Hi Rockhound. Jet A-1 is probably the most commonly used jet aviation fuel worldwide and has a freezing temperature of -47c. Jet A (used in USA) freezes at -40c. There are other types as well as additives such as FSII (fuel system ice inhibitor if memory serves me right).
The point is that at airliner cruise levels the fuel will have to be warmed, particularly on long sectors at high latitudes. One common method is to use a heat exchanger between engine driven generators and fuel system. This has a dual benefit as the hot oil in the generators is cooled by the very cold fuel and the fuel absorbs the heat from the exchanger before being pumped back into the tanks, and so it goes on. On flights of 4 hours and longer, the fuel temp seems to reduce to a minimum of around -25c and then stabilise.