Expansion of the Nebraska Winter Severity Index

Winter Severity Indices (WSIs) enable state Departments of Transportation (DOTs) to gauge hazardous winter weather on spatial and temporal scales. However, the two main limitations are: 1) they are primarily historical rather than predictive, and 2) they do not evaluate individual winter storms but rather an entire winter season. In consultation with the Nebraska Department of Transportation (NDOT), the Nebraska Winter Severity Index (NEWINS) provided a new, independent framework for assessing a winter season’s severity by categorizing winter storms. However, like most WSIs, it was a historic tool and was not predictive. Translating the NEWINS categorial framework into predictive modeling would provide immense value to NDOT’s operations. Additionally, expanding the NEWINS to include other in-storm weather hazards, such as freezing rain and blowing snow, and post-storm hazards like drifting snow, would provide further benefit to NDOT.

In this study, newly developed predictive NEWINS algorithms have been interpolated using the National Digital Forecast Database (NDFD), which is used by the National Weather Service (NWS) to produce gridded forecasts. The new and expanded NEWINS provides spatial probabilistic maps up to 72 hours in advance for precipitation type, ice accumulation, blowing snow, and drifting snow. Time series for NEWINS, and its new components, can be extracted anywhere statewide. Several case studies have been reviewed to test and verify the accuracy of these components.

The translation from historic to predictive NEWINS has offered a new way of looking at WSIs. Specifically, such WSIs can now capture weather hazards beyond only the period of precipitation and assess forecast model changes over time. The spatial and temporal capabilities of the newly expanded NEWINS heavily benefit NDOT’s winter maintenance operations and decision support services. Moreover, this framework is complementary to ongoing NWS efforts to modify its Winter Storm Severity Index and ongoing conversations regarding initiatives such as Pathfinder.