Severe Storm Outlook Narrative (AC)
Issued by NWS
Issued by NWS
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007 ACUS01 KWNS 210551 SWODY1 SPC AC 210550 Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1250 AM CDT Sat Sep 21 2024 Valid 211200Z - 221200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS THE SOUTHERN HIGH PLAINS... ...SUMMARY... Scattered severe storms are expected this afternoon and evening across the southern High Plains. Isolated strong to severe thunderstorms are also possible from the mid Missouri Valley to the Upper Midwest, and also from western Pennsylvania into northern/central Virginia. ...Southern High Plains... Notable upper trough has advanced into the lower CO River Valley early this morning. Strong 500mb speed max will soon round the base of the trough and eject across southern AZ into southern NM by late afternoon. This feature will greatly influence convective development/intensity across the southern High Plains by peak heating. Northern-stream short-wave trough will shift east today which will allow a sharp surface cold front to surge south across the High Plains into eastern CO by early afternoon, likely arcing across the northern TX Panhandle into northeast NM by 22/00z. Strong boundary-layer heating is expected across southern NM with more modest warming forecast within southeasterly upslope flow from the TX/NM border into the Sangre de Cristo range, just southwest of the cold front. Forecast soundings suggest convective temperatures will be breached fairly early, aided in part by frontal/orographic influences. Scattered convection will easily develop ahead of the short wave, and this activity will be strongly sheared as the speed max approaches. Supercells are expected to evolve within this environment as 0-6km shear will be on the order of 50kt, along with veering winds with height. Large hail should develop with this activity along with some risk for a few tornadoes. ...Upper Midwest to Mid MO Valley... Northern-stream short-wave trough is progressing across SK/eastern MT into the northern Plains, in line with latest model guidance. This feature is forecast to suppress the height field immediately downstream across eastern ND into northern MN, though the strongest falls will remain north of the international border. Even so, notable surface front will advance into MN-western IA-southern NE by 18z, then steadily surge east into the early evening hours. This boundary will serve as the focus for potential convective development during the late afternoon, though surface heating is not expected to be particularly strong ahead of the wind shift. With the strongest forcing expected to spread across northwest ON, convection may be more isolated along the front trailing across the Upper Midwest. Even so, some hail/wind threat will exist with this activity which should peak in intensity during the early evening. ...Western PA into western VA... Weak short-wave trough will dig southeast across the upper OH Valley later this afternoon with modest mid-level northwesterly flow expected to extend across western PA/VA. This feature will encourage scattered convection later this afternoon along a frontal zone that will be draped across the Delmarva-western PA into western NY. Convection that evolves near this wind shift will move southeast with an attendant risk for gusty winds and some hail. ..Darrow/Thornton.. 09/21/2024 $$