Four storms ranked among top 30 Northeast snows

Called the Northeast Snowfall Impact Scale (NESIS), the system was developed in 2004 by Paul Kocin and Louis Uccellini, of the National Weather Service. It's since been applied retrospectively to every major storm since 1956, and to all the big Northeast snowstorms that have occurred since the scale was developed.

The NESIS scale calculations generate an index number, which is translated into a five-level Category ranking similar to the Saffir-Simpson Hurricane Scale, including Notable, Significant, Major Crippling and Extreme.

Only two storms have been ranked as Cat. 5 "Extreme." They were the March 12-14, 1993 storm, which was given a NESIS number of 13.20; and the Jan. 6-8, 1996 storm, rated at 11.78.

Here, for comparison, with their preliminary rankings and NESIS numbers, are this winter's four biggest snowstorms. Only the three earliest had a major impact in Baltimore. And here's a link to the full list.

17. Feb. 23-29, 2010: 5.11, a Cat. 3 "Major" storm.

21. Feb. 4-7, 2010:  4.30, a Cat. 3 "Major" storm. (Map above.)

25.  Dec. 18-21, 2009:  4.03, a Cat. 3 "Major" storm.

26:  Feb. 9-11, 2010:  3.93, a Cat. 2 "Significant" storm.