SPC AC 281251

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0751 AM CDT Sun Jun 28 2020

   Valid 281300Z - 291200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS PARTS OF THE
   NORTH-CENTRAL AND EASTERN STATES...

   ...SUMMARY...
   Scattered severe storms with a couple tornadoes, large hail, and
   damaging winds are possible from western Iowa to southern Minnesota
   during the late afternoon into tonight. Scattered severe storms with
   mainly a hail and wind threat are possible this afternoon and
   evening in the northern High Plains. Scattered damaging winds are
   possible across the southern Appalachians, as well from the Upper
   Delaware Valley across southern New England this afternoon.

   ...Northern High Plains and central Rockies...
   A mid/upper trough over the Northwest will further dig across the
   Intermountain West and Great Basin today. A swath of 50+ kt 500-mb
   southwesterlies should be centered from northern UT into southeast
   MT by 00Z, thereafter becoming increasingly meridional as the trough
   slowly pivots eastward tonight. 

   Initial afternoon thunderstorm development is expected across the
   central Rockies portion of WY as weak surface-based buoyancy
   develops amid strong deep-layer shear. This activity will spread
   northeast across southeast MT and parts of the western Dakotas
   during the late afternoon and evening. While buoyancy will be
   limited to the west of a slow-moving cold/quasi-stationary front in
   the central Dakotas, the strong effective shear will support
   potential for longer-track supercells and fast-moving clusters
   capable of both severe hail and wind. A separate corridor of severe
   thunderstorms may initiate along the surface front in central ND
   during the evening as strengthening convergence along it finally
   erodes MLCIN due to the EML. Initial development in this corridor
   may briefly become supercellular before potentially merging into the
   fast-moving clusters from the west. 

   ...Mid-MO Valley to southern MN...
   An MCV over northeast NE should advance northeast into southern MN
   by peak heating, while an upstream low-amplitude mid-level trough
   over eastern CO approaches the Mid-MO Valley this evening. Guidance
   is fairly consistent in depicting potential for an extremely
   unstable air mass (MLCAPE of 4000+ J/kg) to develop across the
   Mid-MO Valley as surface dew points rise into at least the low 70s
   beneath very steep mid-level lapse rates. 

   Convection appears most probable with the lead MCV along the
   periphery of the EML/MLCAPE gradient, to the northeast of the
   surface warm front. An enlarged low-level hodograph would foster a
   risk for a few supercells and all hazards. However, unfavorable
   hodographs from the mid to upper-levels should generally support a
   predominant cluster mode. 

   Farther southwest, the stout EML should preclude open warm-sector
   storm development until early to mid evening once the low-level jet
   intensifies and mesoscale ascent tied to the eastern CO wave
   arrives. Adequate low to deep-layer shear given the strong to
   extreme buoyancy will also support a risk for all hazards into late
   evening. At least an isolated severe wind/hail risk should persist
   into the early overnight across parts of IA and southern MN prior to
   the low-level jet subsiding in the pre-dawn hours. 

   ...KY/TN to the Carolinas...
   Multiple clusters are ongoing across the Lower OH Valley and parts
   of KY tied to a minor mid-level impulse/remnant MCV. This feature
   should eject east-southeast into NC tonight. A belt of 30-40 kt
   700-mb westerlies will support potential for multiple organized
   clusters to evolve east-southeast as the air mass becomes moderately
   unstable to the south of morning convection. Scattered damaging
   winds will be the primary threat within this regime. 

   ...Upper DE Valley to southern New England...
   An upper low will gradually dampen as it moves south across Quebec.
   A belt of 30-35 kt 500-mb westerlies should persist this afternoon
   across parts of southern NY and PA into southern New England. As the
   air mass becomes modestly unstable with MLCAPE reaching 1000-1500
   J/kg, isolated to scattered thunderstorms are expected across the
   region. The setup should yield a risk for damaging winds and
   marginally severe hail.

   ..Grams/Gleason.. 06/28/2020

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