SPC AC 290556

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1256 AM CDT Sat Aug 29 2020

   Valid 291200Z - 301200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM THE MID
   ATLANTIC INTO PORTIONS OF NEW ENGLAND AND FOR EASTERN OK...AR...AND
   ADJACENT PORTIONS OF SOUTHEAST KS/SOUTHERN MO...

   ...SUMMARY...
   Severe storms are possible for parts of eastern Oklahoma into
   Arkansas this afternoon and evening, with damaging winds and large
   hail the main threats. A few strong to severe storms will also be
   possible from portions of the Carolinas into the Mid Atlantic and
   New England during the day, with damaging winds and perhaps a couple
   of tornadoes possible.

   ...Synopsis...
   An upper trough over the upper Great Lakes this morning will amplify
   and move into the Northeast by tonight, as a surface cyclone deepens
   and moves across northern New England. In advance of the large-scale
   trough, the surface-to-midlevel trough associated with the remnant
   of Laura will continue to weaken and move quickly offshore by early
   afternoon. Further west, an MCV is forecast to move from Kansas into
   the Ozark Plateau, while another upper trough begins to amplify over
   the Northwest. 

   ...Carolinas into New England...
   Clouds and precipitation will likely be widespread at the start of
   the period this morning from the Carolinas into New England.
   However, there will be some potential for modest
   heating/destabilization for near-coastal regions of the Mid Atlantic
   into the Carolinas, to the east of the more widespread morning
   convection. Enhanced low/midlevel flow associated with the 
   combination of Laura's remnant and the larger-scale upper trough to
   the northwest will favor a risk of locally damaging wind and perhaps
   a tornado or two from late morning into the afternoon, should any
   appreciable destabilization occur prior to convection moving into
   the region.

   Further north, in the wake of early convection, scattered
   thunderstorm development along the advancing front will be possible
   from central NY eastward into New England. Increasing midlevel flow
   and deep-layer shear will support organized convection, with a
   threat of locally damaging wind and perhaps some marginally severe
   hail with the strongest cells. 

   ...Oklahoma into Arkansas/southern MO...
   A cold front is expected to advance southward today across southern
   MO into portions of OK/AR. An MCV is forecast to move eastward to
   the north of the front across southern KS into MO, as a weak surface
   low develops along the boundary in the vicinity of the Red River.
   Substantial heating and rich low-level moisture will contribute to
   strong destabilization, with MLCAPE of 2500+ J/kg expected by
   afternoon near/south of the boundary and east of the surface low.
   This instability combined with effective shear of 25-35 kt will
   support a conditional threat of organized severe thunderstorms. 

   Evolution of convection remains somewhat uncertain across this
   region. Overnight convection may persist and intensify this morning
   into early afternoon just north of the boundary, with additional
   more discrete development possible late this afternoon near/east of
   the surface low and in the vicinity of the front and/or any outflow
   boundaries across the area. Storm coverage will likely increase this
   evening within a warm-advection regime as a southwesterly low-level
   jet develops, with eventual evolution into one or more
   upscale-growing clusters. Hail and locally damaging wind will be a
   threat with any semi-discrete storms. A somewhat greater coverage of
   damaging wind will be possible with any organized cluster. 

   ...High Plains...
   Widely scattered strong thunderstorms are possible this
   afternoon/evening across portions of the central/southern High
   Plains, within a post-frontal upslope-flow regime. Moderate
   instability and sufficient deep-layer shear will support a few
   organized storms with a corresponding risk of hail and locally
   severe wind gusts. 

   Further north, modest low-level moisture will advect northward into
   portions of WY/western SD and the NE Panhandle, to the east of a
   developing lee trough. A few strong storms may develop over the
   higher terrain and spread eastward, with a corresponding risk of
   isolated severe hail/wind.

   ..Dean/Jirak.. 08/29/2020

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