The Winter Storm Severity Index (WSSI) is created by screening the National Digital Forecast Database (NDFD) for winter weather elements and combining those data with non-meteorological or static information datasets (e.g., climatology, land-use, urban areas). It creates a graphical depiction of anticipated overall impacts to society due to winter weather.

The WSSI provides a classification of the overall expected severity of winter weather using the following terminology: “none,” “limited,” “minor,” “moderate,” “major,” and “extreme.” The WSSI is updated every 2 hours at 0100 UTC, 0300 UTC, etc… and provides forecasts for 24-hour periods covering Day 1, 2, and 3, as well as a 72-hour forecast encompassing the full Day 1-3 period.

WSSI web service classification severity of winter weather impacts are defined as:

Winter Weather Area- Expect Winter Weather, Winter driving conditions. Drive carefully.

Minor Impacts - Expect a few inconveniences to daily life. Winter driving conditions. Use caution while driving.

Moderate Impacts-Expect disruptions to daily life. Hazardous driving conditions. Use extra caution while driving. Closures and disruptions to infrastructure may occur.

Major Impacts- Expect considerable disruptions to daily life. Dangerous or impossible driving conditions. Avoid travel if possible. Widespread closures and disruptions to infrastructure may occur.

Extreme Impacts -Expect substantial disruptions to daily life. Extremely dangerous or impossible driving conditions. Travel is not advised. Extensive and widespread closures and disruptions to infrastructure may occur. Life-saving actions may be needed.

The WSSI sub-components are defined as:

Snow Load Index - Indicates potential infrastructure impacts due to the weight of the snow. This index accounts for the land cover type. For example, more forested and urban areas will show increased severity versus the same snow conditions in grasslands.

Snow Amount Index - Indicates potential impacts due to the total amount of snow or the snow accumulation rate. This index also normalizes for climatology, such that regions of the country that experience, on average, less snowfall will show a higher level of severity for the same amount of snow that is forecast across a region that experiences more snowfall on average. Designated urban areas are also weighted a little more than non-urban areas.

Ice Accumulation Index -Indicates potential infrastructure impacts (e.g. roads/bridges) due to combined effects and severity of ice and wind. Designated urban areas are also weighted a little more than non-urban areas. Please note that not all NWS offices provide ice accumulation information into the NDFD. In those areas, the ice accumulation is not calculated.

Blowing Snow Index - Indicates the potential disruption due to blowing and drifting snow. This index accounts for land use type. For example, more densely forested areas will show less blowing snow than open grassland areas.

Flash Freeze Index - Indicates the potential impacts of flash freezing (temperatures starting above freezing and quickly dropping below freezing) during or after precipitation events.

Ground Blizzard Index- Indicates the potential travel-related impacts of strong winds interacting with pre-existing snow cover. This is the only sub-component that does not require snow to be forecast in order for calculations to be made. The NOHRSC snow cover data along with forecast winds are used to model the ground blizzard. Adjustments are made based upon the land cover type. For example, heavily forested areas will have a lower ground blizzard severity than the same conditions occurring across open areas.

Link to graphical webpage: https://www.wpc.ncep.noaa.gov/wwd/wssi/wssi.php

Link to data download: https://www.wpc.ncep.noaa.gov/wwd/wssi/gis/shp/

Link to metadata

Questions/Concerns about the service, please contact the DISS GIS team.

Time Information: This service is not time enabled.