SPC 1730Z Day 2 Outlook
Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 1227 PM CDT Sat Oct 10 2020 Valid 111200Z - 121200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS PARTS OF THE NORTHERN/CENTRAL PLAINS INTO THE UPPER MIDWEST... ...SUMMARY... Isolated strong to severe thunderstorms may occur Sunday across parts of the northern/central Plains into the Upper Midwest, with marginally severe thunderstorms also possible across parts of the Southeast and Mid-Atlantic. ...Synopsis... ...Northern/Central Plains into the Upper Midwest... A strong shortwave trough is expected to move into the Plains on Sunday, contributing to the development of a mid-level cyclone across Saskatchewan by Sunday afternoon. This shortwave trough will also feature enhanced mid-level flow, which will spread across the Plains early Sunday and into the Upper Midwest by Sunday evening. The deepening mid-level cyclone will be accompanied by an occluding surface low and attendant cold front. Early Sunday, this cold front will likely extend from central Saskatchewan south-southeastward to another low in central ND and then southwestward back across central WY. A surface trough/dryline will also extend south from the ND surface low into the TX Panhandle. This surface features are expected to push eastward throughout the day, with the faster motion of the cold front allowing it to eventually overtake the dryline Sunday evening. Low 60s dewpoints will likely be in place ahead of the front from the central Plains into the Upper Midwest. A strong elevated mixed layer will likely cap convection throughout much of the afternoon. Even with this capping, ascent along the front, augmented by increasing large-scale forcing, should be able to overcome the convective inhibition as the front reaches far eastern Dakotas/middle MO Valley. This scenario favors quick linear development, with little opportunity ahead of the front for cellular convection. Even so, the presence of steep mid-level lapse rates suggest the possibility of severe hail in the strongest cores. Strong low to mid-level flow will also contribute to a damaging wind threat along the fast-moving cold front as it surges eastward. Limited instability casts doubt on how much the squall line can organize, with some undercutting of updrafts likely. However, this limited instability may be countered by the strong flow, and the general expectation is that strong, convectively augmented gusts are probable along the front for at least a few hours during the late afternoon and evening. Decreasing instability with eastern extent adds to uncertainty on the eastern extent of the damaging wind threat, but current thinking is that the line will outpace the instability ahead of it as it reaches central IA/MN. ...Southeast/Mid-Atlantic... Current NHC forecast of Tropical Depression Delta places it over central TN early Sunday morning, before the system then progresses northeastward throughout the day. Mid-level flow will gradually decrease as the overall system weakens. However, enough vertical shear will remain present over the warm, moist, and modestly unstable warm sector to support isolated strong to severe storms, particularly in areas where even modest heating can occur. Primary threat from any stronger storms is damaging wind gusts, but a tornado or two is also possible, especially near the warm front. ..Mosier.. 10/10/2020
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