SPC AC 100549 Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1149 PM CST Thu Jan 09 2020 Valid 101200Z - 111200Z ...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS FROM SOUTHEAST OKLAHOMA INTO THE ARKLATEX... ...SUMMARY... Severe thunderstorms are expected across the southern Plains into the lower Mississippi Valley. Damaging winds are the greatest severe risk, though tornadoes are possible along with very large hail across the southern Plains. ...Southern Plains/Lower Mississippi Valley... Late-evening water-vapor imagery depicts a well-defined short-wave trough over AZ/northern Mexico, shifting east in line with latest model guidance. This feature is forecast to advance into the southern Rockies by 18z as 90+kt 500mb speed max rotates into the base of the trough south of the Big Bend region. In response to this trough, LLJ is forecast to increase across northwest TX which will enhance low-level warm advection across western OK. Low-level moisture is advancing northwest across OK and should aid buoyancy for elevated convection between 12-14z. Forecast soundings suggest elevated supercells are possible early in the period and this is supported by CAMs with a cluster of convection that will spread northeast across northern OK/southern KS. As this activity spreads east into upper 50s/lower 60s dew points, convection will have an opportunity to become surface based, though discrete cells may not be particularly common as a polar front sags into this region. Farther south, strong boundary-layer heating is expected across west TX where surface-3km lapse rates are forecast to approach 9 C/km. At the same time, strong mid-level height falls will spread across the southern Plains by peak heating, and thunderstorms should easily develop along the eastern edge of this steeper lapse-rate plume. Latest thinking is scattered supercells will evolve from east-central OK - north-central TX - southwestern TX between 19-21z. This activity will be strongly sheared and could produce very large hail early in the convective cycle. With time, multi-scale forcing will encourage an extensive squall line that should race east toward the Arklatex region. Damaging winds will likely be common along this squall line as it advances across eastern OK/east TX during the evening hours. Linear MCS will continue east during the overnight hours, advancing to near the MS River toward the end of the period. While damaging winds should be the primary threat with the squall line, very strong shear and moist profiles will likely result in embedded supercells. A few tornadoes are expected along the QLCS but the lack of confidence in discrete pre-frontal supercells will preclude more than 10% tornado probs during the day1 period. ..Darrow/Nauslar.. 01/10/2020 CLICK TO GET WUUS01 PTSDY1 PRODUCT NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 1300Z