Safety-Worker,
My company prescribes a formula of 4% errror per 10 degree drop below ISA of the mean temperature layer below the aircraft (in reality we would all use ISA at altitude for that....) Therefore for 10,000 feet indicated with a temperature of ISA minus 30, you would find your altimeter overread by 1200 feet on that formula.
In addition, where the wind at the relevant MSA is forecast to be 50 knots or more, we increase the MSA by 2000 feet. In mountain wave conditions, then a vertical clearance over the highest ridge at least equal to the height of the ridge above the surrounding terrain should be selected. Memories of the Mount Fuji 707 I think...
On my type (320) inthe sphere of operations we use then these are generally of academic interest... however, I still mention the drift-down criteria as a routine in my emergency brief because the one day we will be caught out is over the alps, in a chilly northerly airmass with very strong winds, and only just make the criteria. Also, it is a self-discipline thing not to forget it, having flown big twins (and big 4-engined as well) over mountainous terrain with MSA's well above the drift-down alt regardless of temperature corrections.
Reverse will also apply.. I well remember first time flying into the Gulf and noting the point at which the rad-alt came active being well different to what it would be in Europe, all down to density altitude.
Squid