I just checked your weather and your high is, OMG, -2°C and low is -8°C
(ours is a high of 22°C - but we have a drought). You weren't kidding about 'colder' weather!
I think your readings are normal, especially if all the tires are doing this.
Our alloy wheels might be a bit porous and I make a habit of checking my tire pressure monthly around the first of the month and they're usually down one or two psi. I no longer keep mine at 60psi but do run them at 40 psi - a little over the recommended 36 psi (248kPa).