####018004454#### ACUS01 KWNS 300559 SWODY1 SPC AC 300557 Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1257 AM CDT Tue Apr 30 2024 Valid 301200Z - 011200Z ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF THE MID MISSOURI VALLEY INTO THE CENTRAL PLAINS... ...SUMMARY... Severe thunderstorms will be possible this afternoon and evening from parts of the upper Mississippi Valley southwestward into the mid Missouri Valley, and central to southern Plains. The greatest threat is expected from western and central Iowa southwestward across far southeast Nebraska, far northwest Missouri into northeast Kansas, where very large hail, severe wind gusts (possibly above 70 mph) and a few tornadoes are expected. ...Upper Midwest/Mid Missouri Valley/Central Plains... An upper-level trough will move into the central and northern Plains today, as an associated 60 to 70 knot mid-level jet moves through the trough. At the surface, a deepening low will move into southeastern South Dakota, resulting in strong moisture advection across the mid Missouri Valley and central Plains. A north-northeast to south-southwest corridor of maximized low-level moisture will setup from eastern Kansas into western Iowa, where surface dewpoints will be in the lower to mid 60s F. Surface heating along this corridor will result in moderate instability by afternoon, with MLCAPE peaking in the 2000 to 3000 J/kg range. Ahead of the upper trough, large-scale ascent will likely support scattered thunderstorm development during the mid afternoon from eastern South Dakota into eastern Nebraska. This convection is expected to increase in intensity and coverage, moving eastward across Iowa, and developing south-southwestward into northeast Kansas during the late afternoon. A broken line of strong to severe storms will move east-southeastward toward the Mississippi River Valley in the early to mid evening. Along and near the instability axis, RAP forecast soundings at 21Z from near Omaha to Kansas City have supercell wind profiles, with strong speed shear in the low to midlevels and 0-6 km shear generally from 40 to 55 knots. Lapse rates are forecast to be very steep in the low to midlevels. 700-500 mb lapse rates around 8 C/km will be very favorable for supercells with large hail. The more dominant supercells should be capable of hailstones greater than 2 inches in diameter. 0-3 km lapse rates are forecast to be exceptionally steep, with some forecast soundings having 0-3 km lapse rates near 9 C/km. This should support a wind damage threat with supercells and the more intense short line segments. Wind gusts above 70 mph will be possible. Low-level shear should also be strong enough to support tornado development with the more intense supercells. The severe threat is expected to continue from late afternoon into the early to mid evening. The severe threat should become marginal by late evening, as the convective system moves through the lower Missouri Valley and southern sections of the central Plains. ...Southern Plains... West-southwesterly mid-level flow will be in place across the southern Plains today. At the surface, a corridor of maximized low-level moisture will be in place to the east of a dryline from western Oklahoma into west Texas. Surface dewpoints in the 60s F will contribute to the development of moderate instability by afternoon. MLCAPE is forecast to peak in the 2500 to 3500 J/kg range. Although large-scale ascent will likely be limited, low-level convergence near the dryline should result in isolated convective initiation during the mid to late afternoon. With any cell that can initiate and move away from the dryline, an isolated severe threat will be possible. RAP forecast soundings to the east of the dryline at 00Z/Wednesday generally have 0-6 km shear in the 30 to 40 knot range, with very steep lapse rates in the low to mid-levels. Some forecast soundings in western Oklahoma and northwest Texas have 0-3 km lapse rates near 9 C/km. This environment will likely be sufficient for organized cells with isolated large hail and strong gusts. The severe threat will be marginal from southwest Oklahoma into west Texas, where convective coverage is expected to be very isolated. ..Broyles/Thornton.. 04/30/2024 $$