For what it's worth, I departed Warracknabeal for Mildura at around 1610 yesterday. Began VFR but after take-off it soon became apparent that I wouldnt be able to maintain VMC at planned 4500 so chaged to IFR and entered IMC at around 3500, it became clear around 30NM north of YWKB and when I looked back to see how far it extended it was basically a wall of cloud / poor vis from the ground up and as far to the west as I could see, there was also a few returns on the storm scope. Wind from the ground up was a consistent 20Kt+ northerly and yes there were showers moving through.
I suppose this is the weather that would have still been prevailing around the time of the incident.
Have to agree with havick too.