SPC Day 1 Convective Outlook — 06Z Forecast Discussion on 25 May 2024

808 ACUS01 KWNS 250559 SWODY1 SPC AC 250558 Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1258 AM CDT Sat May 25 2024 Valid 251200Z - 261200Z ...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS IN PARTS OF KANSAS/OKLAHOMA AND FAR SOUTHWEST MISSOURI... ...SUMMARY... An outbreak of severe thunderstorms is forecast from late afternoon into tonight across parts of the central and southern Great Plains. A few long-lived supercells capable of intense tornadoes may occur. Giant hail and destructive wind gusts are also expected. ...Central and southern Great Plains... Much uncertainty plagues this outlook cycle, with the level 4-Moderate risk left as-is. This evening's guidance has trended slower and more confined with the boundary-layer moisture return, with most CAMs also suggesting earlier afternoon initiation occurring along the periphery of the richer moisture in west TX. Level 5-High risk potential remains evident with the 00Z HRRR indicating a possible tornado outbreak scenario with long-lived strong to violent tornadoes. Consensus of evening guidance suggests low-level moisture return will be within a confined swath emanating north from the south-central TX portion of the Rio Grande Valley into west TX. This will occur downstream of a modestly amplified mid-level trough, consisting of multiple embedded shortwave impulses, ejecting across the West into the central and southern High Plains. Surface temperatures west of the dryline will become hot, and most CAMs indicate early to mid-afternoon thunderstorm development in the TX Big Country/western north TX vicinity. It is probable that this will become the southern extent of the overall severe threat with slow-moving supercells persisting into the evening. Across OK/KS, richer and deeper boundary-layer moisture ahead of the dryline should be confined to western OK through late afternoon. A more well-mixed boundary layer is expected farther north in western/central KS, while the rich moisture should be shallow in central OK before deepening later. Most guidance suggests high-based thunderstorms will develop in the late afternoon across southwest NE and northwest KS, where mid-level cooling will be greatest. Very large hail and isolated severe wind gusts will be the primary threats during the afternoon with relatively elongated/straight hodographs supporting potential for left and right-splitting supercells. A strengthening low-level jet will aid in the tornado threat substantially increasing by early evening. The most volatile environment for long-lived, intense tornadic supercells should exist over the western half of OK. Primary uncertainty precluding an upgrade is the degree of impact earlier afternoon storms to the south may have on this setup with left-splits/outflows. The northern periphery of the richer/deeper moisture surge and robust low-level jet is eventually expected to reach at least into southern KS during the evening. Supercells in this region will strengthen as this occurs, and become capable of producing long-lived, intense tornadoes after dusk. But with time tonight, increasing large-scale ascent should support a supercell to bow echo to MCS evolution towards the Ozark Plateau vicinity. This should yield a swath of damaging winds, with embedded significant severe gusts and tornadoes possible as it tracks eastward along the MLCAPE gradient overnight. ...Eastern States... Three areas of level 1-MRGL risk are forecast today with sporadic severe hail and locally damaging winds possible. Remnant morning convection and attendant MCVs may aid in isolated severe across parts of the Deep South early, before spreading/developing east towards parts of the coastal Atlantic Southeast during the afternoon. Separately, a marginal supercell wind profile will also exist along the southeast FL sea breeze. Across the Lower Great Lakes to central/northern Appalachians, initial mid-level ridging will evolve to a flatter, zonal flow regime. The trailing surface front attendant to a nearly stationary, occluded cyclone along the southeast MB/northwest ON border area should aid in isolated to scattered thunderstorms this afternoon, some of which should become strong. ..Grams/Moore.. 05/25/2024 $$