Using the Prototype NWS Hourly Winter Storm Severity Index (WSSI) to Complement Pathfinder

The prototype Winter Storm Severity Index (WSSI) Travel is a forecast tool in development at the Weather Prediction Center (WPC). Its algorithms take numerical weather prediction forecast data from the High-Resolution Rapid Refresh (HRRR) model and output a measure of how impactful the forecasted weather conditions could be to surface transportation. Impact guidance is hourly out to 48h every 6h, with impacts defined on a 4-tiered scale from “minor” to “extreme.” These impacts are displayed on an interactive map through the use of Geographic Information Systems (GIS), allowing forecasters to maintain situational awareness of surface-transportation hazards and impacts caused by impending winter storms. Such situational awareness is crucial to providing relevant and meaningful impact-based decision support services to NWS core partners and stakeholders. The tailored nature of WSSI Travel to surface transportation impacts provides a unique opportunity to complement Pathfinder initiatives to enhance collaboration and create a unified message of road hazards across the road weather enterprise.

Currently, WSSI Travel features several components to communicate the impacts associated with distinct hazards: snow accumulation, snow rate, ice accumulation, liquid precipitation rate, and blowing and drifting snow. Each component has been designed to reflect impacts to surface transportation, including, but not limited to: increased travel times, lane or road closures, vehicle or speed restrictions, and increased crash counts and severity. Details on these components, examples from past cases, and use-case scenarios for the product will be presented.