From: "William Wright (Dr)" <W.Wright@BoM.GOV.AU>
To: Mark Williams <Mark.Williams@BoM.GOV.AU>
Cc: "'synoptic_discussion@bom.gov.au'" <synoptic_discussion@BoM.GOV.AU>
Subject: [synoptic_discussion] Northwest cloudbands

>>Another question, why have we NOT had any northwest cloud bands with such
>>deep troughs off the WA coast?

Interesting observation, Mark. I seem to recall the same thing happening
during the autumn/early winter of 1994 (an El Nino year, by the way), and
this serves to illustrate the point that tropical-extratropical cloudbands
require both tropical and midlatitude conditions to be favourable - and the
two do NOT necessarily always coincide, even on climate time-scales. I don't
have an answer to your question, but it may lie in moisture fields (perhaps
related to SSTs) over the tropical oceans surrounding Australia (mainly, but
not entirely, the tropical Indian Ocean), and/or low level wind-fields over
these oceans, which would influence moisture uptake from the boundary layer.

Regards all,

Bill W.