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Severe Storm Outlook Narrative (AC)
Issued by NWS
Issued by NWS
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208 ACUS01 KWNS 240600 SWODY1 SPC AC 240558 Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1258 AM CDT Mon Jun 24 2024 Valid 241200Z - 251200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM THE UPPER MIDWEST TO THE CENTRAL PLAINS.... ...SUMMARY... Scattered severe thunderstorms will be possible over parts of the Upper Midwest, this afternoon and continuing overnight. A cluster of severe storms potentially capable of producing destructive wind gusts may develop over parts of Minnesota into Wisconsin though there remains significant uncertainty. ...Upper Midwest to the central Plains... A broad upper low with several embedded vort maxima and moderate west/southwestern flow over the Canadian prairies is forecast to move eastward and consolidate across portions of the Upper Midwest this afternoon and evening. Weak ascent will overspread a developing surface low and warm front lifting into the eastern Dakotas and western MN. Rich boundary-layer moisture (low 70s F surface dewpoints) is forecast to surge northward from the central Plains into the lower Red River Valley. Very warm temperatures (at the surface and aloft), steep mid-level lapse rates, and the returning moisture will prime an extremely unstable, but strongly capped troposphere, potentially supportive of all hazards. Multiple convective scenarios appear possible from late this afternoon through the overnight. Isolated surface-based thunderstorms may develop along the occluded front in eastern ND or near the triple point/warm front across northeast SD and western MN. While uncertain given the large inhibition, any storms that do form will likely organize into supercells given strong veering wind profiles and the very large buoyancy (MLCAPE >4000 J/kg). Large to very large hail, damaging winds and perhaps a tornado would be possible with any supercells, especially near the warm front with backed surface winds. Some CAM guidance suggests a cluster of storms could then track southeast along the warm front, potentially growing upscale into an MCS, with a damaging wind and hail risk into the overnight hours across the western Great Lakes. A second, potentially more significant, scenario may evolve if convection remains suppressed through the afternoon and instead develops along the southeastward surging cold front over the eastern Dakotas and western MN, or elevated storms intensify north of the warm front. With the 4000-5000 J/kg of MUCAPE present, rapid upscale growth into a damaging MCS/bow echo could result in the risk for widespread severe winds. This scenario remains highly uncertain given the warm temperatures aloft and unpredictable mesoscale storm interactions, but is reflected in several hi-res model solutions and by general pattern recognition. Should this occur, a swath of significant damaging winds may evolve along or just north of the buoyancy gradient across southern MN, southern/central WI and into portions of northern IL by 12z Tues. Considered an upgrade to level-3 Enhanced but uncertainty in storm development and evolution remains too high. ...Central Plains and Black Hills... Very warm surface temperatures are expected ahead of the weakening cold front across central NE and northern KS. Deeply mixed profiles may overcome very warm H7 temperatures to support widely scattered high-based storms. With generally weak mid-level flow across the region, storms may quickly become outflow dominant, but steep tropospheric lapse rates will support isolated severe gusts. The strongest updrafts may also be capable of producing some hail. High-based storms are also possible over the Black Hills where weak upslope flow is occurring behind the front. Limited moisture and only glancing upper-level support suggest storm coverage will remain isolated. Still, the deeply mixed air mass could support damaging gusts with any sustained storms. ...Carolinas... At the base of departing east coast trough, subtle height falls atop a warm and unstable air mass will support scattered afternoon thunderstorms across much of the eastern Carolinas along a weak surface cold front. Enhanced flow aloft and surface convergence near the front should be sufficient for transient storm organization into multi-cell clusters or a weak supercell. Steepening low-level lapse rates and the high PWAT air mass will favor heavily water and hail-loaded downdrafts capable of isolated damaging gusts. Storms should begin to move offshore by early evening ending the severe risk. ..Lyons/Wendt.. 06/24/2024 $$