How Predictable Was the Extreme Precipitation Preceding the May 2019 Arkansas River Floods?

Abstract In May 2019, unprecedented extreme rainfall over the central United States (US) facilitated severe flooding along the Arkansas River. The well‐documented relationship between atmospheric rivers (ARs) and central US heavy precipitation motivated investigation into AR relevance to this event and its predictability on extended timescales. AR conditions coinciding with the extreme precipitation indicate ARs contributed to the Arkansas River flooding, while poisson weighted forecast probabilities of SHiELD ensemble hindcasts show both the ARs and extreme precipitation were predictable at 2 week leads. Comparison of precursory atmospheric conditions between the top and bottom five performing ensemble members reveal the top performers developed a Rossby wave train over the North Pacific, which promoted AR‐favorable conditions downstream and facilitated better forecasts of precipitation than the bottom performers. Results suggest cross‐Pacific Rossby wave trains can provide a forecast of opportunity for extended predictability of ARs and extreme precipitation over the central US.