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Tuesday, October 12, 2021

SPC Oct 12, 2021 0600 UTC Day 1 Convective Outlook

SPC 1200Z Day 1 Outlook Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1243 AM CDT Tue Oct 12 2021 Valid 121200Z - 131200Z ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS THE CENTRAL AND SOUTHERN PLAINS... ...SUMMARY... Severe thunderstorms are expected this evening/overnight across portions of the central and southern Plains, where an all-hazards severe risk is anticipated. ...Central/Southern Plains... Early-morning water-vapor imagery depicts a well-defined upper trough beginning to advance east across the lower CO River Valley. This feature will eject northeast soon as a strong 500mb speed max translates through the base of the trough across NM into southeast CO by 13/00z, then into eastern NE by the end of the period. Strong 12hr mid-level height falls will precede this negative-tilt trough and large-scale forcing for ascent should overspread the High Plains by late afternoon. In response to this short wave, LLJ is beginning to strengthen across the High Plains but will shift a bit eastward across western OK-KS-NE-SD prior to convective initiation. Boundary-layer moisture has yet to move appreciably inland over the Coastal Plain of TX, with the leading edge of maritime-tropical air mass having advanced to COT-VCT (70F Td) at 05z. Water-vapor imagery depicts a weak disturbance over northeast Mexico ejecting northeast toward this region and this feature should encourage moisture to begin surging inland later today. Even so, higher-quality moisture should struggle to advance farther north than the eastern TX Panhandle/western OK prior to sunset; though further advection is expected into western KS during the evening. This delayed moisture return should negate more robust surface-based updrafts prior to sunset across the central High Plains, but severe thunderstorms will develop ahead of the trough during the evening as moisture surges north toward the lee cyclone. The Mexican short wave and low-level warm advection should aid early-day convection from the TX Hill country, north into OK. This activity should stay mostly sub-severe and the primary concern will be thunderstorms that initiate across the High Plains, just east of the strongest heating after 22z. Latest HREF suggests strong forcing will lead to convective initiation across the central Plains first, then more isolated activity should develop over the eastern TX Panhandle just before sunset. This southern activity will develop within a more moist/unstable environment, supporting very large hail. Have added sig hail to this portion of the outlook. Otherwise, a few tornadoes can be expected with supercells, especially this evening. Then, damaging winds are likely as a squall line should mature along the front due to strong forcing. Convection will spread east of I-35 as far south as OK by the end of the period. ..Darrow/Dean.. 10/12/2021 Read more LIVE: spc.noaa.gov
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