SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0253 PM CDT Sun Apr 20 2025 Valid 202000Z - 211200Z ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS NORTHERN ARKANSAS AND MISSOURI VICINITY... ...SUMMARY... Severe thunderstorms are expected today across parts of the ArkLaTex into the Ozarks and mid Mississippi Valley, mainly this afternoon and evening. The best corridor for tornadoes (some of which could be strong) and scattered to numerous damaging winds should exist from central/northern Arkansas into Missouri. ...20z Update.. A broken line of thunderstorm activity continues near the surface low in northeastern OK/southeastern KS and along an attendant surface cold front extending from eastern OK southward into northeastern Texas/southern Arkansas. This activity is expected to continue to shift north and eastward through time as the low tracks to the east through the afternoon and evening. Storm intensity has been increasing over the last couple of hours, owing to daytime heating ahead of the front, where MLCAPE around 500-1500 J/kg is observed in surface objective analysis. VAD profiles across eastern Arkansas northward into Missouri show strong low-level shear in place, with large curved hodographs and rich low-level SRH. This trend will continue with the strengthening low-level jet lifting through the Mississippi Valley into the Midwest this evening, supporting risk for embedded supercells and tornadoes, a few of which may be strong. In addition to the tornado threat, bowing structures along the front will support risk for damaging winds. See MCD#502 and MCD#504 for more information. Thunderstorm coverage will increase along the southern portion of the front in central/eastern Texas into Louisiana through the afternoon and evening. This region is somewhat removed from the area of greater low and mid-level flow, which will keep severe potential more limited. See previous discussion for more information. ..Thornton/Goss.. 04/20/2025 .PREV DISCUSSION... /ISSUED 1129 AM CDT Sun Apr 20 2025/ ...Synopsis... A compact upper low currently moving into western Oklahoma will shift quickly northeastward this afternoon and tonight, crossing eastern Kansas and western Missouri this evening and then continuing northeastward across Iowa and into Wisconsin tonight. Fast southwesterly flow aloft will exist in advance of this system, within the tight height gradient between this feature and the persistent ridge centered over the Southeast. At the surface, a developing low analyzed over western Oklahoma at 15Z is forecast to progress northeastward across southeastern Kansas and Missouri through the afternoon, and then should continue northward toward -- and eventually into -- southern Wisconsin by early Monday morning. While a warm front lifts northward across the Mid Mississippi Valley/Midwest, a cold front trailing from the low will sweep eastward into/across Missouri and Arkansas this afternoon and evening, and then across the Mid and Lower Mississippi Valleys through the end of the period. ...Northeastern Texas northeastward to the western Illinois vicinity... An expansive area of multi-level cloud cover, along with ongoing convection, is evident across western and northern portions of the risk area late this morning, which continues to retard more substantial heating at this point. With that said, some breaks in the clouds are evident per recent visible imagery as far west as eastern Oklahoma, with thinning cloud cover with eastward/northeastward extent into Arkansas and the Ozarks. As the surface low over Oklahoma deepens through the day in tandem with the advance of the upper low, northward advance of the warm front with time will allow a moist boundary layer to likewise overspread much of Missouri and Illinois through sunset. This, combined with at least modest heating across portions of the area should yield an amply unstable environment (500 to near 1500 J/kg mixed-layer CAPE) to gradually evolve -- supporting a steady increase in convective coverage and intensity this afternoon. In contrast to the rather modest thermodynamic environment, a very favorable low-level and deep-layer wind field is evident, with respect to development of organized/rotating storms. An 80 kt mid-level jet will spread northeastward across the risk area with time, atop a 50-plus kt low-level jet. This will support vigorous updraft evolution, with all-hazards severe risk evolving as a result. At this time, it remains apparent that tornado potential -- including risk for a couple of strong tornadoes -- should maximize across the Ozarks, and areas just north and south, as surface winds back to southeasterly ahead of the deepening/advancing surface low. The primary risk should evolve with an anticipated, broken band of storms within the cold-frontal zone, including embedded supercells. Along with the tornado potential, fairly widespread coverage of damaging wind gusts is also expected, as complex, LEWP/bow-type structures are expected within the band of storms, as convection advances eastward across Missouri and Arkansas toward the Mississippi Valley through the afternoon and into the evening hours. Severe risk is expected to expand as far north as southeastern Iowa and adjacent western Illinois this evening, where weaker instability is expected, and as far south as eastern Texas where a weaker wind field with southward extent should limit severe potential on the southern fringe. Risk should very gradually diminish overnight as convection shifts eastward across the Mid-Mississippi Valley.