I typically avoid going on the ice if it's higher than -3'C (27F) during the afternoon - especially if it's sunny - as I find it just chews up the ice. I'm a little more lenient during the mornings and evenings when the sun isn't as prominent like goblue already stated. No way I would have anyone skating on it @ 37/38 let alone 17 people. I would also be worried about someone getting hurt on the soft ice.
Making Backyard Rinks from 1999-2015
Twitter: @kevmac_5 or @macisaac_odr
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