Well we certainly need to find out the date of it to put any analysis on it.
Radar is available for the area - I'm guessing a little west of Jabiru or near Cooinda (as per radar locations)?
11th Feb has some late afternoon thunderstorms (7pm ish):
http://www.theweatherchaser.com/radar-loop/IDR632-darwin-berrimah/2011-02-11-00/2011-02-11-12
14th Feb has something in the Cooinda area around 4pm
http://www.theweatherchaser.com/radar-loop/IDR632-darwin-berrimah/2011-02-14-00/2011-02-14-12