A Subjective Evaluation of the Winter Storm Severity Index

The Winter Storm Severity Index (WSSI) is a prototype National Weather Service (NWS) product that demonstrates the spatial distribution of forecasted societal impacts due to winter storms. Once fully operational, it will allow NWS offices to improve communication to partners, including emergency managers, highlighting potential societal impacts. The WSSI will also be useful for the media and public to distinguish regions that may have more significant impacts, leading to a more Weather Ready Nation. The WSSI contains five impact severity levels (limited, minor, moderate, major, and extreme) and six sub-components (blowing snow, flash freeze, ground blizzard, ice accumulation, snow amount, and snow load).

This study first focused on the distribution of each forecasted sub-component and severity level in the WSSI Archives. A count of the number of days containing each sub-component and severity level determined which sub-component(s) was forecasted for the greatest number of days at each severity level. Severity level percentages were also calculated for each sub-component by dividing by the total number of days and dividing by the total number of severity level cases. The second part of this study consisted of a subjective evaluation of the WSSI. Local Storm Reports and the National Centers for Environmental Information (NCEI) Storm Events Database were utilized to collect data on property damage costs, power outages, snowfall values, etc. This data was then used to determine if a forecasted region of impact was miscategorized, underdone, overdone, or verified appropriately. The results from this analysis will be shown with general trends noted. In addition, suggestions were made to further improve the WSSI for future operational use.