Subj : DAY1SVR: Day 1 Convective Outlook To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sun Jul 30 2023 12:56:07 ACUS01 KWNS 301256 SWODY1 SPC AC 301254 Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0754 AM CDT Sun Jul 30 2023 Valid 301300Z - 311200Z ....THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER PARTS OF THE CENTRAL/NORTHERN GREAT PLAINS... ....SUMMARY... Severe-thunderstorm potential should be best organized over parts of the central/northern Great Plains. ....Synopsis... In mid/upper levels, a series of convectively generated/enhanced perturbations in the subtropical easterlies have distorted the longstanding/intense Southwestern anticyclone, reshaping it into a configuration centered over the San Juan Mountains, and extending from there to southern CA and the northwestern Gulf of Mexico. A high-amplitude ridge -- initially positioned from the high through the central/northern Rockies -- will shift slightly eastward and weaken a small amount during the period. A series of low-amplitude shortwaves is evident in the associated flow, across NV/ID/MT. The eastern CONUS mean trough persists downstream, with two main embedded shortwave perturbations: 1. Over the coastal Carolinas and vicinity, forecast to eject northeastward and removed from areas near land by 00Z. 2. Over the Mid-South/Tennessee Valley region, with prior convective vorticity enhancement. This feature should shift slowly southeastward in strongly difluent, weakening mid/upper flow, toward the FL Panhandle and northern FL through the period. The 11Z surface analysis showed a cold front from oceanic waters offshore of the Mid-Atlantic, west-southwestward over KY and central MO, becoming a wavy, quasistationary to slow-moving warm front across eastern/northern NE, western SD, and east-Central MT, to another low near BZN. This boundary should move little through the day across the central/northern Plains, with a moist axis remaining mostly to its south from KS to SD, then northward over extreme eastern MT/western ND. ....Northern/central Great Plains... Isolated to scattered thunderstorms -- some as supercells, but most organizing fairly early into bands or clusters -- are expected to develop this afternoon and move eastward to southeastward over the outlook area. Activity also may form along the front, or a weak surface trough/confluence axis to its north over northeastern MT. This convection will initiate as one and perhaps two proximal shortwave perturbations crest the mean ridge and approach the area. Any supercells may offer large hail (some 2 inches or more in diameter) and a marginal tornado threat, while severe wind would be the greatest hazard from multicellular clusters/bands. The low-level air mass along and within about 100 nm either side of the moist axis should maintain 50s to low 60s F surface dewpoints into diurnal heating, beneath steep midlevel lapse rates. This will foster a corridor of relatively maximized MLCAPE up and down the central/northern High Plains, with values around 1000-1500 J/kg possible over parts of central/eastern MT and northeastern WY, increasing to 2000-3000 J/kg over western SD and west-central NE. Representing modest speeds veering strongly directionally with height, low-level hodographs are not expected to be particularly large, but favorable long, amidst effective-shear magnitudes ranging from near 60 kt in northern areas to 45-50 kt over NE. This will favor production of large to significant hail. Hail and strong-severe downdrafts should be well-maintained to the surface through strongly mixed subcloud layers with nearly dry-adiabatic lapse rates. ....Southeast... Widely scattered to scattered thunderstorms are forecast to develop near and south of the frontal zone to the Gulf Coast, mainly during the afternoon to early-evening hours when surface temperatures are warmest and already weak MLCINH is minimized. The convective environment will be aided somewhat by subtle large-scale ascent related to the slowly southeastward-moving, second shortwave trough described above. Rich low-level moisture abounds in the prospective development/inflow region of these storms, with surface dewpoints commonly in the upper 60s to mid 70s F, and high PW. Deep-layer winds will be modest, keeping vertical shear weak, and limiting storm organization to multicells regulated largely by mesobeta- and smaller-scale effects (such as localized clustering and cold-pool aggregation). Severe potential appears to be rather poorly focused and marginal overall, with damaging to isolated severe gusts as the main concern. ....AZ/Southeastern CA... Isolated to widely scattered thunderstorms are expected to develop again this afternoon over higher terrain of southern AZ. Activity should move approximately westward over adjoining desert floors through the remainder of the afternoon and into the evening, where deeply mixed subcloud layers will support strong-severe downdrafts. Storm organization and persistence may be more than previous days, owing to slightly deeper/stronger gradient flow aloft north of the Mexican height weakness, and to larger inflow-layer moisture content for greater buoyancy (MLCAPE potentially 500-1000 J/kg). ...Edwards/Broyles.. 07/30/2023 $$ = = = To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. 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