SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0800 AM CDT Wed Sep 21 2022 Valid 211300Z - 221200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS THE LOWER GREAT LAKES/UPPER OHIO VALLEY AND GREAT BASIN/INTERIOR WEST... ...SUMMARY... Scattered thunderstorms capable of severe hail, damaging winds, and a couple of tornadoes are expected this afternoon and evening across the Upper Ohio River Valley and the Lower Great Lakes. Isolated to scattered severe wind gusts are also possible across portions of the Great Basin this afternoon. ...Lower Great Lakes/Upper Ohio River Valley... Ahead of a southeastward-moving cold front, multiple clusters/bands of storms are ongoing early today across Lower Michigan as well as northern Indiana. This activity is likely aided by DPVA and warm/moist advection coincident with the leading edge of an east/northeastward-advecting elevated mixed plume as per 12z upper-air data. A few severe storms are possible this morning particularly across Lower Michigan with severe hail the main severe possibility. For additional short-term details, see Mesoscale Discussion 1810. West-southwesterly low-level winds will otherwise continue to advect a warm/moist air mass into the region with upper 60s/around 70 F surface dewpoints becoming increasingly established ahead of the progressive cold front. Coincident with steepening mid-level lapse rates, buoyancy is expected to reach around 2000 J/kg MLCAPE this afternoon along/ahead of the front from Ohio into western Pennsylvania, while decreasing with northeastward extent into New York/Vermont. Increasingly strong westerly winds in the 850-700 mb layer (30-45 kt) will elongate low/mid-level hodographs particularly across northern Ohio into western portions of Pennsylvania and New York. Some initial supercells capable of severe hail are possible as storms increase and intensify this afternoon, but upscale growth into linear segments will occur over time. Damaging winds should be most common, but a couple of tornadoes could also occur aside from wind/hail. ...Great Basin/Interior West... Deep-layer flow is expected to increase through the day across Utah into Idaho as the closed low moves east into the region. Ascent ahead of the wave coupled with increasing difluence should support a broad region of ascent with elongated hodographs featuring 0-6 km bulk shear near 50-60 kt. Moisture will likely advect to the north/northwest as low to mid-level flow becomes more meridional, supporting increasing buoyancy through the late afternoon. The degree of destabilization remains somewhat uncertain with some spread in guidance noted. Regardless, the strong kinematics/lift should support organization of discrete/semi-discrete cells. Strong to severe gusts will be possible, especially if/where morning cloud cover remains limited and supports greater insolation/steeper low-level lapse rates this afternoon. ..Guyer/Leitman.. 09/21/2022
