As others have said, mash indoors. I do it year round. I use an electric bucket heater (about $25 from any farm supply store) in my HLT. For early morning brewing, I even hook that up to an appliance timer for early in the morning so I can get up, mash in, and then go take my shower and eat some breakfast. Don't even have to put my pants on until I go outside for the boil (prudish neighbors get upset

).
All kidding aside, this process has all sorts of advantages. The biggest of which is consistency of your process. Your grain temp and mash tun temp are the same every brew. You don't have to recompute your strike temperature every time and you don't have to second guess the changing temperature loss.
Wayne