SPC AC 061707

   Day 2 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1207 PM CDT Thu Jul 06 2017

   Valid 071200Z - 081200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS OF
   THE OHIO VALLEY...

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM THE
   CENTRAL/NORTHERN HIGH PLAINS SOUTHEASTWARD TO SOUTHERN MISSOURI AND
   NORTHEASTWARD TO THE NORTHEAST...

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
   WISCONSIN...

   ...SUMMARY...
   Strong to severe storms are expected to develop Friday afternoon
   over the Ohio Valley and possibly into a portion of the Northeast
   States. A few other strong to severe storms are possible from the
   mid-Mississippi Valley westward to the central and northern High
   Plains later Friday afternoon and evening.

   ...Synopsis...
   A large-scale mid/upper trough will amplify across portions of the
   eastern U.S., with shortwave troughs migrating the base of this
   trough across the Great Lakes and Northeast.  Farther west, a stout
   mid/upper ridge will remain anchored over the Four Corners and
   Intermountain West.  At the surface, a cold front initially from
   Lower Michigan to Iowa and Nebraska, will migrate southeastward as a
   substantial surface ridge settles into the Northern Plains and upper
   Mississippi Valley.  This front will be the primary impetus for
   scattered strong to severe storms across parts of the Northeast,
   Ohio Valley, and central/northern High Plains especially from Friday
   afternoon into Friday evening.

   ...Ohio Valley into the Northeast...
   Over the course of the afternoon, models indicate that several
   broken bands/linear convective segments will develop initially from
   Indiana/Ohio northeast to the vicinity of Lakes Erie/Ontario -
   perhaps as early as 18Z.  Although low-level shear is fairly weak
   across the region, deep shear will favor storm organization as a
   corridor of enhanced mid-level flow (40-50 knots) overspreads the
   region.  Modest veering of profiles may support updraft rotation in
   isolated updrafts, although broken linear segments should foster a
   hail/damaging wind threat especially in portions of the Ohio Valley
   where surface-based instability will be maximized (around 2000-3000
   J/kg MUCAPE).  Farther northeast, weaker buoyancy over New
   York/Pennsylvania may result in a more isolated threat for damaging
   wind gusts, and only 5%/marginal probabilities are retained in that
   area for this forecast. 

   ...Southeastern Kansas/northern Oklahoma into western Kentucky...
   At least isolated convective activity will develop along a
   southeastward-moving cold front across the region during peak
   heating hours as model point forecast soundings indicate minimal
   inhibition amidst moderate to strong instability (3000-4000 J/kg
   MUCAPE).  Deep shear profiles are somewhat weaker than farther
   northeast as the region resides on the southern fringe of stronger
   flow to the north.  However, the presence of modest deep shear for
   storm organization suggests at least an isolated potential for
   damaging downburst winds and large hail given steep mid-level lapse
   rates (and assuming at least isolated convective coverage). 
   5%/marginal severe probabilities extend into this region to address
   the isolated severe threat.

   ...Portions of the Plains from southwestern South Dakota into
   central Kansas...
   The aforementioned cold front should extend from central Kansas
   westward to northeastern Colorado by mid-afternoon, with
   easterly/upslope surface wind fields across the High Plains. 
   Scattered strong to severe thunderstorms are expected to develop by
   the afternoon (especially across the High Plains), with perhaps some
   evolution into clusters/linear segments into the evening.  The
   presence of a northwest-to-southeast oriented axis of moderate
   instability and 20-30 knot northwesterly surface flow suggests that
   storms will tend to propagate southeastward toward central Kansas
   into the evening hours.  At least an isolated severe hail and wind
   threat will exist with this activity, with a potential for an
   upgrade to Slight risk in later outlooks once uncertainties
   regarding convective coverage of storms can be resolved.

   ...Wisconsin...
   A shortwave trough axis will approach the region during the
   afternoon as surface temperatures rise into the 70s and low 80s F. 
   The region will also reside beneath the left exit region of a
   mid-level jet max over Iowa and Illinois.  Moderate instability and
   the aforementioned sources of lift will foster scattered
   thunderstorm development, with perhaps a few 1" hail stones and
   near-severe wind gusts occurring in the strongest activity. 
   5%/marginal severe probabilities have been added to this outlook for
   these reasons.

   ..Cook.. 07/06/2017

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