we have a wind gauge at our field that can be phoned into for a reading,as well as our clubs website www.flypcc.org also has a cam and gives wind readings.
for a trainer and beginning pilot I would think 10-15 mph max for starters, when our gauge is reading 15mph not alot of guys are flying,some of the giant scale guys dont mind flying in higher wind speeds the larger planes can deal with it alot better than a trainer,I don't mind it at about a 10 mph reading, over that and it becomes more chore than fun.