SPC Day 1 Convective Outlook — 06Z Forecast Discussion on 19 May 2024

712 ACUS01 KWNS 190558 SWODY1 SPC AC 190556 Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1256 AM CDT Sun May 19 2024 Valid 191200Z - 201200Z ...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS IN SOUTHWEST TO CENTRAL KS... ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS SEPARATELY IN EAST-CENTRAL TO SOUTHEAST FL... ...SUMMARY... Severe thunderstorms are expected across parts of Kansas into northwest Oklahoma from late afternoon into mid-evening, including the potential for a derecho. Destructive wind swaths of 80-100 mph may occur, with localized extreme gusts exceeding 100 mph possible. Very large hail and a few tornadoes are also anticipated. ...KS/OK vicinity... An active severe-weather day is expected during the late afternoon to mid-evening. Primary changes this outlook are to increase wind and hail probabilities with above-average guidance agreement regarding the likelihood of supercells evolving into multiple linear bows. Significant severe, from both hail and especially wind, appears likely. How far downstream higher-end intensity threats will persist towards the lower plains is more uncertain. General thunderstorm activity is expected to be ongoing within a low-level warm theta-e advection regime across parts of the central Great Plains. This will probably persist through much of the morning into the afternoon, becoming more centered on the Mid-MO Valley to Upper Midwest. Pronounced differential boundary-layer heating is expected between this early-day activity and full insolation that yields hot surface temperatures across the southern High Plains. With a plume of mid to upper 60s surface dew points overspreading much of western/central OK into central KS, beneath a plume of very steep mid-level lapse rates, a strongly unstable airmass will develop with MLCAPE of 2500-3500 J/kg becoming common. A strengthening upper-level jet across the Southwest, nosing over the southern Rockies, should aid in dryline sharpening by late afternoon. Initial very high-based thunderstorms should form off the Raton Mesa behind the dryline, while other storms form along the dryline near the TX Panhandle/western OK border, and in the north-central KS vicinity near the warm front. The far southern dryline storms in northwest OK and near the warm front in KS should remain semi-discrete longer, and will be most capable of producing very large hail and a couple tornadoes. Between these two corridors, CAM signals are fairly consistent that a mix of outflow-dominated clusters with embedded supercells will move east-northeast during the evening. This includes evolution into linear bowing segments with forecast soundings, indicating potential for intense rear-inflow jet development. Given the highly favorable thermodynamic environment, coupled with the impinging of a mid-level jetlet across the southern High Plains, this scenario appears probable. The southern to central Great Plains low-level jet will strengthen during the evening, which should result in a large MCS with embedded bowing structures persisting after dusk. CAM guidance is fairly quick to indicate diminishing intensity as MLCIN rapidly increases across much of OK into at least southeast KS. But given the potential for prolific, organized severe wind swaths upstream, have increased severe probabilities downstream from the Mid-MO Valley and deeper into OK. ...Western NE to western/central SD... Scattered thunderstorm development is expected along the northern portion of the dryline during the late afternoon to early evening as a narrow plume of mid to upper 50s surface dew points spreads north. With a more confined and more modestly buoyant warm-moist sector relative to KS southward, overall threat should consist of isolated to scattered large hail and severe wind. ...FL... Scattered afternoon thunderstorms appear likely to develop ahead of a slow-moving, positive-tilt shortwave trough over the Southeast. Best potential for a few supercells should be focused along the Atlantic Coast sea breeze across parts the central to south peninsula. Favorable deep-layer shear, in conjunction with large buoyancy, should foster a predominant threat of large hail, with isolated damaging winds possible as well. ..Grams/Bentley.. 05/19/2024 $$