SPC AC 300541

   Day 2 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1241 AM CDT Fri Jun 30 2017

   Valid 011200Z - 021200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
   THE NORTHEAST...

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS OUTSIDE OF THE
   SLIGHT RISK AREA FROM PARTS OF THE NORTHEAST WEST-SOUTHWESTWARD INTO
   THE SOUTHERN PLAINS...

   ...SUMMARY...
   Severe thunderstorms associated with damaging wind gusts and
   isolated large hail will be possible across the Northeast Saturday
   afternoon into early evening. Marginally severe storms will be
   possible from the southern Plains east-northeastward into the
   central Appalachians.

   ...Northeast...
   An upper-level trough will move across the Great Lakes on Saturday
   with southwest mid-level flow across the Northeast. At the surface,
   a cold front will advance eastward across the lower Great Lakes and
   into the Northeast by Saturday afternoon. Thunderstorms will
   probably be ongoing along the front during the morning with a marked
   increase in convective coverage taking place in the afternoon.
   Warming surface temperatures ahead of the front should result in a
   corridor of moderate instability by afternoon. As this occurs,
   storms should become increasingly organized along the cold front.
   Other storms should develop eastward along a warm front moving
   through northern New York and New England. Multiple line segments
   will be possible across the slight risk area during the afternoon
   and early evening.

   GFS forecast soundings along the instability axis in the Northeast
   at 21Z on Saturday show moderate deep-layer shear profiles with
   gradually veering winds with height and about 50 kt of
   west-southwesterly flow at upper levels. This will support supercell
   development with storms that can remain discrete or with the
   stronger cells embedded in a line. Supercells will have potential to
   produce isolated large hail. The stronger supercells may have an
   isolated tornado threat especially along the warm front in northern
   New York and Vermont. The greater threat may be damaging wind gusts
   as a line of storms organizes across the Northeast. Damaging wind
   gusts will be most likely with bowing structures.

   ...Southern Plains/Mid Mississippi Valley/Central Appalachians...
   An upper-level trough will move eastward across the Mississippi
   Valley on Saturday as a cold front advances southeastward across the
   mid Mississippi Valley and Central Appalachians. Surface heating
   ahead of the front along with dewpoints in the mid to upper 60s F
   should result in pockets of moderate instability during the
   afternoon. Thunderstorms that can develop along the front may have a
   marginal wind-damage threat mainly in areas with moderate
   instability and steep low-level lapse rates. 

   Farther west across the southern Plains, the front is expected to
   stall in the Red River Valley where surface dewpoints should be in
   the upper 60s and lower 70s F. The GFS and NAM solutions suggest
   that a pocket of strong instability will be possible in the Red
   River Valley Saturday afternoon. In spite of this, deep-layer shear
   profiles should remain relatively weak. This should keep any severe
   threat marginal across the Southern Plains with strong wind gusts
   and hail the primary threats.

   ..Broyles.. 06/30/2017

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