SPC 1200Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1248 AM CDT Thu Oct 22 2020 Valid 221200Z - 231200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM A PORTION OF EASTERN IOWA INTO EXTREME SOUTHWEST WISCONSIN... ...SUMMARY... A few strong to severe storms capable of producing mainly hail and strong wind gusts, will be possible Thursday from the eastern Iowa vicinity into extreme southwest Wisconsin. ...Eastern Iowa into extreme southwest Wisconsin... An upper trough will amplify over the northern Plains and upper Midwest today. A warm front currently extends from southern KS through southern MO and IL. This feature will move northward during the day and should extend from a weak surface low in east-central IA to near the IL/WI border by late afternoon. This front will likely move into southern WI during the early evening. Concurrently, a cold front extending southwest from the surface low will surge southeast through the central and southern Plains and middle MS Valley regions this afternoon and evening. A moist warm sector with dewpoints in the low 60s F will advect northward into the Midwest region in wake of the warm front. A few cloud breaks may occur, and MLCAPE from 1000-1500 J/kg is possible just ahead of the cold front. Stronger deep-layer forcing associated with the upper trough will remain in post-frontal region, but storms will likely initiate along and just behind the front as it advances southeast during the day. Vertical wind profiles in vicinity of the cold front will be favorable for storm organization with 45 kt effective bulk shear and sizeable low-level hodographs, especially near triple point region as the weak surface low develops northeast. However, with upper flow remaining nearly parallel to the initiating boundary, tendency should be for storms to be undercut shortly after initiation. Nevertheless, activity developing along the cold front might become organized and capable of producing a few instances of large hail and damaging wind. While a brief tornado or cannot be ruled out, overall tornado threat should remain limited by tendency for storms to be forced behind the cold front. ...West Texas... A compact southern-stream shortwave trough evident on satellite imagery over AZ is embedded within weak flow aloft and will reach west TX by late afternoon, where it will interact with an evolving dryline. A few storms are expected to develop along this boundary by late afternoon across western TX where the atmosphere is expected to become moderately unstable. Though vertical shear should remain modest, steep lapse rates, inverted-V boundary layers and 1000-1500 j/kg MLCAPE will support some threat for a few locally strong wind gusts and hail, before activity weakens as it moves farther east into a stabilizing boundary layer by mid evening. ..Dial/Lyons.. 10/22/2020
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