SPC AC 150557

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1257 AM CDT Tue May 15 2018

   Valid 151200Z - 161200Z

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS OVER A PORTION
   OF THE NORTHEAST STATES INTO NEW ENGLAND...

   ...SUMMARY...
   Severe thunderstorms, capable of significant damaging wind as well
   as hail and a few tornadoes are forecast across a part of the
   Northeast States and the Middle Atlantic this afternoon into the
   evening. Other strong to severe storms will impact portions of
   northeast New Mexico into the southern Plains with isolated
   downburst winds and hail possible.

   ...Northeast States through Middle Atlantic...

   Low to mid 60s F near-surface dewpoints will accompany a warm front
   into southern New England later today. Early warm advection storms
   now developing over the Mid Atlantic region will probably diminish
   later this morning as initial vorticity maximum and its attendant
   low-level jet move offshore. Diabatic warming is likely south of the
   warm front from southern New England into the Middle Atlantic. The
   eastern expansion of steep lapse rate plume in conjunction with
   low-level theta-e advection and solar insolation should contribute
   to moderate instability with 1500-2000 J/kg MLCAPE. A vorticity
   maximum currently over eastern IL will become absorbed within
   stronger winds aloft situated within southern periphery of the
   synoptic-scale Hudson Bay vortex. This feature will subsequently
   accelerate through the Northeast States and southern New England
   during the day. Current indications are that storms will initiate in
   association with the progressive vorticity maximum as well as along
   a southeast-advancing cold front. Wind profiles aloft will
   strengthen with effective-bulk shear exceeding 50 kt, but low-level
   hodographs may remain somewhat modest due to veered low-level winds.
   The thermodynamic and kinematic environment are expected to become
   very favorable for organized severe storms with potential for a few
   supercells, but storms should eventually evolve into linear segments
   with embedded bowing structures capable of significant wind damage
   from northeast PA into southern NY and southern New England.
   Influence of the marine layer may contribute to a gradual weakening
   as activity approaches the coastal region.

   ...Southern Plains into the lower Mississippi Valley region...

   With steep mid-level lapse rates still in place, the atmosphere will
   likely become moderately to strongly unstable during the afternoon
   across the southern Plains region. Several areas of thunderstorm
   development are expected in this region today including a few strong
   to severe multicells capable of mainly downburst winds in
   association with an MCV that will move from OK into AR during the
   afternoon. 

   Other storms may develop in post-frontal upslope regime over the
   higher terrain of northern NM where vertical shear will be at least
   marginally supportive of some supercell structures. This activity
   will spread east into the High Plains with a threat for mainly
   downburst winds and hail.

   Additional storms are expected farther south across west TX along
   the dryline. These storms should be primarily multicell in
   character, but the thermodynamic environment with 2500-3000 J/kg
   MLCAPE will support a threat for downburst winds and large hail.

   ..Dial/Dean.. 05/15/2018

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