Figure 9.  Several fields are overlaid and looped (12 to 16 UTC on 6 April 2003) to show the onset of widespread convective precipitation, and the first MCS. The background image indicates RUC model divergence at 250 mb (greatest div is shaded in green), and is overlaid by surface frontogenesis (cyan), surface observations, and the one hour lightning plot. Increasing upper divergence aided an expanding area of elevated convective precipitation north of the strengthening surface front. At the same time, supercell thunderstorms erupted south of the primary synoptic scale boundary and eventually congealed into the first MCS.