SPC AC 260539

   Day 2 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1239 AM CDT Wed Aug 26 2020

   Valid 271200Z - 281200Z

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

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM THE NORTHERN
   PLAINS THROUGH THE GREAT LAKES AND NORTHEAST STATES...

   ...SUMMARY...
   Severe storms are likely Thursday from a portion of the Northeast
   States, Great Lakes and northern Plains. Damaging wind and large
   hail are the main threats though a few tornadoes are also possible.
   Other severe storms with a threat for tornadoes are possible over a
   portion of the lower Mississippi Valley region.

   ...Lower Great Lakes through Northeast States...

   Early Thursday morning a warm front will extend from northern NY
   southeast into southern New England. This boundary will move east
   during the day, while an upstream cold front advances southeast
   through the lower Great Lakes reaching the Northeast States by late
   Thursday afternoon or evening. Elevated storms should be ongoing
   within zone of ascent on cool side of the warm front from northern
   NY into New England. Overall severe threat with this activity will
   probably remain limited. In wake of morning storms and the passing
   warm front, the advection of rich low-level moisture with upper 60s
   to around 70F dewpoints and diabatic heating should result in
   moderate instability with 1500-2500 J/kg MLCAPE. Additional storms
   will likely develop along lake breezes and pre-frontal boundary and
   spread southeast through a portion of the Northeast States. This
   region will reside within a belt of stronger northwesterly winds
   aloft, with 40-50 kt effective bulk shear supporting fast-moving
   organized storms, including bowing segments and supercells. Most
   CAMs show decent updraft-helicity tracks. Initial storm mode could
   be dominated by supercells, but an eventual evolution to lines and
   bowing segments may occur. All severe hazards are possible, but the
   primary threats should be damaging wind and large hail from mid
   afternoon through early evening. 

   ...Northern Plains through Upper Great Lakes...

   Storms are forecast to be ongoing over a portion of the northern
   High Plains early Thursday, and this activity will probably weaken
   during the day. Reinforcing surge of cooler, dry air will augment
   frontogenetic forcing along pre-existing baroclinic zone from a
   portion of the northern Plains into the Great Lakes where the
   atmosphere will likely become moderately unstable during the
   afternoon. While a capping inversion might inhibit surface-based
   storms over this region much of the day, additional storms will
   likely develop by late afternoon or early evening from SD into
   southern MN and the Great Lakes in association with increasing
   frontogenetic forcing and strengthening low level jet. This area
   will reside within belt of moderate winds aloft with 30-50 kt
   effective bulk shear supportive of organized storms. Primary threats
   will be large hail and damaging wind from late afternoon into the
   evening. Other storms will likely develop in upslope region of
   northern WY and southern MT during the afternoon and spread east
   into the High Plains. Strong vertical shear will support supercell
   structures with large hail and downburst winds the main threats.

   ...Lower Mississippi Valley region...

   Strong wind fields and large hodographs associated with the remnants
   of Laura will spread inland through the lower MS Valley region. The
   risk for a few tornadoes will likely persist with mini supercells in
   the outer bands east and northeast of the center, and a SLGT risk
   has been introduced to reflect this threat.

   ..Dial.. 08/26/2020

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