Airlines routing over Tibet have to carry extra oxygen to account for the lowest safe altitude.
Flying into a weather system will see your ISA deviation go up, I’ve seen in excess of ISA +20, which means your recommended MAX ALT goes down so make sure you have a good margin before entering. The associated turbulence would warrant a decent spread between the upper and lower limits displayed on the ASI as well.
Avoid weather at your upper altitude limit with a narrow coffin corner.