Regional Snowfall Index
The Regional Snowfall Index (RSI) is a scale used by NOAA to assess the societal impact of winter storms in the eastern two-thirds of the United States and classify them into one of six categories. The system was first implemented in 2014, and is a replacement for the Northeast Snowfall Impact Scale (NESIS) system which the National Climatic Data Center (NCDC) began using in 2005. The NCDC has retroactively assigned RSI values to almost 600 historical storms that have occurred since 1900.
| Category | RSI value | Description | |||
| Five | 18.0+ | Extreme | |||
| Four | 10–18 | Crippling | |||
| Three | 6–10 | Major | |||
| Two | 3–6 | Significant | |||
| One | 1–3 | Notable | |||
| Zero | <1.0 | Nuisance | |||
Storms are ranked from Category 0 "Nuisance" to Category 5 "Extreme" on the scale. The impact of the storms is assessed in six different regions of the United States: the Northeast, Northern Rockies and Plains, Ohio Valley, South, Southeast, and Upper Midwest.
The index makes use of population and regional differences to assess the impact of snowfall. For example, areas which receive very little snowfall on average may be more adversely affected than other regions, and so the index will grant storms in those regions higher severity.