SPC AC 140559

   Day 2 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1259 AM CDT Tue Aug 14 2018

   Valid 151200Z - 161200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER A PORTION OF
   WESTERN NEBRASKA...

   ...SUMMARY...
   A few severe storms are possible, mainly over the central High
   Plains Wednesday afternoon and evening. Isolated strong to severe
   storms will also be possible over the middle Mississippi Valley
   region as well as New England.

   ...Synopsis...

   A rather complex upper pattern will persist through Wednesday with
   cutoff low now over the Mid Atlantic transitioning to a progressive
   open wave and moving offshore early in the period. The upper low now
   over western OK will deamplify as it moves through the mid MS
   Valley. Farther west, a shortwave trough is forecast to become
   cutoff from belt of stronger westerlies and advance through the
   northern High Plains. At the surface a cold front will advance
   southeast through New England with trailing portion into NE, where
   it will likely stall. A weak surface low accompanied by a surface
   trough or weak front will accompany the shortwave trough through the
   middle MS Valley region. 

   ...Central High Plains...

   East to southeasterly low-level winds will reside in vicinity of and
   north of front across northern NE into southern SD, maintaining
   influx of upper 50s to near 60 F dewpoints beneath modest (7-7.5)
   mid-level lapse rates. Showers and storms may be ongoing across SD
   within zone of ascent north of front and immediately downstream of
   the progressive shortwave trough. However, diabatic heating should
   promote destabilization of the surface layer south of front with up
   to 1500 J/kg MLCAPE expected. Mid-upper jet within the base of the
   trough will contribute to 40-45 kt effective bulk shear across
   western NE, and storms are expected to redevelop as the boundary
   layer destabilizes during the afternoon. A few supercells capable of
   large hail and downburst winds will be the main threats.

   Additional storms will probably develop farther south over the
   higher terrain of CO and northern NM and spread east into the High
   Plains. While vertical shear will be weaker, supporting mostly
   multicells, the thermodynamic environment may promote a modest
   threat for a isolated large hail and downburst winds through early
   evening. 

   ...Middle Mississippi Valley region...

   Thunderstorms will likely redevelop within the plume of subtropical
   moisture accompanying a deamplifying shortwave trough and
   convectively enhanced boundaries. Weak lapse rates, areas of clouds
   and ongoing precipitation and weak vertical shear should limit
   overall severe threat. However, 30-35 kt flow in the 850-500 mb
   layer accompanying the shortwave trough suggests where diabatic
   heating occurs, a few storms could pose a threat for locally strong
   wind gusts from afternoon into early evening.  
    
   ...New England...

   At least isolated storms are expected to develop along and ahead of
   the shortwave trough and attendant cold front by late afternoon or
   early evening. Temperatures are not expected to be overly warm but
   dewpoints in the low to mid 60s will help foster enough instability
   for a few stronger storms capable of mainly isolated strong wind
   gusts.

   ...MAXIMUM RISK BY HAZARD...
   Tornado:   2%     - Marginal
   Wind:     15%     - Slight
   Hail:     15%     - Slight

   ..Dial.. 08/14/2018

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