652 ACUS01 KWNS 162001 SWODY1 SPC AC 162000 Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0300 PM CDT Wed Jun 16 2021 Valid 162000Z - 171200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS PARTS OF THE UPPER MIDWEST AND SOUTH ATLANTIC COAST... ...SUMMARY... Isolated severe hail and damaging winds will be possible through early evening from north Florida to southern South Carolina, and mainly tonight across southern Minnesota into Iowa. ...Discussion... No appreciable change is needed to the previous convective outlook. ..Smith.. 06/16/2021 .PREV DISCUSSION... /ISSUED 1128 AM CDT Wed Jun 16 2021/ ...Upper Midwest... A shortwave trough moving east across the Prairie Provinces will aid in suppression of the mid-level ridge across the Upper Midwest to northern Ontario. A trailing cold front will advance east across the central and eastern Dakotas into western MN, arcing southwestward across northeast to southwest NE by tonight. Warm advection between 850-700 mb will likely maintain sufficient MLCIN to mitigate late afternoon storm development along the front, owing to a confined moderately rich boundary-layer moisture plume emanating north from the Ozarks to Mid-MO Valley. The one exception may be in the southeast SD vicinity where surface temperatures approaching 105 may be adequate to remove MLCIN. Here, a conditional risk exists for a high-based storm capable of severe wind and marginal hail. Otherwise, the main convective development should be driven by low-level warm/moist-advection tonight across parts of MN/IA along the periphery of the more stout EML farther west in the Great Plains. Cloud-layer shear should be relatively modest with a fairly uniform northwesterly flow regime lacking in appreciable strengthening of winds above 500 mb. This should result in a predominant cluster convective mode. Despite convection likely initially being rooted closer to 700 mb, the steep lapse rate environment above 850 mb should yield ample DCAPE, which may support a threat for strong to locally severe winds in addition to isolated severe hail overnight. Below-average confidence exists in the degree of overnight severe coverage, as well as its spatial location, mitigating an upgrade. ...FL/GA border to southern SC... Despite a reduction in potential peak MLCAPE today after yesterday's convective overturning, a plume of low 70s surface dew points persists to the south of a stalled surface front. This buoyancy reduction should be compensated by stronger deep-layer shear and ascent tied to a shortwave impulse approaching from the southern Appalachians. This renders enough concern for a few updrafts capable of producing isolated severe hail and locally damaging winds to warrant a cat 1/MRGL risk this afternoon into early evening. $$
