Severe Storm Outlook Narrative (AC)
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Issued by NWS
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303 ACUS01 KWNS 241945 SWODY1 SPC AC 241944 Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0244 PM CDT Tue Sep 24 2024 Valid 242000Z - 251200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FOR PARTS OF THE OHIO/TENNESSEE VALLEYS AND CENTRAL OKLAHOMA... ...SUMMARY... Isolated to scattered severe thunderstorms remain possible through the afternoon across portions of the Ohio and Tennessee Valleys into the central/southern Appalachians. Severe storms will also be possible across portions of Oklahoma this evening. ...20Z Update... Severe probabilities were trimmed slightly eastward across portions of the OH and TN Valleys, where the surface trough/wind shift has passed by, reducing low-level convergence. Otherwise, multiple bands of multicells and transient supercells will continue to pose a threat for mainly damaging gusts through the evening, with a couple instances of severe hail or even a tornado possible. Despite the presence of mid-level clouds and lowering of surface dewpoints over central OK, adequate boundary-layer heating is contributing to continued destabilization, with 19Z mesoanalysis already showing over 1000 J/kg MLCAPE in place. Continued surface heating should support multicell/supercell development over the next few hours, with severe hail and wind gusts the main concerns. ..Squitieri.. 09/24/2024 .PREV DISCUSSION... /ISSUED 1145 AM CDT Tue Sep 24 2024/ ...Ohio and Tennessee Valleys to southern Appalachians... Have spatially adjusted/expanded the Slight Risk based on observational trends and somewhat stronger destabilization across areas such as northern/middle Tennessee. Water-vapor imagery shows a mid-level vorticity maximum moving across the middle Mississippi Valley and into the Ohio Valley. A belt of moderate to strong southwesterly 500-mb flow (25-50 kt) will overspread Kentucky and the surrounding states. A surface low will migrate east-northeast into southern Lower Michigan by early evening, where isolated severe storms are possible, with a frontal zone extending south-southwest from this low into the Mid South. In the wake of early morning convection, modest cloud breaks/destabilization is forecast with upwards of 750-2000 J/kg MLCAPE from the southern Great Lakes into the southern Appalachians, with the strongest destabilization expected across Tennessee into southern Kentucky and possibly the western Carolinas pending the timing/abatement of lingering cloud cover. Regionally, ample deep-layer speed shear will aid in storm organization into organized multicells and probably several supercells. Damaging winds will be the most common hazard, but isolated large hail will be possible, and some tornado risk may exist as well. ...Oklahoma/North Texas... Have upgraded portions of central Oklahoma for what is expected to be a semi-focused regional corridor of large hail potential late this afternoon and early evening. The region will be influenced by the immediate backside of a southeastward-moving upper-level trough centered over the Lower Missouri Valley. A considerably strengthening cyclonically curved belt of westerlies aloft will influence Oklahoma, overspreading a relatively moist air mass, with lower to some middle 60s F surface dewpoints likely to persist through the diurnal heating/mixing cycle. Near a deepening surface low and nearby triple point/warm front, at least isolated storms are expected to develop as early as mid-afternoon (3-4pm), becoming more probable with a greater coverage through sunset. Overall buoyancy will not be robust, with MLCAPE generally not expected to exceed 1000 J/kg later this afternoon. However, this buoyancy, along with steep lapse rates and robustly vertically veering wind profiles, accentuated by 35-45 kt northwesterly mid/upper-level flow, should support initial supercells capable of large hail (potentially golfball size), along with some potential for damaging wind gusts. These storms will persist generally southeastward through the evening into southern/southeast Oklahoma, and probably north Texas overnight. Overall intensity will tend to wane nocturnally after sunset, but some severe hail/wind potential will probably linger, particularly on the west/southwest flank of any evolving clusters of storms, which will be increasingly elevated to the east of the warm front. $$