The Northeast Snowfall Impact Scale (NESIS)

by Anita Silverman

NESIS ranks the severity of an East Coast snowstorm based on snowfall amount and the population of the affected areas. NESIS provides a quantitative measure of the snowstorm's potential socio-economic impact, compared with storms of the past, and assigns each large storm with one of the five categories—notable, significant, major, crippling or extreme. 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.

 

An example from the 2006-2007 winter season is the complex storm that struck the mid-Atlantic and New England on February 14 and 15, 2007. This storm was classified as "major," or a Category 3 on The Northeast Snowfall Impact Scale (NESIS).

 

The strong storm produced widespread snowfall across the mid-Atlantic, bringing the heaviest amounts to interior regions of the Northeast. Freezing rain, sleet and a thick coating of ice brought widespread power outages in Washington , D.C. , Maryland and Virginia . Snowfall amounts exceeded 20 inches throughout large parts of New York and New England , but the heavily populated urban corridor—from Washington , D.C. , to Boston —received less than 5 inches(Figure 1). While the highest amounts were outside the largest urban areas of the Northeast, the storm's ranking as Category 3 reflects its massive size and the high snowfall totals in less populated areas of the region.

 

Figure 1 - Total Snowfall (in.), Feb 12-15, 2007

Figure 1 - Total Snowfall (in.), Feb. 12-15, 2007

 

NESIS was jointly developed by Paul J. Kocin, a former winter weather expert at The Weather Channel and Louis W. Uccellini, director of the NOAA National Centers for Environmental Prediction in Camp Springs, Md. Thomas R. Karl, director of the NOAA National Climatic Data Center, led the effort to make NESIS operational.

 

NESIS scores are calculated at the National Climatic Data Center and 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 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.

 

 

NESIS categories, 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

 

Top 10 high-impact snowstorms (since 1950)

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

(click on hyperlinked dates for map of storm)

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.

 

The Northeast Snowfall Impact Scale (NESIS)