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Severe Storm Outlook Narrative (AC)
Issued by NWS
Issued by NWS
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682 ACUS01 KWNS 281631 SWODY1 SPC AC 281630 Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1130 AM CDT Fri Jun 28 2024 Valid 281630Z - 291200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF THE CENTRAL PLAINS TO THE MID MISSISSIPPI VALLEY... ...SUMMARY... Large hail, damaging winds, and a couple of tornadoes may occur from parts of the central Plains into the mid/upper Mississippi Valley this afternoon and tonight. ...Synopsis... An upper low over the northern Rockies/High Plains will progress eastward today to the Upper Midwest. At the surface, an occluded low is forecast to meander slowly eastward over northern MN through this evening, while a secondary low consolidates over central KS. An occluded/cold front extending from the northern MN low will develop slowly southeastward across the central Plains and mid MO Valley this afternoon. This boundary will likely serve as a focus for strong/severe convection later today. ...Central Plains into the Mid Mississippi Valley... Better forcing for ascent associated with the upper trough/low should generally remain displaced to the north of the central Plains and mid MO Valley through much of the day. Also, the lingering effect of morning clouds/precipitation will be to slow diurnal destabilization to some extent. Still, low-level convergence along the cold front and glancing large-scale ascent will probably be sufficient for convective initiation through 20-00Z across parts of IA into eastern NE, and northeast KS into northern MO. Even modest daytime heating of the moist low-level airmass ahead of the front will support a narrow corridor of moderate to locally strong instability. Strengthening westerly winds through mid/upper levels will foster strong deep-layer shear and updraft organization. Initial development along the cold front from eastern NE into central IA may be supercellular, with an associated threat for large hail. Upscale growth into clusters and short line segments with a greater severe/damaging wind threat seems probable with time this evening. The eastern extent of the severe risk across the mid MS Valley will be modulated by the narrow zone of stronger instability, and convection should gradually weaken as it continues eastward late this evening and overnight. The tornado threat across these areas today appears less clear. While a modest southwesterly low-level jet will aid in sufficient low-level shear for updraft rotation, it remains unclear whether multiple supercells will be able to persist into the early evening hours. Still, some threat for a couple tornadoes remains apparent, mainly near/northeast of the surface low in northeast KS and vicinity where low-level shear should be locally maximized. A separate area of high-based convective development should occur this afternoon across the central High Plains, along/north of the cold front in a weak low-level upslope flow regime. This activity will move generally east-southeastward through the evening through a very well-mixed boundary layer, with generally weak to moderate instability present. Although low-level winds should remain modest, gradually increasing westerly flow at mid/upper levels should support sufficient deep-layer shear for convective organization. Severe/damaging winds appear to be the main threat as one or more small clusters continue east-southeastward across western/central NE/KS late this afternoon and evening. Isolated gusts of 75+ mph may occur if convection can become well organized into a small bowing cluster. Some large hail also appears possible, particularly with any initial supercells. ...Northern Plains into the Upper Mississippi Valley... Isolated to scattered thunderstorms should develop along an occluded front extending into parts of ND as the upper trough/low moves eastward over the northern Plains today. While instability appears fairly modest, occasional hail and strong/gusty winds may occur with the more robust convection given the presence of sufficient deep-layer shear. ..Gleason/Thornton.. 06/28/2024 $$