro areas during the evening.

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