Subj : DAY1SVR: Day 1 Convective To : All From : Mike Powell Date : Wed Apr 19 2023 15:21:00 ACUS01 KWNS 192002 SWODY1 SPC AC 192000 Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0300 PM CDT Wed Apr 19 2023 Valid 192000Z - 201200Z ....THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS NORTHEAST KANSAS...SOUTHEAST NEBRASKA...NORTHWEST MISSOURI...AND SOUTHWEST IOWA... ....THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS CENTRAL OKLAHOMA INTO WESTERN NORTH TEXAS... ....SUMMARY... Multiple rounds of scattered severe thunderstorms are expected from late afternoon into tonight across the Mid-Missouri Valley. Very large hail is likely, and significant severe wind gusts along with a few tornadoes will be possible. A conditional threat for isolated significant severe storms also exists farther south into western/central Oklahoma and western north Texas this evening. ....Discussion... The only substantial changes this outlook update include the following: 1) shift the severe probabilities farther east where the dryline has moved east across parts of northern and western OK. 2) Reduced severe probabilities across northern OK/far south-central KS and bifurcated Slight-Risk equivalent severe probabilities into a northern and southern area. This change appears supported by both a strong consensus in model guidance showing the favored corridor for thunderstorms (severe) along the dryline to be over southwest and central OK later this afternoon/evening. Additionally, some of the model guidance simulating storms was aggressive with boundary-layer moisture compared to the 19 UTC Norman, OK raob (11.9 g/kg mean w). Specifically, the NSSL ARW high-resolution model was nearly 2 g/kg lowest 100 mb mean mixing ratio too moist. The 12 UTC FV3 model run depicted the boundary layer structure very well when compared to the observed raob. It remains plausible both based on the FV3 and observational trends that one or a couple of storms will develop along the dryline and potentially pose a severe hazard. Elsewhere, the forecast remains on track and no change was warranted. ...Smith.. 04/19/2023 ..PREV DISCUSSION... /ISSUED 1139 AM CDT Wed Apr 19 2023/ ....Mid-MO Valley... Three rounds of severe potential appear increasingly evident across the Mid-MO Valley vicinity beginning in the late afternoon and continuing tonight. The first should consist of elevated thunderstorms north of the slow-moving/quasi-stationary warm front that is arcing east of the initial primary surface cyclone over southeast NE. This activity near the NE/SD/IA border will probably evolve into a couple of elevated supercells within an eastward-moving cluster, owing to favorable cloud-bearing shear along the northern gradient of the peak buoyancy plume across the central Great Plains. Large hail will be the primary hazard. A separate area of dryline to warm-sector storm development is anticipated towards the KS/NE/MO/IA border during the early evening in the exit region of a strengthening low-level jet in OK/KS/MO. This ascent combined with the boundary-layer thermal ridge from western OK to central/eastern KS should be enough to overcome the pronounced elevated mixed-layer across the Great Plains. 12Z NAM guidance remains terribly inconsistent with the 00Z ECMWF, recent RAP guidance, and comparison to surface observations. It is already much too cool with current temperatures with it's typical too cool/moist boundary layer. It appears more likely that a relatively well-mixed boundary layer within this portion of the warm/moist sector will be characterized by surface dew points from 58-61 F as storms form. This will seemingly support a mix of large hail, damaging wind gusts, and a couple tornadoes with supercells that initially form. Given a relatively confined buoyancy plume, regenerative convection is likely through the evening, yielding a broadening cluster with embedded supercell structures. Tonight, a third round of severe storms should develop near the south-central NE/north-central KS border. This should occur as a lee cyclone over the central High Plains shifts east, in association with a shortwave impulse progressing through the basal portion of the broader mid-level trough over the West. A surge of low-level moisture northwestward amid an intense 60-70 kt low-level jet should support emerging elevated supercell clusters that track east overnight, potentially merging with lingering convection downstream. Severe wind gusts and large hail will be the primary threats. ....Western/central OK into western north TX... Storm development is uncertain along the dryline during the late afternoon to early evening, given little in the way of height falls/forcing for ascent, and the presence of a substantial warm-sector cap. Storm initiation will rely on the depth of mixing with surface heating along the dryline, and on parcel residence time in the dryline zone of ascent. Flow in the 850-700 mb layer will be a bit more parallel to the dryline compared to yesterday, which may allow long enough residence times to reach an LFC. If storms form, the environment favors a threat of isolated very large hail with any sustained supercell. During the evening, substantial intensification of the low-level jet and an increase in boundary-layer moisture renders concern for a conditional strong tornado threat after dusk. Overall moisture appears a bit less compared to past nocturnal intense tornado events and confidence is low in whether a supercell or two can become established prior to increasing MLCIN during the late evening. As such, confidence in occurrence/coverage is low, but intensity is conditionally significant. $$ --- SBBSecho 3.14-Linux * Origin: Ilink: CCO - capitolcityonline.net (454:1/105) .