Subj : DAY1 Enhanced Risk Plains To : All From : Dumas Walker Date : Tue Jul 02 2024 08:33 am ACUS01 KWNS 021253 SWODY1 SPC AC 021251 Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0751 AM CDT Tue Jul 02 2024 Valid 021300Z - 031200Z ....THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS OVER PARTS OF SOUTHERN IOWA...NORTHERN MISSOURI...NORTHEASTERN KANSAS...AND EXTREME SOUTHEASTERN NEBRASKA... ....SUMMARY... Damaging thunderstorm winds, a few tornadoes, and large hail are most likely this afternoon and early evening over southern Iowa, northern Missouri, and northeastern Kansas. ....Synopsis... Broadly cyclonic flow in mid/upper levels will persist from the Pacific Northwest across the central/northern Rockies to the Upper Great Lakes. Within that, a series of shortwave troughs were apparent, the most prominent over the CONUS being located initially across WY and northeastern UT. This perturbation should move eastward to eastern SD and central NE by 00Z, cross the upper Mississippi Valley overnight, and reach parts of WI and the Upper Peninsula of MI by the end of the period. As that occurs, a persistent subtropical high over the Arklatex region will shift eastward over the Delta region, but with attached ridging expanding back across central and west TX to near ELP. Another attached ridge will shift eastward across the Ohio Valley and Lower Great Lakes. At the surface, 11Z analysis showed a surface low near HLC, with cold front southwestward across extreme southeastern CO and northeastern/north-central NM. A warm front arched from the low across southeastern NE, then southward near the KS/MO and AR/OK borders. The warm front should move northeastward to the mid Mississippi Valley today while the low moves northeastward and weakens. Meanwhile, by 00Z, the cold front should reach western IA, northeastern through south-central KS, and the northern TX Panhandle. becoming a warm front into a deepening low over southeastern CO. By 12Z, the cold front should reach northern IL, central/southwestern MO, north-central OK, then into the low, which will have sagged into the northern TX Panhandle. ....IA/MO/northeastern KS and vicinity... A swath of decaying convection and associated cloud shield are ongoing from Lower MI to IA and parts of southeastern NE and northwestern MO. This plume of clouds/precip should continue to shift east-northeastward and erode through the day, but leave behind an outflow/differential-heating boundary that, southwest of the synoptic warm front, should act as the primary convective influence ahead of the cold front. Convergence near these boundaries, and strong heating in the richly moist warm sector between, will support scattered afternoon thunderstorms. This will include the potential for a few supercells with tornado and large-hail threats, whether relatively discrete early in the convective cycle, or embedded in subsequent quasi-linear evolution. That upscale convective organization also will maximize severe-wind potential from late afternoon into early evening, before activity encounters a more-stable, nocturnally cooling airmass farther east near the warm-frontal thermal gradient. In the preconvective warm sector, 70s F surface dewpoints should be common, as a Gulf-origin airmass blends with areas of evapotranspirative moisture contribution. Though mid/upper-level lapse rates will be modest, strong low-level destabilization will combine with a deep troposphere to contribute to MLCAPE in the 2000-3000 J/kg range. Effective-shear magnitudes will have a large range -- roughly 35-55 kt based strongly on boundary effects upon near-surface winds. Boundary-layer shear/hodographs will be greatest near the warm front and along any mesoscale boundaries between the fronts, locally maximizing supercell organization in low levels. ....Central/southern High Plains... Widely scattered to scattered thunderstorms are forecast to develop this afternoon over western portions of this area -- initially over relatively high elevations of southeast WY, east-central/ southeastern CO and northeastern NM, where diurnal heating will preferentially erode MLCINH. This activity should move generally eastward onto the adjoining High Plains, offering sporadic severe gusts and hail. The greatest concentration of convection (and associated severe potential) still appears most probable over southeastern CO, growing upscale as a complex and moving into parts of southwestern KS this evening. Vertical shear will be most favorable for supercells north of the front, where a substantial easterly component of boundary-layer flow will contribute to enhanced low-level shear, greater storm-relative low-level winds, upslope lift, and moist advection (to offset mixing-related moisture loss somewhat). The northern lobe of the (marginal) outlook area will be under the greatest mid/upper-level flow and strongest deep shear, but also will have weaker low-level moisture/theta-e and less buoyancy than farther south, with similar mid/upper-level lapse rates under a monsoonal plume as closer to the subtropical ridge. In the Arkansas River Valley region, activity moving into 50s to low 60s F surface dewpoints, with a strongly heated boundary layer, will encounter peak diurnal MLCAPE of 500-1500 J/kg across southeastern CO, and 1000-2000 J/kg into southwestern KS, amidst 45-55 kt effective-shear magnitudes, and long/nearly straight low-level hodographs favoring large hail with any discrete supercells. However, a well-mixed subcloud layer should support severe outflow and aggregation of outflows, leading to upscale clustering for a few hours before activity encounters too much CINH to remain severe over southern/central KS. Farther south, along and south of the front, deep-layer flow and shear will be weaker, as will buoyancy (due to drier, deeper mixed layers), but convection still may pose a threat for isolated severe downbursts. ...Edwards/Kerr.. 07/02/2024 $$ --- SBBSecho 3.20-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (21:1/175) .