Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1237 AM CDT Sat Apr 29 2017 Valid 291200Z - 301200Z ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS FROM CENTRAL TEXAS TO SOUTHERN MISSOURI... ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM SOUTH CENTRAL TEXAS TO SOUTHWEST OHIO... ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM SOUTH TEXAS TO THE NORTHERN MIDDLE ATLANTIC... ...SUMMARY... Severe thunderstorms are expected from parts of south central Texas northeastward to portions of the Ohio Valley/northern Middle Atlantic region Saturday into Saturday night. These storms will be capable of large hail, damaging winds, and a few tornadoes. ...Discussion... Early-morning water vapor imagery depicts a well-defined upper low near the 4-Corners region, drifting slowly southeast in line with the latest model guidance. This feature is forecast to shift into the southern High Plains region by the end of the day1 period as strongest mid-level flow finally rotates through the base of the trough into northwest TX/western OK. Given this scenario, strongest mid-level height falls will not spread into west TX until late afternoon. As a result, large-scale forcing, for ascent, will be negligible across much of the warm sector through the period. It appears widespread convection will concentrate along a stationary frontal zone oriented from eastern OK into the OH valley and along the cold front as it surges eastward across OK/TX then into the lower MS Valley Saturday night. At 29/05z...a narrow corridor of widespread thunderstorms has evolved along the aforementioned frontal zone from northern OK, northeast into southern OH. Warm advection should maintain this zone of convection through sunrise Saturday morning. Hail may be the greatest severe risk with this activity, though very heavy rain may ultimately become an issue along this front as training thunderstorms allow the surface boundary to oscillate a bit through the period. By 12z Saturday, strong/severe squall line is expected to evolve along the cold front as it surges across OK/northwest TX. Damaging winds could evolve with this activity, in addition to some hail threat. Given the slow eastward movement of the upper low, and the lack of meaningful forcing across the warm sector, linear convection should be the primary storm mode along the cold front, though strong shear profiles do favor sustained rotating updrafts, especially immediately ahead of the surface low/warm front. Even so, warm frontal convection may struggle to maintain supercell characteristics across the mid MS Valley due to extensive precipitation/storm mergers. It appears an extensive frontal MCS will advance across the southern Plains into the mid/lower MS Valley region during the latter half of the period. Large hail and damaging winds are the primary threats, though a few tornadoes can not be ruled out if embedded supercells evolve along the squall line, or warm front. ..Darrow/Cohen.. 04/29/2017Read more
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