Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1248 AM CDT Wed Apr 26 2017 Valid 261200Z - 271200Z ...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS ACROSS THE ARKLATEX REGION... ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS FROM NORTHEAST TEXAS TO EXTREME SOUTHERN MISSOURI... ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM SOUTHERN LOUISIANA TO SOUTHEAST MISSOURI... ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM THE UPPER TEXAS COAST TO NORTHWEST INDIANA... ...SUMMARY... Severe thunderstorms are expected across the Lower Mississippi Valley Wednesday. Tornadoes, large hail, and damaging winds should focus from northeast Texas across southern Arkansas and northern Louisiana primarily during the afternoon hours. Isolated severe thunderstorms may extend as far north as Illinois and into the central Gulf States during the overnight hours. ...Lower MS Valley... Early-morning water vapor/radar imagery depict a well defined upper circulation over northeast NM shifting east-southeast in line with late-evening model guidance. High-level flow is increasing across the southern Rockies and 500mb speeds on the order of 75kt will translate into central TX later today. This feature will induce significant mid-level height falls across the lower MS Valley and encourage strengthening LLJ over LA/AR by 18z. 26/00z observed soundings across TX depict very steep mid-level lapse rates, on the order of 8.5-9 c/km, and this lapse-rate plume should spread across the Arklatex region prior to convective development. Current thinking is thunderstorms will struggle to develop across much of TX due to significant CINH and this should allow air mass to destabilize across the MDT risk region as surface temperatures warm to near 80F with near 70F dew points. Forecast NAM soundings by early afternoon depict SBCAPE in excess of 3000 J/kg across northeast TX where convection should initiate prior to frontal passage. Shear profiles strongly favor supercells, though mid-level height falls and slightly backed mid-level flow could eventually lead to a more complex MCS as the trough ejects toward the Mid-south after dark. Very large hail could accompany the supercells across the Arklatex region and tornadoes appear possible. Strong/severe convection should spread into the central Gulf States during the evening/overnight hours as entrance region of upper jet shifts into this region during the latter half of the period. ...Mid MS Valley... Southwest-northeast oriented squall line has evolved from eastern OK into southwest MO early this morning. Models suggest this activity should be ongoing at the beginning of the period but possibly a bit farther east than deterministic data would suggest. This early-day convection will certainly disrupt and overturn buoyancy across much of the mid Mississippi Valley. It's not entirely clear how unstable MO/IL region will be ahead of this activity and forecast soundings suggest poor lapse rates and weak buoyancy. For these reasons have lowered severe probs across much of IL/MO due to limited instability. Otherwise, forced squall line could certainly produce isolated severe wind gusts but the more robust convection should remain across the Ozark Plateau and points south. ..Darrow/Leitman.. 04/26/2017Read more
from SPC Forecast Products http://ift.tt/s7Jkvo
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