Hi Slast,
Ref cold weather temperature corrections, you need to know that the definition of QNH (the altimeter setting in America and Canada). By definition there is no temperature error at airfield elevation, but an increasing one the higher above airfield elevation you get. Even in Denver if the OAT was -60 Celsius, your altimeter would read correctly at airfield elevation.
https://www.skybrary.aero/index.php/...ssure_Settings
Airfield QNH is obtained by correcting a measured QFE to sea level using ISA regardless of the temperature structure of the atmosphere. As your altimeter is calibrated using ISA, it will indicate altitude correctly at the airfield reference point. At other altitudes, the indicated altitude is likely to be in error, depending on the temperature of the atmosphere.