How Much Snow Fell in NYC?

Just ran across this snowfall map of the Boxing Day Blizzard in NYC:

Purple = more than 20 inches. Click to enlarge. 

Now, take a look at the "worst case scenario" forecast from this very blog posted at 8:50 am the 25th: 

The red over Manhattan is 18" and the gray/pink tinted color inside the red is 20" or more. The storm was described as a "nightmare." Gusts were forecast in the 40 to 60 mph range.