SPC Apr 18, 2025 0600 UTC Day 1 Convective Outlook
SPC 1200Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1235 AM CDT Fri Apr 18 2025 Valid 181200Z - 191200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM THE SOUTHERN PLAINS TO THE GREAT LAKES... ...SUMMARY... Scattered severe thunderstorms are possible from parts of the southern Plains northeastward toward the upper Great Lakes from late afternoon into early Saturday morning. Large hail and isolated severe gusts will be the main hazards, especially across the southern Plains where storms will be more concentrated. ...Discussion... Strong 500mb speed max is currently digging south across the northern Inter-Mountain Region. This feature will encourage a pronounced upper trough to evolve over the southwestern U.S. by the end of the period. A broad zone of strong mid-level flow will extend across northern Mexico-southern Plains-Great Lakes as height falls gradually spread into this corridor of the CONUS. As this trough deepens into lower latitudes, surface pressures will rise in the lee of the Rockies over the Plains, and a sharp cold font will surge into western IA-southern KS-OK Panhandle by the start of the period. This boundary will likely serve as a focus for robust convection through the period, and it should extend from eastern WI-western MO-northern TX Panhandle by early evening. Latest model guidance does not allow the upper Midwest/Great Lakes region to destabilize appreciably as buoyancy will be somewhat limited across this region. Even so, strong flow/shear warrant some concern for convective organization, and some risk for wind/hail will accompany frontal/pre-frontal storms as the boundary advances east through the period. Of more concern is the air mass across the southern Plains. Strong boundary-layer heating is expected across the High Plains from eastern NM into northwest TX, just south of the front. The northeast extent of this steep low-level lapse rate plume will likely extend into central OK. Latest model guidance suggests strong SBCAPE will evolve east of the dryline, and south of the front. As temperatures warm through the mid 80s convective temperatures will be breached along the dryline, likely by 21z. Forecast soundings support this and supercells are expected. This activity should grow upscale and spread northeast along the frontal zone. A considerably amount of post-frontal elevated convection is ultimately expected, and steep mid-level lapse rates favor hail with the elevated storms. While the frontal zone will prove sharp, with significant undercutting of updrafts, there is some risk for tornadoes prior to this occurring. Latest NAM guidance has 500mb temperature cooling to -15C at FSI by 04z, thus very large hail can be expected with supercells. Cold front will gradually sag southeast during the overnight hours, but an extended convective event is likely from western OK into the Mid-MS Valley due to the evolution of the longer-wave pattern. ..Darrow/Wendt.. 04/18/2025 Read more
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1235 AM CDT Fri Apr 18 2025 Valid 181200Z - 191200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM THE SOUTHERN PLAINS TO THE GREAT LAKES... ...SUMMARY... Scattered severe thunderstorms are possible from parts of the southern Plains northeastward toward the upper Great Lakes from late afternoon into early Saturday morning. Large hail and isolated severe gusts will be the main hazards, especially across the southern Plains where storms will be more concentrated. ...Discussion... Strong 500mb speed max is currently digging south across the northern Inter-Mountain Region. This feature will encourage a pronounced upper trough to evolve over the southwestern U.S. by the end of the period. A broad zone of strong mid-level flow will extend across northern Mexico-southern Plains-Great Lakes as height falls gradually spread into this corridor of the CONUS. As this trough deepens into lower latitudes, surface pressures will rise in the lee of the Rockies over the Plains, and a sharp cold font will surge into western IA-southern KS-OK Panhandle by the start of the period. This boundary will likely serve as a focus for robust convection through the period, and it should extend from eastern WI-western MO-northern TX Panhandle by early evening. Latest model guidance does not allow the upper Midwest/Great Lakes region to destabilize appreciably as buoyancy will be somewhat limited across this region. Even so, strong flow/shear warrant some concern for convective organization, and some risk for wind/hail will accompany frontal/pre-frontal storms as the boundary advances east through the period. Of more concern is the air mass across the southern Plains. Strong boundary-layer heating is expected across the High Plains from eastern NM into northwest TX, just south of the front. The northeast extent of this steep low-level lapse rate plume will likely extend into central OK. Latest model guidance suggests strong SBCAPE will evolve east of the dryline, and south of the front. As temperatures warm through the mid 80s convective temperatures will be breached along the dryline, likely by 21z. Forecast soundings support this and supercells are expected. This activity should grow upscale and spread northeast along the frontal zone. A considerably amount of post-frontal elevated convection is ultimately expected, and steep mid-level lapse rates favor hail with the elevated storms. While the frontal zone will prove sharp, with significant undercutting of updrafts, there is some risk for tornadoes prior to this occurring. Latest NAM guidance has 500mb temperature cooling to -15C at FSI by 04z, thus very large hail can be expected with supercells. Cold front will gradually sag southeast during the overnight hours, but an extended convective event is likely from western OK into the Mid-MS Valley due to the evolution of the longer-wave pattern. ..Darrow/Wendt.. 04/18/2025 Read more
