Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 1225 PM CDT Tue Jul 18 2017 Valid 191200Z - 201200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM THE NORTHERN PLAINS ACROSS THE UPPER MISSISSIPPI VALLEY... ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS SURROUNDING THE SLIGHT RISK FROM THE NORTHERN PLAINS AND UPPER MIDWEST... ...SUMMARY... Severe storms will be possible over portions of the north-central U.S. Wednesday and Wednesday night, most likely from eastern South Dakota, southern Minnesota, northern Iowa into western Wisconsin. ...Synopsis... Model guidance is consistent indicating a low amplitude mid-level short wave perturbation will move through the upper ridge over the northern High Plains tomorrow and turn east-southeastward across the upper Midwest. This will be associated with a band of stronger mid/upper level winds forecast to move across the northern Plains and upper Mississippi Valley. At the surface, the frontal boundary currently extending across the upper Midwest is likely to provide a primary focus for strong-to-severe thunderstorm development especially tomorrow afternoon and night. ...Northern Plains into the Upper Mississippi Valley... Scattered mainly elevated convection may be occurring early in the period over parts of North Dakota and possibly northern South Dakota. The environment south of the aforementioned boundary is forecast to become increasing warm/unstable as diabatic heating occurs beneath an EML plume extending across parts of South Dakota into southern Minnesota. The cap associated with the EML is likely to inhibit surface-based storm initiation, particularly south of the surface front, into the afternoon hours. The air mass is expected to become quite unstable along/south of the front from parts of eastern South Dakota across southern Minnesota and northern Iowa with MLCAPE of 1500-3000 J/kg. Forecast soundings exhibit veering wind profiles with height as a southwest LLJ develops by later afternoon and evening, with deep layer shear of 40-50 kt over the region. The severe storm threat is expected to increase during the afternoon as morning storms in the Dakotas progress eastward and new storms develop along and north of the boundary. The environment will be favorable for some initial storms to develop supercell characteristics, with model guidance suggesting eventual upscale growth with potential for QLCS bowing segments to spread east-southeastward by late afternoon and evening. All severe hazards will be possible with the initial severe storms, with potential for an increased damaging wind threat developing during the second half of the period in association with forward-propagating bowing line segments. Despite uncertainty in the details of convective storm development and evolution, sufficient confidence in severe potential exists to introduce a 15% total severe/SLGT Risk in this outlook. However, the area will need to be monitored closely for a potential upgrade in subsequent Day 1 Outlooks. ..Weiss.. 07/18/2017Read more
from SPC Forecast Products http://ift.tt/ws9HZn
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