Best to find out what the rated pressure is for your tires, then use an auto-type tire gauge to take a reading and see. If you have fluid in the tires for weight, you want to roll the tire until the air filler thingie is at the top. That way there will be some air there to measure, if the stem is lower you’ll be pulling fluid out when you try to test.
I have not found weather to have any more effect on tractor tires than they do on auto tires. All loose some pressure as the temps fall.If a tire was on the low end in the summer it can easily get very low on a really cold day.
I’d trust your gut on this, if you are seeing the tire(s) as lower than before they likely are. Time to get the air tank and pressure gauge out. Oh and keep in mind, if you fill them up when it’s 0F out, you will likely need to let some air out once temps get higher. (not a bad idea for the cars too).
And I’d second BobC’s comments, low tires can be dangerous if you are using your front loader.