Leveraging Probabilistic Data and ArcGIS Online Dashboards to Enhance Extreme Precipitation Forecasts in Alaska

Over the past decade, fatal debris flow events in Alaska's south and southeastern coastal areas have highlighted the need for improved precipitation forecasting. These events typically feature heavy rainfall, rising freezing levels, and strong winds driven by atmospheric rivers. Given southern coastal Alaska's temperate rainforest climate, characterized by substantial annual precipitation, it is crucial to contextualize heavy precipitation forecasts.

Traditionally, forecasters in Alaska rely on Annual Recurrence Intervals (ARI) to contextualize observed precipitation due to the lack of a flash flood guidance product. Recent efforts have focused on displaying ARI information for observed precipitation at gauge sites across the state, enhancing situational awareness during heavy precipitation events. However, no such context currently exists for quantitative precipitation forecasts.

To address this gap, we have developed a Probabilistic Extreme Precipitation Forecast tool. This tool uses the National Blend of Models (NBM) Probabilistic Quantitative Precipitation Forecasts (PQPF) 6 and 24 hour accumulations out to 5 days lead time to display percent exceedance of ARI thresholds at known gauge locations on an ArcGIS Online dashboard. This approach allows forecasters to assess the impact of precipitation events more confidently and provide solid numerical probabilities of extreme precipitation to further the NWS vision of providing probabilistic Impact Decision Support Services (IDSS) to emergency management decision-makers.