There has been an upgrade to tomorrow's severe threat from central Nebraska into Iowa, who are now in a level 3 risk. Storms tomorrow will initiate over the northern High Plains and rapidly expand in coverage into the SD/NE vicinity by the middle to late afternoon hours. While these initial cells will carry the potential for large hail and a brief concern, these aren't the reason for the upgrade. Rather, these storms are expected to grow upscale into one or more powerful storm complexes fueled by strong instability, deep moisture, and an increasing low-level jet. Due to the wind threat being more concentrated than it looked earlier, there was enough confidence to increase the severe threat in this region.
Also new is that the level 2 risks we had prior have now combined, with portions of the Midwest and Ohio Valley now within it. Intense daytime heating from our heat wave combined with a moist airmass will lead to an environment virtually uncapped. Westerly winds aloft will lead to longer-lived storm clusters that will pose primarily the threat of damaging winds.