The Northeast Snowfall Impact Scale (NESIS)

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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 of The Weather Channel 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).

Table 1: NESIS categories, their corresponding NESIS values, and a descriptive adjective:

Category	NESIS Value	Description
1	1—2.499	Notable
2	2.5—3.99	Significant
3	4—5.99	Major
4	6—9.99	Crippling
5	10.0+	Extreme

Table 2: Ranks 35 high-impact snowstorms that affected the Northeast urban corridor.

(click on hyperlinked dates for map of storm)

Rank	Date	NESIS	Category	Description
1	Mar 12-14, 1993	13.20	5	Extreme
2	Jan 6-8, 1996	11.78	5	Extreme
3	Feb 15-18, 2003	8.91	4	Crippling
4	Mar 2-5, 1960	8.77	4	Crippling
5	Feb 2-5, 1961	7.06	4	Crippling
6	Jan 11-14, 1964	6.91	4	Crippling
7	Jan 21-24, 2005	6.80	4	Crippling
8	Jan 19-21, 1978	6.53	4	Crippling
9	Dec 25-28, 1969	6.29	4	Crippling
10	Feb 10-12, 1983	6.25	4	Crippling
11	Feb 14-17, 1958	6.25	4	Crippling
12	Jan 29-31, 1966	5.93	3	Major
13	Feb 5-7, 1978	5.78	3	Major
14	Feb 12-15, 2007	5.63	3	Major
15	Jan 21-23, 1987	5.40	3	Major
16	Feb 8-12, 1994	5.39	3	Major
17	Feb 18-20, 1972	4.77	3	Major
18	Feb 17-19, 1979	4.77	3	Major
19	Dec 11-13, 1960	4.53	3	Major
20	Feb 22-28, 1969	4.29	3	Major
21	Feb 12-13, 2006	4.10	3	Major
22	Jan 18-21, 1961	4.04	3	Major
23	Dec 23-25, 1966	3.81	2	Significant
24	Feb 8-10, 1969	3.51	2	Significant
25	Mar 18-21, 1958	3.51	2	Significant
26	Feb 5-8, 1967	3.50	2	Significant
27	Apr 6-7, 1982	3.35	2	Significant
28	Mar 15-18, 2007	2.55	2	Significant
29	Jan 24-26, 2000	2.52	2	Significant
30	Dec 30-31, 2000	2.37	1	Notable
31	Mar 31 - Apr 1, 1997	2.29	1	Notable
32	Mar 18-19, 1956	1.87	1	Notable
33	Feb 22-23, 1987	1.46	1	Notable
34	Feb 2-4, 1995	1.43	1	Notable
35	Jan 25-26, 1987	1.19	1	Notable

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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. 22^nd IIPS, Atlanta, GA.