One guy I worked for sent me and my helper out one day, to do a commercial rough in , it was around 5-10 degrees, with a bout a 40 mph wind out of the north , nothing real unusual. Not a tree or anything in site to block the wind, ground was frozen so hard and deep the back hoe couldn`t break thru it . Thee boss sent me to buy a couple of picks, thank GOD there wasn`t any to be had. We like to froze what time we were out there.