The Winter Storm Severity Index – A Tool to Better Communicate Impacts During Flash Freeze and Winter Storm Events (342)

Cathy Zapotocny, NOAA/NWS, Omaha/Valley, NE



The Winter Storm Severity Index - A Tool to Better Communicate Impacts During Flash Freeze and Winter Storm EventsA variety of winter weather occurs across Nebraska and Iowa, impacting public safety, transportation, schools, commerce, and power. The Winter Storm Severity Index (WSSI) is a prototype, graphical, impacts-based index that uses forecast, static, and derived data in a GIS environment. The WSSI incorporates National Weather Service (NWS) National Digital Forecast Database (NDFD) forecasts of six-hourly snow, ice, and liquid precipitation accumulation, and hourly forecasts of wind gusts and temperature. Daily national snow analysis of snow depth, snow pack temperature, and snow water equivalent from the National Operational Hydrologic Remote Sensing Center are used along with non-forecast datasets that include land-use designations and gridded annual snowfall climatology. These meteorological and non-meteorological inputs are employed to calculate an individual predictive index for snow load, snow amount, blowing snow, ground blizzard, ice accumulation, and flash freeze. The WSSI represents the maximum value of these component indices in terms of an impacts-based descriptor level limited, minor, moderate, major, or extreme. Meteorologists at the NWS at Omaha/Valley are routinely tasked with evaluating complex winter weather situations and communicating the weather forecast and impacts to the public and our partners. These forecasts are made hours to several days in advance with the goal of reducing the impacts of winter weather by the public and our partners making informed decisions. The WSSI supports this goal by leveraging the NWS gridded NDFD database in an innovative way to provide additional situational awareness to forecasters and allows them to better communicate societal impacts to emergency managers and other partners.This presentation will focus on what the WSSI is, what has changed for 2017-2018, examples of its use this past season, explore feedback gathered from core partners, and identify current strengths and areas of potential improvement.