This loop of Valley, Nebraska (unmodified) soundings throughout the day shows the change in vertical wind, temperature (red) and dew point (blue) structure at the nearest raob site to the low-level upstream of the Spencer storm. The 12Z moisture spike near 400 mb is spurious. Note that these soundings were launched 155 nautical miles from Spencer and probably do not represent evolution of the pre-storm and near-storm environment; but they still provide important clues about the large-scale changes in the area.

Some of the most notable features... The low level cap increases during the day -- while the cirrostratus veil (see long IR satellite loop) limits surface heating somewhat -- then nearly mixes out by 00z. [Obviously, the cap was weaker where the Spencer storm developed; this is represented in the modified 00Z sounding.] There is sharp increase in upper level flow with time, especially the 150-300 mb layer including the equilibrium/anvil levels, as the jet max moves nearly overhead (see 250 mb upper air map).