I've got a 2000 Audi A6 2.7 Turbo, that recently emitts huge smoke, in below freezing temperatures, from the exhaust pipes, today for over 20 miles till it stopped.
My guess is something is sticking to prevent a proper gas mix.
Anybody out there care to guess?

Smokey

 

Sounds like a frozen / clogged craankcase breather line. Pressure builds in the crankcase and forces oil out various seals. If it happens again, pull over, open the hood and open the oil filler cap to see if it releases a bunch of pressure.

 

Smoke color.
May be no correlation to anything.
I would assume you know which smoke means which but
White is water, Blue/ gray is oil, black is fuel, any other color is not normal.