Severe Storm Outlook Narrative (AC)
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Issued by NWS
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118 ACUS01 KWNS 240554 SWODY1 SPC AC 240552 Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1252 AM CDT Fri May 24 2024 Valid 241200Z - 251200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS IN PARTS OF THE MIDWEST TO THE MID-SOUTH AND SOUTHERN GREAT PLAINS... ...SUMMARY... Scattered severe thunderstorms will be possible from parts of the Midwest to the Mid-South and southern Great Plains, mainly this afternoon and evening. Greatest potential for a few tornadoes exists across central to northern Illinois, far eastern Iowa, and southern Wisconsin. ...Upper MS Valley to the Mid-South and southern Great Plains... An MCS will be ongoing at 12Z, likely approaching the Upper MS Valley. 00Z CAM guidance runs the gamut on the evolution of this MCS through late morning into midday. Some suggest it will weaken as it outpaces the instability axis lagging to its southwest over the Lower MO Valley to the southern Great Plains. Others indicate that the southern flank of the MCS may intensify across the Mid-MS Valley into IL, as diurnal destabilization ensues along the instability gradient. Thus, large-scale outflow boundary placement varies considerably by afternoon from far southern WI to far southern MO. The surface cyclone over southeast ND will curl north-northeast into southeast MB and occlude, as it becomes vertically stacked beneath its attendant mid-level low. Daytime mid-level height falls, coincident with stronger low-level shear, will be most pronounced over the Upper MS Valley. These will be weaker with southward extent over the Mid-MS Valley. A predominately zonal mid-level flow regime is expected farther south with minimal height change. However, low-level convergence should be adequate for isolated to scattered thunderstorm development along the trailing cold front from the Upper MS Valley to eastern OK and the dryline into central TX. While the more favorable low-level shear and ascent will be focused north, aforementioned uncertainties over the degree of destabilization related to the evolution of the morning MCS preclude a greater categorical risk. Conditionally, the remnant outflow boundary will likely provide a focus for greater supercell tornado potential. Primary change this outlook is to expand both the 2 percent tornado probability north in WI and the 5 percent prob south in IL. Very large buoyancy is expected from the Ozark Plateau southward with MLCAPE of 3500-4500 J/kg. Despite the lack of appreciable large-scale ascent beyond the front/dryline, this degree of instability, coupled with pronounced mid to upper-level speed shear, should favor potential for very large hail with initial supercell development. Given the frontal forcing, a few clusters may evolve downstream during the evening across parts of the Mid-South to central TX with a mixed large-hail and damaging-wind threat. ...GA to the Carolinas... A parade of MCVs moving eastward across the southern states will aid in isolated-scattered afternoon to early evening thunderstorms. While instability will not be as large as farther west over the Mid-South to southern Great Plains, it will be sufficient to warrant sporadic occurrences of severe hail and damaging winds eastward to the coastal Carolinas. ..Grams.. 05/24/2024 $$