6AM Day 1 Convective Outlook for Tuesday, February 17. NO SEVERE THUNDERSTORM AREAS FORECAST
SUMMARY
The risk for severe storms appears low, but isolated thunderstorms will be possible across parts of the West, and across the Upper Midwest late this afternoon and tonight.
Western States/Coastal California
A prominent upper-level trough will continue to settle south-southeastward along the West Coast through tonight, with a strong upper speed max nosing across central/southern California late today into tonight. North of the upper jet, very cold temperatures aloft will exist which will result in a few hundred J/kg SBCAPE, mainly for northern/central coastal areas today. While gusty winds and/or small hail could occur, organized severe storm potential is currently expected to remain low.
Upper Midwest
Consequential height falls will steadily occur regionally by late afternoon into tonight as a lead shortwave trough emerges from the northern/central High Plains. A related surface low will develop generally eastward across South Dakota/northern Nebraska toward Minnesota overnight. A moisture-limited warm sector, featuring mostly 40s with a few lower 50s F surface dewpoints, will shift north-northeastward toward the region in advance of an eastward-accelerating cold front.
Surface heating/boundary-layer mixing will steepen low-level lapse rates into afternoon in vicinity of the surface low/front, and while capping may tend to largely prevail during the day, a few thunderstorms could occur before sunset initially across the eastern Dakotas and/or far eastern Nebraska. Some convectively enhanced wind gusts are plausible given the steep lapse rates and strong deep-tropospheric wind field. Elevated thunderstorms will otherwise become more probable east-northeastward into evening and beyond across the Upper Midwest. Instability does not appear strong enough to support severe hail with this elevated activity.