Usually the coldest part of Greater Manchester for minimum temperatures is around the area where the coldest temperature of last winter occured so probably around the area of Woodford near Stockport, the cold filters down off the Pennines over that particular area which sharply falls in elevation, also it is not in the busy city centre, the city centre and nearby being low down should be a frost bowl but with the warmth from the thousands of buildings it obviously isn't.
The snowiest part of Greater Manchester is most of the time reserved to the NE part, particularly the villages of Saddleworth, the villages of Diggle and Denshaw would be a sure fire bet for the snowiest award. The boroughs of Oldham, Rochdale and Tameside coming not far behind., also these areas are usually colder with the maximum temperatures throughout the year on average in Gtr Manchester. We have a very varied climate to say the least!