SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0243 PM CDT Mon Oct 12 2020 Valid 122000Z - 131200Z ...NO SEVERE THUNDERSTORM AREAS FORECAST... ...SUMMARY... Organized severe thunderstorms are not expected through tonight. ...20Z Update... A strongly forced band of convection continues to move eastward just ahead of the leading edge of the cold front northern and central portions of Lower MI. Regional surface observations have yet to measure any substantial gusts within this band, evidence of its elevated character, which will continue to limit any severe potential across the Upper Great Lakes. Farther south and east, less stable low levels may result in a few, convectively enhanced gusts at the surface. However, the stronger flow and forcing for ascent will remain displaced north of the modest instability across the OH Valley, keeping the overall potential for wind gusts over 50 kt low. ..Mosier.. 10/12/2020 .PREV DISCUSSION... /ISSUED 1101 AM CDT Mon Oct 12 2020/ ...Great Lakes and OH Valley through this evening... Within a largely zonal flow regime, a midlevel shortwave trough will move eastward from the upper MS Valley to the Great Lakes/OH Valley while gradually losing amplitude, as an upstream speed max progresses eastward from the northern Rockies to the northern Plains. Elevated convection is ongoing across WI in the zone of ascent along a surface cold front and immediately downstream from the midlevel trough, where lingering midlevel lapse rates near 8 C/km and MUCAPE of 500-1000 J/kg will support isolated, sub-severe hail through midday. This regime will shift eastward over MI this afternoon, though diminishing buoyancy aloft with eastward extent suggests that the severe threat is minimal. Farther south, low-level moisture advection in advance of the cold front, as well as modest surface heating in cloud breaks beneath a narrow plume of 7-8 C/km midlevel lapse rates, will support MLCAPE of 250-500 J/kg this afternoon/evening across the OH Valley. However, low-level flow will not be particularly strong (30 kt or less), and the potential for strong/damaging gusts with shallow frontal convection appears too low to warrant an outlook area.
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