Deep systems like this are almost always accompanied by strong warm air advection, which can often destabilize the warm sector in a hurry, even through cloud cover. Dixie in particular often undergoes extremely fast airmass recovery due to its proximity with the gulf. 4/27 had a morning MCS, as an example, that actually produced several sigtors itself. There are a number of events that have been like this especially in dixie.
In fact, a morning MCS' is often a precursor to higher end events, as they often leave outflow boundaries that serve as focuses for both enhanced low level convergence (for initiation) and locally enhanced SRH.