Severe Storm Outlook Narrative (AC)
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Issued by NWS
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686 ACUS01 KWNS 111958 SWODY1 SPC AC 111957 Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0257 PM CDT Thu Jul 11 2024 Valid 112000Z - 121200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER PARTS OF SOUTHERN ARIZONA... ...SUMMARY... Severe thunderstorm wind gusts are possible over parts of southern Arizona from mid-afternoon through early/mid-evening. Little change was necessary for the 20Z update. The primary of severe risk continues to be over parts of southern AZ, downstream of storms now developing along the Rim. The air mass is destabilizing with heating with 500-1000 J/kg MUCAPE currently. Modest northeast winds in the midlevels and the unstable surface air mass should foster west/southwestward propagation later today, with strong to locally severe gusts possible. For more information see mesoscale discussion 1579. ..Jewell.. 07/11/2024 .PREV DISCUSSION... /ISSUED 1145 AM CDT Thu Jul 11 2024/ ...Arizona... Widely scattered to scattered thunderstorms are expected to develop this afternoon over the Mogollon Rim, and smaller mountain ranges to the south. That will occur as strong insolation at those higher elevations preferentially removes MLCINH, in the presence of generally greater low-level moisture than previous days. Some strengthening of flow aloft is expected over this region on the southeast periphery of the upper anticyclone. This will support convective motion off the Rim (and small mountain ranges to its south), into strongly heated/deeply mixed boundary layers of the desert floor. Isolated strong-severe gusts are possible from the relatively early, more-discrete activity, and swaths of strong-severe gusts are possible as convection moves southwestward toward the international border. ...Northern High Plains... Isolated to widely scattered, high-based thunderstorms are expected to form near the lee trough, where both relatively maximized convergence and strong surface heating should contribute to enough lift for convective initiation. The main concern should be damaging to severe gusts, given the deeply mixed subcloud layer. Isolated severe hail also may occur, amidst enough deep-layer shear for some organized thunderstorms (effective-shear magnitudes of 30-40 kt). Lack of greater moisture and buoyancy will be a limiting factor for coverage and intensity of convection, which should diminish rapidly after sunset. ...Southeast Kansas/Southern Missouri... A few severe storms could develop today to the east-northeast of a surface wave near the Oklahoma/Kansas border in vicinity of front that extends into Missouri, which may be somewhat effectively augmented by lingering early day convection. Moderate to locally strong buoyancy will exist within a moist environment, with MLCAPE likely to reach 2500-3000 J/kg. A considerable vertical veering of winds will exist through the lower/middle troposphere, with around 30 kt effective shear. Instances of severe hail and/or wind gusts could occur. ...Southern Maine... Clouds have lingered much of the morning with rather weak lapse rates noted in the 12z KGYX/Gray Maine observed sounding, but clearing is occurring from the west and a narrow zone of modest destabilization should occur this afternoon, within a very moist environment (lower/middle 70s F surface dewpoints) ahead of a cold front. Pending sufficient destabilization, a locally severe storm or two could occur, potentially with an absence of lightning, in the presence of long/semi-straight hodographs (highlighted by 45-50 kt winds 3-6 km AGL). ...Central/south-central portions of Illinois and Indiana... Ample low-level CAPE (100+ J/kg 0-km AGL) near the southward-shifting boundary could lead to some potential for funnels or perhaps even a brief non-supercell tornado this afternoon. Some of the storms could otherwise pose a risk for gusty winds, but the overall potential for organized severe storms is currently expected to remain low. $$