Regional Snowfall Index (RSI)

The Northeast Snowfall Impact Scale (NESIS)

Overview

While the Fujita and Saffir-Simpson Scales characterize tornadoes and hurricanes respectively, there is no widely used scale to classify snowstorms. The Northeast Snowfall Impact Scale (NESIS) developed by Paul Kocin and Louis Uccellini of the National Weather Service (Kocin and Uccellini, 2004) characterizes and ranks high-impact Northeast snowstorms. These storms have large areas of 10 inch snowfall accumulations and greater. NESIS has five categories: Extreme, Crippling, Major, Significant, and Notable. The index differs from other meteorological indices in that it uses population information in addition to meteorological measurements. Thus NESIS gives an indication of a storm's societal impacts. This scale was developed because of the impact Northeast snowstorms can have on the rest of the country in terms of transportation and economic impact.

NESIS scores are a function of the area affected by the snowstorm, the amount of snow, and the number of people living in the path of the storm. The diagram below illustrates how NESIS values are calculated within a geographical information system (GIS). The aerial distribution of snowfall and population information are combined in an equation that calculates a NESIS score which varies from around one for smaller storms to over ten for extreme storms. The raw score is then converted into one of the five NESIS categories. The largest NESIS values result from storms producing heavy snowfall over large areas that include major metropolitan centers. For details on how NESIS scores are calculated at the National Climatic Data Center, see Squires and Lawrimore (2006).

NESIS Calculations
Table 1: NESIS categories, their corresponding NESIS values, and a descriptive adjective:
CategoryNESIS ValueDescription
11—2.499Notable
22.5—3.99Significant
34—5.99Major
46—9.99Crippling
510.0+Extreme
Table 2: Ranks 52 high-impact snowstorms that affected the Northeast urban corridor.
Rank Start End NESIS Category Description Map
1993-03-12 1993-03-14 13.20 5 Extreme view
1996-01-06 1996-01-08 11.78 5 Extreme view
1960-03-02 1960-03-05 8.77 4 Crippling view
2003-02-15 2003-02-18 7.50 4 Crippling view
1961-02-02 1961-02-05 7.06 4 Crippling view
1964-01-11 1964-01-14 6.91 4 Crippling view
2005-01-21 2005-01-24 6.80 4 Crippling view
1978-01-19 1978-01-21 6.53 4 Crippling view
1969-12-25 1969-12-28 6.29 4 Crippling view
10  1983-02-10 1983-02-12 6.25 4 Crippling view
11  1958-02-14 1958-02-17 6.25 4 Crippling view
12  1966-01-29 1966-01-31 5.93 3 Major view
13  1978-02-05 1978-02-07 5.78 3 Major view
14  2007-02-12 2007-02-15 5.63 3 Major view
15  2010-02-23 2010-02-28 5.46 3 Major view
16  1987-01-21 1987-01-23 5.40 3 Major view
17  1994-02-08 1994-02-12 5.39 3 Major view
18  2011-01-09 2011-01-13 5.31 3 Major view
19  2011-02-01 2011-02-03 5.30 3 Major view
20  2014-02-11 2014-02-14 5.28 3 Major view
21  2010-12-24 2010-12-28 4.92 3 Major view
22  1979-02-17 1979-02-19 4.77 3 Major view
23  1972-02-18 1972-02-20 4.77 3 Major view
24  1960-12-11 1960-12-13 4.53 3 Major view
25  2010-02-04 2010-02-07 4.38 3 Major view
26  2013-02-07 2013-02-10 4.35 3 Major view
27  1969-02-22 1969-02-28 4.29 3 Major view
28  2010-02-09 2010-02-11 4.10 3 Major view
29  2006-02-12 2006-02-13 4.10 3 Major view
30  2014-01-29 2014-02-04 4.08 3 Major view
31  1961-01-18 1961-01-21 4.04 3 Major view
32  2009-12-18 2009-12-21 3.99 2 Significant view
33  1966-12-23 1966-12-25 3.81 2 Significant view
34  1969-02-08 1969-02-10 3.51 2 Significant view
35  1958-03-18 1958-03-21 3.51 2 Significant view
36  1967-02-05 1967-02-08 3.50 2 Significant view
37  1982-04-06 1982-04-07 3.35 2 Significant view
38  2013-12-30 2014-01-03 3.31 2 Significant view
39  2013-03-04 2013-03-09 3.05 2 Significant view
40  2013-12-13 2013-12-16 2.95 2 Significant view
41  2007-03-15 2007-03-18 2.54 2 Significant view
42  2000-01-24 2000-01-26 2.52 2 Significant view
43  2000-12-30 2000-12-31 2.37 1 Notable view
44  1997-03-31 1997-04-01 2.29 1 Notable view
45  2011-01-26 2011-01-27 2.17 1 Notable view
46  1956-03-18 1956-03-19 1.87 1 Notable view
47  2011-10-29 2011-10-30 1.75 1 Notable view
48  2009-03-01 2009-03-03 1.59 1 Notable view
49  1987-02-22 1987-02-23 1.46 1 Notable view
50  1995-02-02 1995-02-04 1.43 1 Notable view
51  2014-01-20 2014-01-22 1.26 1 Notable view
52  1987-01-25 1987-01-26 1.19 1 Notable view

References:

  • Kocin, P. J. and L. W. Uccellini, 2004: A Snowfall Impact Scale Derived From Northeast Storm Snowfall Distributions. Bull. Amer. Meteor. Soc., 85, 177-194
  • Squires, M. F. and J. H. Lawrimore, 2006: Development of an Operational Snowfall Impact Scale. 22nd IIPS, Atlanta, GA.