SPC 1200Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1249 AM CDT Sat Oct 09 2021 Valid 091200Z - 101200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM A PORTION OF THE NORTHERN PLAINS INTO THE UPPER MISSISSIPPI VALLEY... ...SUMMARY... Scattered strong/locally severe storms capable of mainly large hail and damaging wind but also a couple of tornadoes are expected over a portion of the northern Plains through the upper Mississippi Valley this afternoon into the evening hours. ...Northern Plains through the upper Mississippi Valley region... A stalled front currently extends from northwest MN southwestward through northeast and southwest SD. A shortwave trough now situated over the northern Rockies is forecast to continue east through the northern Plains this afternoon before reaching the upper MS Valley this evening. A surface low is forecast to develop across central or eastern SD later today in response to forcing for ascent attendant to the approaching shortwave trough. The low will subsequently move northeast along the front, reaching northwest MN during the evening. Partially modified Gulf air with low 60s F dewpoints will advect northwestward through the warm sector and beneath 7 C/km mid-level lapse rates. At least partial cloud breaks are expected with surface temperatures likely to warm through the 70s F contributing to 1000-1500 J/kg MLCAPE. Both low-level and deep-layer shear will increase during the day with the approach of an upper jet coupled with a strengthening low-level jet. Storms will likely increase in coverage along the northeast-southwest oriented front from central through northeast SD to southeast ND as the atmosphere destabilizes and as forcing for ascent increases. Effective bulk shear from 40-50 kt will support the potential for organized storms including a few supercells, but the overall tendency should be for storms to gradually evolve into line segments with embedded organized structures. Large hail and damaging wind will be the primary threats, but low-level hodographs with up to 250 m2/s2 storm relative helicity will also support the potential for a couple of tornadoes, especially with any embedded or discrete supercell structures. Primary threat should eventually transition to damaging wind as storms grow upscale. An upgrade to enhanced risk might be warranted in subsequent day 1 updates for a portion this area if it becomes apparent that boundary layer destabilization will become sufficient for a more robust severe threat. ..Dial/Elliott.. 10/09/2021 Read more LIVE: spc.noaa.gov
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