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The Winter Storm Severity Index (WSSI) combines weather forecast data from the National Digital Forecast Database (NDFD) with non-meteorological and climatological data to produce an impact-based forecast product for winter weather. It creates an easily consumable graphical depiction of anticipated societal impacts for a variety of winter hazards (e.g., snow, ice), and is designed to aid in situational awareness for potential winter impacts.
The WSSI classifies impacts as “minor,” “moderate,” “major,” and “extreme.” A “winter weather area” classification is used to denote areas where a winter hazard is expected to occur, but is not anticipated to impact daily life. The WSSI updates every 2 hours and provides forecasts for 24-hour periods out to 72 h (i.e., Day 1, 2, and 3), as well as a 72-hour forecast encompassing the full forecast period (i.e., Days 1-3).
WSSI web service classification of the 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 components of the WSSI are defined as:
Snow Amount Index - Indicates potential impacts due to the total amount of forecasted snow or the snow accumulation rate. Increasing snow totals can inundate transportation and limit mobility, disrupt infrastructure (e.g., utilities, transportation systems, schools and businesses, delivery and medical services), and damage vegetation or property. Increasing snow rates can also overwhelm transportation by limiting visibility and reducing the ability for roadway maintenance crews to keep up with rapid accumulations. This index accounts for climatology, such that regions of the country that typically experience less snowfall will generally have a higher impact severity level for a given snowfall than for regions that typically experience more snowfall. Densely populated or urban areas receive an increase to the impact severity level.
Snow Load Index - Indicates potential impacts due to the weight of the forecasted snowfall. Impacts can include damage to trees, vegetation, built structures, and infrastructure (e.g., utility or power lines), in addition to cardiovascular or muscular injuries due to the physical exertion associated with clearing heavy snow loads. This index accounts for land use, forest type and density, and 50-year mean recurrence intervals of snow load.
Ice Accumulation Index - Indicates potential impacts due to ice accretion on flat surfaces (e.g., roadways, sidewalks) and/or elevated surfaces (e.g., tree limbs, overhead wires). Impacts can include disruptions to transportation, pedestrian slips, falls, or injuries on icy surfaces, and physical damage to property, vegetation, and infrastructure. Additional weight on overhead utility lines or tree limbs can cause them to sag or snap, resulting in the potential for widespread power outages or blocked roadways. Wind is included as an enhancing factor for impacts on elevated surfaces, and densely populated or urban areas receive an increase to the impact severity level.
Flash Freeze Index - Indicates potential impacts due to the rapid freezing of water-covered surfaces (e.g., roadways, sidewalks). Impacts can include disruptions to transportation and injuries to motorists or pedestrians encountering these “black ice” conditions.
Blowing Snow Index - Indicates potential impacts due to blowing and drifting snow. Impacts can include transportation disruptions from limited visibility, and these conditions can be dangerous to motorists and disorienting to anyone caught outside in those conditions. This index accounts for land use. For example, heavily forested areas will have lower blowing snow potential than open areas.
Ground Blizzard Index - Indicates potential impacts due to strong winds blowing or drifting pre-existing snow cover. Impacts can include transportation disruptions from limited visibility, and these conditions can be dangerous to motorists and disorienting to anyone caught outside in those conditions. Pre-existing snow cover data along with forecasted winds are used to model the ground blizzard. This index accounts for land use. For example, heavily forested areas will have lower ground blizzard potential than open areas.
Update Frequency: Every 2 hours
Link to graphical web page: 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.