cool, good luck this coming weekend, just remember i came up empty 4 days ago cause i underestimated how much rain was required. If i were you i would keep a close eye on the BoM Weather site, in particular:
http://www.bom.gov.au/weather/wa/observations.shtml
(its interesting how much rainfall can vary between Bridgetown and Donnybrook!)
I'd want to see Bal. recieve 20mm rain minimum within 3-5 days before i considered it worthwhile. anyways thats jus me,
good luck and lets know how you go
G