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Sunday, August 8, 2021

SPC Aug 8, 2021 1630 UTC Day 1 Convective Outlook

SPC 1630Z Day 1 Outlook Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1124 AM CDT Sun Aug 08 2021 Valid 081630Z - 091200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS THIS AFTERNOON INTO TONIGHT FROM WI TO THE OZARK PLATEAU... ...SUMMARY... Severe thunderstorms with damaging winds and large hail are possible mainly this afternoon and evening from Wisconsin and Iowa southward to the Ozark Plateau. Isolated severe winds are also possible across portions of Montana. ...Central/northeast WI this afternoon/evening... A surface warm front will move slowly northward across central WI today, in advance of the primary midlevel trough over IA. Boundary-layer dewpoints near 70 F and surface temperatures warming into the 80s in cloud breaks will boost MLCAPE to near 2000 J/kg this afternoon along and south of the warm front. Thunderstorm development is expected by early afternoon along the front in southwest WI, and storms will spread northeastward through this evening. The presence of moderate-strong buoyancy and effective bulk shear of 25-35 kt will support somewhat organized storm clusters, and perhaps an embedded supercell or two, capable of producing damaging outflow winds and isolated large hail from mid to late afternoon. ...Central MO to western IL this afternoon/evening... Embedded perturbations will continue to rotate eastward from eastern KS across MO, through the base of the primary midlevel trough over IA. Weak remnant convective outflow and differential heating along the leading edge of the more persistent clouds should support thunderstorm development by early afternoon across central MO. Though vertical shear will remain rather modest (roughly 25 kt effective bulk shear) and supportive of multicell clusters, MLCAPE of 2000-3000 J/kg and DCAPE over 1000 J/kg will favor occasional large hail of 1 to 1.5 inch diameter and damaging outflow gusts near 60 mph as storms spread eastward/northeastward from MO into IL through the afternoon/evening. ...MO to eastern KS/northeast OK tonight... In the wake of the afternoon convection across central MO, warm advection will be sustained into tonight by a 30-40 kt southwesterly low-level jet. The warm advection, and any lingering outflow boundaries, will help focus thunderstorm development into the overnight hours. Deep-layer vertical shear and low-level hodograph curvature will favor some embedded supercell structures in a broader zone of convection, and the stronger storms will be capable of producing occasional large hail/damaging winds, and an isolated tornado may also occur (if a surface-based storm can form and move along a remnant outflow boundary from prior convection). ...MN/IA border this afternoon/evening... A long-lived MCV (now over southwestern MN) will continue to move slowly east-southeastward over southern MN/northern IA this afternoon/evening. Boundary-layer dewpoints in the 65-70 F range and pockets of surface heating should support the development of another thunderstorm cluster with the MCV this afternoon/evening near the MN/IA border. Moderate buoyancy and some enhancement of low-midlevel vertical shear will support a mix of multicell clusters and low-end supercells capable of producing isolated damaging outflow gusts and large hail. ...Montana this afternoon through late evening... A pronounced midlevel trough over WA will progress eastward to the ID Panhandle and western MT by this evening. The midlevel trough will be preceded by a surface cold front moving southeastward across central MT today. Though low-midlevel moisture is somewhat limited in the warm sector, some high-based convection is expected near the cold front this afternoon through late evening. Though buoyancy will remain weak, deep inverted-v profiles and increasing midlevel flow suggest that the strongest storms could produce a few outflow gusts near 60 mph. ..Thompson/Bentley.. 08/08/2021 Read more LIVE: spc.noaa.gov