Subj : DAY1SVR: Day 1 Convective To : All From : Mike Powell Date : Sat Apr 15 2023 17:49:00 ACUS01 KWNS 151953 SWODY1 SPC AC 151952 Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0252 PM CDT Sat Apr 15 2023 Valid 152000Z - 161200Z ....THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF CENTRAL AND SOUTHERN MISSOURI AND ADJACENT SOUTHWESTERN ILLINOIS...SOUTHWARD TO NORTHERN LOUISIANA... ....SUMMARY... Severe risk will continue this afternoon and tonight -- with greatest potential focused across the Mid-Mississippi/Lower Missouri Valleys. Within the main risk area, very large hail and damaging winds will be the dominant hazards in terms of coverage, but a few tornadoes will be possible. ....Discussion... The ongoing convective/severe-weather event continues to unfold largely as described in prior outlooks, with the most substantial severe risk evolving at this time across far eastern Oklahoma and into southern Missouri and northwestern Arkansas. Here, supercell development is underway, with very large hail being reported. This event will continue to expand in coverage, as the all-hazard risk evolves across this region. Less widespread risk is forecast to expand southwestward over the next several hours, while local/limited risk -- primarily in the form of strong winds -- continues for a couple more hours over the central Gulf Coastal area. Aside from minor line adjustments to account for recent convective evolution, no substantial changes to outlook areas appear necessary with this update. ...Goss.. 04/15/2023 ..PREV DISCUSSION... /ISSUED 1130 AM CDT Sat Apr 15 2023/ ....Mid MS Valley to the Gulf coast... A shortwave trough over the central Great Plains will shift east into the Mid-MS Valley through tonight. This trough has two embedded impulses, one across central KS and the other in eastern CO. The latter is expected to become dominant as the trough and attendant mid-level jet amplify, centered on this evening. The leading impulse will likely aid in initial surface-based thunderstorm development in the Ozark Plateau, immediately ahead of the primary surface cyclone along the northern return of richer boundary-layer moisture from eastern OK/western AR. Activity will expand northeast in MO, as well as develop south along and ahead of an eastward-moving cold front through AR to southeast TX. Weak low-level shear and rather modest hodograph curvature suggests that large hail will be the primary initial threat. Significant severe hail will be possible owing to very steep mid-level lapse rates initially and ample buoyancy amid 30-40 kt effective bulk shear. How quickly storms grow upscale from discrete supercells into a QLCS is somewhat uncertain, but is most likely to occur first across MO/northern AR towards the Mid-MS Valley in the late afternoon to early evening. This will yield a corresponding increase in the damaging wind threat. The 12Z NAM is substantially stronger than the 15Z RAP and 00Z ECMWF with the degree of low-level mass response ahead of the line in the early evening, lowering confidence in the degree of embedded tornado threat. The northern line of storms will weaken into tonight as storms spread east of the Mid-MS Valley amid diminishing buoyancy with eastern extent. Farther south, a messier mix of semi-discrete supercells and clusters might evolve into a southeast-moving QLCS spreading across the Lower MS Valley tonight. Low confidence exists in this scenario given potential for multiple rounds of convection this afternoon and evening. An ongoing MCS across LA/far southern MS may continue east along the central Gulf Coast with a primary threat of strong to isolated severe gusts. The track of this MCS this morning has yielded a swath of convective overturning in its wake, suggesting that weak low-level warm theta-e advection along/atop its residual outflow could support redevelopment of scattered storms around peak heating. Deep-layer vertical shear will be weaker with southern extent, but steep lapse rates and large undisturbed warm-sector CAPE will support potential for large hail/damaging winds late this afternoon/evening. $$ --- SBBSecho 3.14-Linux * Origin: Ilink: CCO - capitolcityonline.net (454:1/105) .