Wind days are the ones that get people hurt. The problem isn't always the tree you're cutting, it's the widow-maker shifting above you, or a hung tree dislodging because the canopy is moving. My personal rule is no felling if there's sustained wind above about 15-20 mph and I'll back that down further if I'm working in standing dead or in areas with a lot of previous disturbance where there's more debris risk. Even at low wind speeds, checking the canopy above the landing zone before you're committed in the cut is non-negotiable. What wind conditions make you walk away from a tree?