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The Winter Storm Severity Index (WSSI) <\/span>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.<\/span><\/p>\n

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).<\/span><\/p>
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WSSI web service classification of the severity of winter weather impacts are defined as:<\/span><\/p>\n

Winter Weather Area - <\/span>Expect Winter Weather. Winter driving conditions. Drive carefully.<\/span><\/p>\n

Minor Impacts - <\/span>Expect a few inconveniences to daily life. Winter driving conditions. Use caution while driving.<\/span><\/p>\n

Moderate Impacts - <\/span>Expect disruptions to daily life. Hazardous driving conditions. Use extra caution while driving. Closures and disruptions to infrastructure may occur.<\/span><\/p>\n

Major Impacts - <\/span>Expect considerable disruptions to daily life. Dangerous or impossible driving conditions. Avoid travel if possible. Widespread closures and disruptions to infrastructure may occur.<\/span><\/p>\n

Extreme Impacts - <\/span>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.<\/span><\/p>
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The <\/span>components of the WSSI<\/span> are defined as:<\/span><\/p>\n

Snow Amount Index - <\/span>Indicates potential impacts due to the total amount of forecasted snow. Higher snow totals can inundate all forms of transportation and limit mobility, disrupt infrastructure (e.g., utilities, transportation systems, schools, businesses, delivery and medical services), and result in damage to vegetation or property. Snow climatology is accounted for as areas of the country less accustomed to snowfall may be less prepared to deal with snow, and thus may experience more severe societal impacts. Population and road network data are also considered in this component, as densely populated or heavily traveled areas are more susceptible to cascading impacts from snow.<\/span><\/p>\n

Snow Load Index - <\/span>Indicates potential impacts due to the weight of the forecasted snowfall. Increased snow loading can include significant damage to trees, vegetation, built structures, and infrastructure such as power or utility lines. Impacts associated with the physical exertion to remove wet, heavy snow are also accounted for, such as musculoskeletal strains or cardiovascular injuries. Tree type and density, the amount of leaves on deciduous trees, and wind speed are all considered in this component, in addition to snow load climatology.<\/span><\/p>\n

Ice Accumulation Index - <\/span>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. Tree type and density and the amount of leaves on deciduous trees is accounted for, in addition to population and road network data.<\/span><\/p>\n

Flash Freeze Index - <\/span>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 \u201cblack ice\u201d conditions. <\/span><\/p>\n

Blowing Snow Index - <\/span> Indicates potential impacts due to visibility reductions during active snowfall. Low visibility in snowfall can impact surface transportation and be disorienting to anyone caught outside in those conditions. Land cover is considered for this component, in addition to the duration of visibility reductions.<\/span><\/p>\n

Ground Blizzard Index - <\/span>Indicates potential impacts due to visibility reductions and snow drifts that can occur when pre-existing snow is blown or drifted by strong winds. This component addresses similar impacts (i.e., to surface transportation and to those caught outside in these conditions) to the blowing snow component, but with the distinction that the ground blizzard component is for pre-existing snowfall instead of actively falling snow. Land cover is considered for this component, in addition to the duration of visibility reductions.<\/span><\/p>
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Update Frequency:<\/span> Every 2 hours<\/span><\/p>
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Link to graphical web page: <\/span>https://www.wpc.ncep.noaa.gov/wwd/wssi/wssi.php<\/a><\/span><\/p>\n

Link to data download: <\/span>https://www.wpc.ncep.noaa.gov/wwd/wssi/gis/shp/<\/a><\/span><\/p>\n

Link to <\/span>metadata<\/a><\/span><\/p>\n

Questions/Concerns about the service, please contact the DISS GIS team.<\/span><\/p>\n

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