Currently, the system time zone is used for determining local time. The software assumes your weather spot is also in your time zone, which works fine for 99% of use cases, but if you want to build a rotating display showing weather in other places, things go a bit wrong.
For example, a computer in the UK displaying weather in Australia will never show a "good laundry day" because your 10am time to put the laundry out is in UK time, which is evening in Australia.
Need to double check how iCal times are handled as well, make sure we are getting the times as UTC so they are plotted right.