Weather system clustering provides a high-level summary of regional meteorological conditions. Most quantitative clustering schemes focus on precipitation alone, which does not sufficiently describe the meteorological conditions driving hydroclimate variability. This study presents a weather system classifier, WAC-hydro, which extends the capability of existing weather systems to predicting hydroclimate variability. It identifies 12 daily weather anomaly modes in the U.S. Pacific Northwest Puget Sound region during 1981-2020. Our analysis indicates that the influence of modes of climate variability (ENSO and Madden-Julian Oscillation) on regional precipitation can be well approximated by their modulation on the weather anomaly modes. Within each weather system type, local factors such as topography only play a secondary role in the hydrologic variability. The weather modes highlight two types of flood-inducing regional weather conditions, one causing floods by inducing positive precipitation anomalies and the other causing floods through combined precipitation and temperature-induced rain-on-snow effect.