The Utility of the ECMWF Extreme Forecast Index to Gain Lead Time & Forecaster Confidence on High Impact Flooding Events in Alaska

Flooding is a significant natural hazard in Alaska. These events are often driven by extreme precipitation events/atmospheric rivers that pose substantial risks to communities, infrastructure, and ecosystems. Additionally, many communities require substantial lead time in order to take protective actions ahead of impactful weather events; thus it is necessary to provide timely, and accurate information to decision-makers at lead times often longer than a typical National Weather Service (NWS) flood Watch/Warning time frame. This study leverages the European Centre for Medium-Range Weather Forecast’s (ECMWF) Extreme Forecast Index (EFI) for precipitation to enhance the lead time and accuracy of NWS messaging ahead of heavy precipitation events in Alaska. The study found a high correlation between high EFI values and flooding events up to 144 hours before the event. By leveraging the EFI for precipitation, forecasters can have increased confidence in issuing flood products or enhanced messaging to decision makers well in advance of any developing impacts