SPC AC 181658

   Day 2 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1158 AM CDT Fri Aug 18 2017

   Valid 191200Z - 201200Z

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS MUCH OF
   NORTHERN KS INTO NE...

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM EASTERN OH
   INTO WESTERN PA/NY/WV...

   ...SUMMARY...
   Isolated severe storms are possible from Ohio into western
   Pennsylvania and southwestern New York Saturday afternoon, and over
   the central Plains late afternoon through evening.

   ...Synopsis...
   A broad belt of southwesterly flow aloft will exist across the
   northeastern part of the country, with upper trough shifting
   eastward across the Ohio Valley during the day and into New England
   overnight. At the surface, winds will be primarily westerly across
   the region with the surface low well to the north over Quebec.
   Dewpoints in the lower 60s will remain, which when combined with
   cool air within the thermal trough aloft will result in sufficient
   instability for a few strong storms.

   To the west, shortwave ridging will exist across the Plains, in
   advance of a strong upper trough over western Canada. A surface
   trough will deepen during the day from the central Dakotas into
   western NE and KS, with strong heating and an increasing low-level
   jet aiding in storm development late in the day.

   ...OH into PA...
   An area of rain and thunderstorms is forecast to be ongoing across
   OH Saturday morning, in association with the upper trough axis. Some
   heating may occur along and south of this potential storm track,
   with some increase in intensity expected. Mean winds in the
   low-levels will be relatively weak, but do increase aloft supporting
   some good forward speed. Marginal instability and long hodographs
   may support a few cells with marginal hail.  Gusty winds are most
   likely, but lack of any surface boundaries suggests any threat will
   be tied to potential preexisting area of storms and associated
   outflows.

   ...KS into NE...
   Strong heating will lead to a deep layer of steep lapse rates and
   will make the most of marginal boundary layer moisture to produce
   1500-2000 J/kg MUCAPE. By late in the day, the cap will be eroded
   and veering winds with height/warm advection profiles will aid in
   the development of isolated clusters of storms, initiating in the
   surface trough and developing east/southeastward during the evening
   supported by an increasing low-level jet. Localized wind damage is
   possible, with hail most likely early in the cycle.

   ..Jewell.. 08/18/2017

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