SPC Mar 26, 2018 2000 UTC Day 1 Convective Outlook

By Newsroom America Feeds at 26 Mar 2018

SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0255 PM CDT Mon Mar 26 2018 Valid 262000Z - 271200Z ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS FROM PARTS OF SOUTH CENTRAL OKLAHOMA SOUTHWEST TO THE TRANSPECOS REGION OF TEXAS... ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS SURROUNDING THE ENH RISK AREA... ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS SURROUNDING THE SLGT RISK AREA... ...SUMMARY... Scattered large hail events, a few of which may be significant, are likely from the Texas Big Country into southwest Oklahoma between now and 12 am CDT. Isolated to scattered severe wind gusts and a brief tornado or two are also possible. ...Discussion... Aside from some minor line adjustments -- particularly over the Texas South Plains area where dry air has spread into portions of the SLGT and ENH risk areas behind the surface boundary -- the ongoing forecast/reasoning remains valid. For additional short-term forecast information, please refer to SWOMCD #176. ..Goss.. 03/26/2018 .PREV DISCUSSION... /ISSUED 1130 AM CDT Mon Mar 26 2018/ ...Southern Great Plains... Have amplified the probabilities resulting in a hail-driven upgrade to Enhanced risk given the likelihood of numerous storms along the dryline this afternoon and evening. Large hail should be the predominant hazard (some of which could be significant) given wind profiles favoring initially semi-discrete supercells evolving into multiple clusters, with unremarkable low-level winds limiting the tornado hazard. A surface cyclone over south-central KS will weaken as it tracks into northern MO this evening, with the dryline mixing across western OK and remaining nearly stationary across the eastern Permian Basin. With pervasive low to mid 60s surface dew points ahead of the dryline and ample diabatic heating across TX, a plume of MLCAPE from 1500-2500 J/kg should develop by mid-afternoon amid steep 700-500 mb lapse rates around 7-8 C/km. While low-level wind profiles will be weak and exhibit veer-back-veer tendency with height, deep-layer speed shear will be strong with effective values from 50-60 kt. Guidance is rather consistent in suggesting extensive storm development along the dryline by late afternoon and evening. This setup should favor several initially semi-discrete supercells transitioning into multiple clusters and ultimately a nearly continuous band of convection towards late evening. Large hail should be the primary hazard, especially during the late afternoon to early evening, before evolving into more of a mixed wind/hail mode during the evening. The tornado hazard will be tempered by wretched J-shaped low-level hodographs. A warm-sector cap and mixing of relatively shallow low-level moisture across central TX this afternoon (per the shallow moist layer in the 12Z Brownsville and Corpus Christi soundings) both suggest that the severe threat will be confined to a narrow zone along/just ahead of the dryline. More widespread convection with time will reduce mid-level lapse rates, such that the severe threat will diminish overnight. Read more



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