Not the overall coldest, BUT one that I remember well.

Having to change the 12" or 15" diameter cattle tank float, in Wintertime, after you accidently hit it with the axe chopping off the ice, because the LP tank heater blew-out overnight, and caused 2-3" of ice to form, on bigger rectangular cattle water tank. (water valve in bottom, center of tank, with lever and chain going up to float.)

Anyways, you got new float and eyebolt, thru center of new float.

Strip off your upper winter clothes, down to your short-sleeve T-shirt, stick your arm/s into the ice-cold water and fish around for the old float's connector, for that chain; unhook it and get new float hooked up, to that same chain. All the time, you could "feel" your arm/hand movements, under water, getting slower and slower, as the cold sunk into your extremities. 

Usually, there were 2 of us, and second person, held the first person, from falling into water tank, or slipping on ice, that might be outside the livestock water tank, also.(loose your footing)

Next, was to get those dang side-mounted LP tank heaters' pilot light lit again, with wood matches, on a 2.5 foot wire holder, and not have the cold wind blow it out, first.