SPC 1630Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1054 AM CDT Wed Sep 21 2022 Valid 211630Z - 221200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS LOWER GREAT LAKES...UPPER OHIO VALLEY...AND THE NORTHEAST GREAT BASIN... ...SUMMARY... Scattered thunderstorms capable of severe hail, damaging winds, and a couple of tornadoes are expected into this 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 northeast Great Basin this afternoon. ...Lower Great Lakes/Upper OH Valley... Clusters of elevated strong storms are ongoing across southeast Lower MI into southwest ON within a corridor of 850-700 mb warm theta-e advection and leading mid-level height falls attendant to a positive-tilt shortwave trough centered on northern ON. Consensus of 12Z CAM guidance, including recent HRRR runs, have failed to simulate this activity. The HRW-NSSL and NAM-Nest have some semblance of these storms and appear reasonable with indicating movement to the southeast downstream of the Lake Erie area through the afternoon. Steep mid-level lapse rates sampled by the 12Z DTX sounding are already in place downstream with an EML expected to spread at least into western portions of PA/NY. These elevated clusters should build into the destabilizing boundary layer, especially across northern OH given warmer and more moist conditions advecting from the west. It's plausible that clusters may still hold onto a slightly elevated character with eastern extent in NY/PA owing to the lack of surface-based instability at this time and relatively early convective evolution for the main severe scenario. This setup suggests the primary severe threats will be large hail and damaging winds. The tornado threat is more uncertain and will likely be confined to a corridor within the surface-based instability gradient where low-level hodographs can remain enlarged and semi-discrete supercell structures can develop within the southeast-moving clusters. This still appears most probable in the eastern OH/western PA vicinity later this afternoon. ...Eastern/northern Great Basin and the Interior West... A deep mid/upper trough centered on the northern CA vicinity will pivot northeast into the Interior Northwest through tonight. Broad large-scale ascent ahead of this trough in conjunction with the northern extent of a Gulf of CA moisture plume should aid in an arc of thunderstorm development this afternoon from western UT across southern ID. While buoyancy will be scant with northern extent, elongated mid to upper-level hodographs will favor potential for a few supercells with mid-level rotation, focused on northwest UT to south-central ID. Strong to isolated severe wind gusts along with isolated/marginally severe hail are the expected hazards. Regenerative convection will likely persist this evening into tonight but the overall severe threat will diminish with onset of nocturnal surface cooling. ..Grams/Lyons.. 09/21/2022
