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I did the marathon last year, but due to the football tournament, it was in September, and this year has reverted back to its usual slot in May. So unfortunately I cannot help with the weather, although I'm sure you could find some historical stats on the internet which would give a better idea.
As for the course (assuming it has not changed) it was pretty flat, two laps largely following the lake shoreline. The baggage/changing was a little walk from the start/finish area, but on the whole pretty fine organisation.
Hope this helps, and have a good run if you choose it!