USA Snowfall forecast for Blizzard of 2013 just got bigger. What changed?

Much of the region covered by blizzard warnings had been expected to get 18 to 24 inches of snow. Now the figure is 24 inches-plus. Features called snow bands are figuring into the calculus for Blizzard of 2013.

Jim Cole/AP

Overnight, predicted snowfall totals from the now-building Blizzard of 2013 jumped higher than the previous estimate, to above the two-foot mark. What happened?