said by shrug :
Windchill isn't even relevant.
Well, I think it could be, even for alkizmo's bathroom. There is a temperature gradient from room temperature (let's just say 60F) at the inside wall of alkizmo's bathroom to -30F at the outside of the same wall because that room is exposed as he described it. If the wall and the rest of the room is well insulated, there will only slight thermal transfer from inside to outside; if the insulation is poor, then there will be a significant transfer from inside to outside. But further, in a still wind, the -30F outside is not instantaneous at the wall boundary, as whatever heat is coming from the inside will radiate into the outside air, dissipating as it gets further away from the wall. For sure, at -30F, the dissipation will be rapid and the air temperature will be at ambient -30F within a very short distance. However, with a stiff wind, that few inches of temperature gradient from the outside wall temperature to the exact point of -30F will be swept away leaving a colder boundary at the wall surface. The wall will then radiate whatever latent heat it has that much faster, which will, in turn, draw more heat out of the inside of the room if it can, i.e., if the insulation is poor and consequently a potential for thermal transfer through the wall. The water pipes, being inside the wall and closer to the cold face, will freeze sooner on a windy night than a still night of the same nominal temperature.