"Historic" is an overused word, but it applies to the blizzard that’s coming for the national capital region, large parts of which could get more than 30 inches of snow over the weekend.The National Weather Service said Washington, D.C., itself could get as much as 29 inches by Sunday night — topping the record measured in the Knickerbocker blizzard of January 1922, when 28 inches of snow fell. That storm was named for Crandall’s Knickerbocker Theatre — the roof of which collapsed under the weight of snow, killing 98 people and injuring 133 others.