SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0800 AM CDT Sun Oct 11 2020 Valid 111300Z - 121200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS THE UPPER MIDWEST AND MIDDLE MISSOURI VALLEY... ...SUMMARY... Severe thunderstorms are possible late this afternoon and evening across the Upper Midwest and Middle Missouri Valley. Some tornado and/or damaging wind potential will also exist across parts of the Carolinas. ...Upper Midwest/Middle Missouri Valley... Considerable upper-level trough amplification will occur over the northern High Plains/Dakotas today, with height falls reaching the Upper Mississippi River Valley and Middle Missouri Valley by late tonight. As amplification occurs, a considerable strengthening and backing of mid/high-level winds (50-80 kt at 500 mb; generally south-southwesterly) are expected across the region by tonight. The stronger winds aloft will be maximized just behind an east/southeastward-moving cold front. While moisture is quite limited early today, a steady moistening is expected with a northward-transitioning warm front. By late afternoon/early evening, a semi-narrow zone of upper 50s/lower 60s F surface dewpoints are expected near/just ahead of the east/southeast-advancing cold front. Mid-level capping will be prevalent much of the afternoon, particularly given the modest moisture scenario. Regardless, the increasingly pronounced forcing for ascent will be instrumental in the development/maturation of convection by late afternoon, and more so, into this evening. Such initial development is likely to occur generally near the border of the eastern Dakotas/western Minnesota into northwest Iowa, with other storm development occurring a bit later southwestward into eastern Nebraska/northeast Kansas. Forecast soundings suggest ample deep-layer shear for potential supercells capable of severe hail with initial development. However, the strong degree of forcing and influence of the cold front should result in relatively quick storm mergers, with the expected evolution of a semi-continuous squall line by mid-evening across southern Minnesota/western Iowa into southeast Nebraska/northeast Kansas. Accordingly, damaging winds will likely be an increasing concern this evening, while some line-embedded tornado risk cannot be ruled out. Overall storm vigor will likely diminish overnight as the storms encounter an increasingly stable boundary layer with eastward extent. ...Carolinas... The remnants of Delta will continue northeastward toward the southern Appalachians today. Early morning water vapor imagery shows substantial mid-level drying from Georgia into South Carolina/western North Carolina. The overall system will tend to weaken, as will low/mid-level winds preceding it. That said, some severe risk in the form of a brief tornado or two and/or locally damaging winds is still expected given sufficiently favorable low-level/deep-layer shear and a moist environment. While a particularly organized/sustained severe risk is not currently expected, a corridor near the South Carolina/North Carolina border in vicinity of the warm front would conditionally be the most favorable area for a tornado risk. ..Guyer/Goss.. 10/11/2020
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