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Tuesday, October 12, 2021

SPC Oct 12, 2021 1730 UTC Day 2 Convective Outlook

SPC 1730Z Day 2 Outlook Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 1220 PM CDT Tue Oct 12 2021 Valid 131200Z - 141200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FOR EASTERN SOUTH DAKOTA...MIDWEST AND WESTERN GREAT LAKES...SOUTH-CENTRAL TEXAS... ...SUMMARY... A marginal severe risk may develop Wednesday across portions of eastern South Dakota, the middle to upper Mississippi Valley and western Great Lakes, and portions of south-central Texas. ...Synopsis... A mid-level low will move northeastward from northern NE to southern Saskatchewan during the period as an intense speed max moves from the central Great Plains into the western Great Lakes. In the low levels, a surface low will develop northeast from southern SD into southern Saskatchewan while a trailing cold front sweeps east across much of the Midwest with the trailing portion of the boundary stalling over the southern Great Plains. ...Eastern SD vicinity... Elevated thunderstorms are possible Wednesday morning in association with strong deep-layer forcing for ascent. In wake of this early-day activity, strong mid-level cold air advection will result in weak instability developing within a narrow ribbon ahead of the surface boundary. A conditional, albeit plausible scenario is for convection to develop during the mid-late morning on the wind shift. Forecast soundings indicate a couple of the stronger updrafts --if they manage to develop-- will be capable of an isolated risk for severe before this activity moves north and weakens by midday. ...Midwest/western Great Lakes... Rather widespread early/ongoing precipitation across the Mid and Lower Missouri Valley will spread northeastward across the Upper Midwest and into the Upper Great Lakes through the period. This precipitation and associated cloud cover will limit destabilization potential across the MRGL risk area, i.e. near the triple point and into the warm sector of the occluded low. Still, sufficient shear for organized storms will be available, such that a few stronger storms/storm clusters evolving where pockets of modest destabilization occur could become locally/briefly severe. Have adjusted low-severe probabilities slightly westward where surface-based initiation may occur and to account for limited destabilization/severe potential on the eastern part of the MRGL risk. The risk for the stronger storms will be gusts and perhaps a tornado, primarily during the late afternoon through the evening hours. ...Parts of the Lower Rio Grande Valley into the Hill Country of southern Texas... Progression of a cold front across Texas early in the period will slow/become hindered with time, as remnants of tropical system Pamela (now over the eastern Pacific west of Mexico) shift across Mexico toward -- and eventually into -- southern Texas overnight. Deep-layer moisture increasing with time will keep lapse rates aloft weak, and thus CAPE limited, but increasingly favorable low-level shear with time may support a few stronger/rotating storms. A localized risk for a severe gust and perhaps a tornado will focus across south-central TX during the evening and overnight. ..Smith.. 10/12/2021 Read more LIVE: spc.noaa.gov