SPC AC 131622

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1122 AM CDT Tue Jun 13 2017

   Valid 131630Z - 141200Z

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS OVER PARTS OF
   EASTERN SD/ND...EASTERN NE...WESTERN MN...AND NORTHWEST IA...

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS OVER PORTIONS
   OF THE EASTERN TX PANHANDLE AND WESTERN OK...

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER MUCH OF THE
   PLAINS STATES...

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER PARTS OF
   SOUTHERN NEW ENGLAND...

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS OVER MUCH OF THE
   PLAINS STATES...

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM NORTHERN OH
   INTO SOUTHERN NEW ENGLAND...

   ...SUMMARY...
   Severe thunderstorms, capable of large hail, damaging winds, and a
   few tornadoes, will be possible across the northern Plains and upper
   Mississippi Valley this afternoon and evening. Farther south across
   the central/southern Plains, scattered severe storms, primarily
   capable of large hail and damaging winds, are expected through the
   evening hours. Isolated severe storms will also be possible across
   southern New England.

   ...Northern Plains...
   An upper cyclone continues to affect the central/northern Rockies
   today, while a series of shortwave troughs rotate through the base
   of the cyclone and into the central/northern Plains.  Strong daytime
   heating and rich low-level moisture will result in high CAPE values
   this afternoon along and east of a surface front/dryline extending
   from the central Dakotas into KS.  Models are consistent in the
   development of thunderstorms along the boundary by late afternoon,
   tracking eastward across the ENH/SLGT risk areas.  Supercells
   capable of large hail and a tornado or two are initial threats, but
   most 12z model solutions suggest a fairly rapid transition to bowing
   structures, with damaging winds becoming the dominant concern as
   storms move into MN.

   Have maintained a small 10% tornado risk area over parts of
   MN/SD/ND.  Rapid recovery behind the morning MCS should result in a
   corridor of favorable environment later today.  Forecast soundings
   in this region show backed low-level winds and strong CAPE. 
   However, confidence in discrete storm initiation along the warm
   front has decreased from previous outlooks, and will be re-addressed
   at 20z.

   ...Southern Plains...
   Full sunshine along the surface dryline/front over west TX/OK and
   parts of KS will result in strong CAPE and scattered thunderstorm
   development by late afternoon.  Deep-layer vertical shear will
   promote rotating storms, with large hail /possibly very large/ and
   damaging wind gusts possible. Given the consistency in 12z model
   guidance regarding the timing/placement of convective development,
   have added a narrow ENH risk zone to parts of western OK and the TX
   Panhandle.

   ...CT/MA...
   Visible satellite imagery shows strong heating occurring over
   southern New England today, where surface dewpoints are in the mid
   60s.  Scattered thunderstorms are likely to develop this afternoon
   as a mid-level trough approaches from the northwest.  Forecast
   soundings are not particularly impressive, with only moderate lapse
   rates and rather weak low-level winds.  However, sufficient CAPE and
   deep layer vertical shear suggest the risk of a few intense cells
   capable of hail and damaging wind gusts.

   ..Hart/Cohen.. 06/13/2017

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