SPC 1630Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1127 AM CDT Tue Aug 10 2021 Valid 101630Z - 111200Z ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS THIS AFTERNOON INTO EARLY TONIGHT FOR EASTERN IA...NORTHERN IL...AND SOUTHERN WI... ...SUMMARY... Severe thunderstorms capable of wind damage and isolated large hail will be possible across a broad portion of the Midwest and Great Lakes region, especially this afternoon and evening. Locally severe wind gusts will also be possible in parts of the Ohio Valley and central Appalachians/Northeast States. ...Parts of the upper/middle MS Valley through tonight... A complex scenario is expected today, with corresponding predictability concerns. On the larger scale, a midlevel shortwave trough will eject east-northeastward over northern MN today, as an upstream trough digs southeastward over SK/MB. A surface front/wind shift associated with the ejecting trough will move eastward/southeastward across MN/IA before stalling late today. Farther south, a convectively-enhanced midlevel trough approaching southwest IA will continue eastward today, and a loosely organized cluster of storms is ongoing along I-70 in MO. It is possible that outflow with this cluster will be the impetus for more intense convection this afternoon farther east in northeast MO/west central IL, as well as with the convectively-enhanced wave interacting with the stalling front later this afternoon toward northeast IA. A reservoir of large buoyancy (MUCAPE greater than 4000 J/kg) is present across the Corn Belt per 12z soundings, based on 7.5-9 C/km midlevel lapse rates and lowest 100-mb mean mixing ratios of 17-19 g/kg (near-surface dewpoints in the mid-upper 70s). Given the aforementioned possibilities of more than one storm cluster and the area of large to extreme CAPE, have expanded the higher damaging wind probabilities farther south into MO/IL. Lapse rate profiles will favor both intense updrafts and downdrafts, with the potential for a swath or two of damaging winds (possibly up to 75-80 mph), though rather modest vertical shear casts some doubt on the organization and longevity of any storm clusters. ...Eastern OH/PA/NY this afternoon/evening... A midlevel trough with embedded perturbations will continue eastward today from the lower Great Lakes toward PA/NY. Convection is ongoing in a band across east central OH, where there is some potential for a few damaging outflow gusts in the short term. However, the storms are moving toward and area of weaker buoyancy, which casts doubt on the damaging-wind potential through the afternoon (refer to MD 1459 for additional details). Otherwise, a few loosely organized storm clusters/bands are expected in advance of these embedded perturbations into NY/PA, where MLCAPE near 1000 J/kg and a modest increase in flow/shear in the 850-500 mb layer will support multicell clusters capable of producing isolated wind damage. ..Thompson/Bentley.. 08/10/2021 Read more LIVE: spc.noaa.gov
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