Tires: nitrogen filled tires, nitrogen filled tires, frigid weather

Question
Dear Barry;
Why am I losing pressure on my nitrogen filled tires in cold weather on a 2008 jeep liberty with a tpms.-20 seems to be the starting point,when they achieve 45kps.

Answer
Frank,

First, you are aware that all gases lose pressure when the temperature drops, including nitrogen? (in spite of what you may have heard)  The principle is called the Ideal Gas Law.  This means that if you set the pressure of your tires when it is warm, they will underinflated when it is cold.  So you should overinflate your tires in winter weather so you don't have to yop up in the frigid weather.  About 1 psi for every 10°F drop.