The Probabilistic Winter Storm Severity Index (WSSI-P) for Days 1-7 is a graphical depiction created through the use of Geographic Information Systems (GIS) by using the probabilistic winter precipitation forecast (PWPF) gridded information from the Weather Prediction Center (WPC) for winter weather elements and combining those data with non-meteorological or static information datasets (e.g., climatology, land-use, urban areas). The WSSI-P web service provides a classification of the likelihood of potential societal impacts due to expected winter hazards and their distribution using the following terminology: minor, moderate, major, and extreme. Forecasts periods are for 24 hours starting from hour 24 through hour 168.

The WSSI-P sub-components are defined as:

Snow Rate Index - Indicates potential impacts due to snowfall rate. Designated urban areas are also weighted 25% more than non-urban areas. Forecast is available for 168 hours

Snow Load Index - Indicates potential infrastructure impacts (e.g., downed trees/power lines) 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. Forecast is available for 168 hours

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. Forecast is available for 168 hours

Ice Accumulation - Indicates potential infrastructure impacts (e.g., downed trees/power lines, roads/bridges) due to combined effects and severity of ice and wind. Designated urban areas are also weighted 25% more than non-urban areas. Note that not all NWS offices provide ice accumulation information into the NDFD. In those areas, the ice accumulation is not calculated. Forecast is available for 168 hours.

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.

This Probabilistic WSSI web service is divided into the following groups of data: Overall Winter Storms, Snow Amount, Snow Rate, Snow Load, Ice Accumulation, and Blowing Snow.

The Likelihood of Potential Societal Impacts in this web service are defined as:

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.

Update Frequency: This will update 4 times a day roughly 00Z, 06Z, 12Z, and 18Z

Link to graphical web page

Link to data download (shapefile)

Link to metadata

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

Time Information:

This service is time enabled