Severe Storm Outlook Narrative (AC)
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Issued by NWS
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540 ACUS01 KWNS 180545 SWODY1 SPC AC 180544 Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1244 AM CDT Tue Jun 18 2024 Valid 181200Z - 191200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM THE UPPER MISSISSIPPI VALLEY TO THE CENTRAL HIGH PLAINS... ...SUMMARY... Scattered strong to severe storms will be possible this afternoon over parts of the Upper Mississippi Valley southwestward into the central High Plains. ...Upper Mississippi Valley to the central High Plains... A pronounced upper trough is currently evident over the northern Rockies. This feature is forecast to eject into the northern High Plains by 19/00z, then across MB/upper Red River region by the end of the period. While weak mid-level height falls will extend along this corridor early, much of the CONUS will actually experience neutral-weak height rises as the eastern US anticyclone dominates and builds west into the OH Valley. This evolution will result in a notable surface low tracking from eastern SD, across northern MN into western ON by mid afternoon. Building surface pressures over the Plains will force a cold front southeast and this boundary will serve as the focus for potentially strong/severe convection later in the day. Early in the period, strong low-level warm advection will prove instrumental in a zone of robust convection across the upper Red River Valley into western ON. As the LLJ lifts northeast in response to the short wave, the majority of elevated convection will progress north of the international border. Of more significance will be convection that develops later in the afternoon along/ahead of the cold front. Latest model guidance suggests modest boundary-layer heating will occur ahead of the wind shift and this should aid buoyancy for potential robust updrafts. Strongest mid-level flow and deep-layer shear will be noted across the upper MS Valley, but adequate shear will extend the length of the front into the central High Plains where a few supercells are expected to develop. The primary risk for organized updrafts will be during the late afternoon/evening hours when instability will be maximized. Large hail and damaging winds are the primary risks. ...Upper Ohio Valley into upstate NY... Water-vapor imagery depicts at least one significant disturbance rotating northeast around the anticyclone. This feature is currently located over IL and should contribute to diurnally-enhanced convection later today. Current trends/model guidance suggest this disturbance will advect into lower MI by 18z, then into southern ON by early evening. Surface heating should contribute to destabilization across the upper OH Valley into upstate NY and isolated-scattered thunderstorms will once again develop. Gusty winds are the primary concern with this weak-modestly sheared activity. ..Darrow/Thornton.. 06/18/2024 $$