funny thing, today I was with my teacherand he showed me how to do a faggot weld....he took about a 10x.125 x1.25 piece of rusty old left over mild steel, curfed the ends, bent it around to a circle and got the spot he wanted to weld aligned and clear of slag....then he heated it to a orange and sprinkled borax on it stuck it in his busted up forge...left it get yellow and shiny brought it out and hammered medium to light and repeated the process 2x ...it welded ...we then stuck it in the slack tub which was froze and hoped it didnt "pop"
it was maybe 25 degrees outside...he said "its welded but I wouldnt hang from it"....so my conclusion is it dont matter what the temp is except in the forge...it was a propane forgethat is in need of a repair desperatly so also confirms anything I heard from guys "you cant do it with propane" wrong!