When January nitrate was between 6 and 8 mg/L in the period of 1974-2016, annual nitrate ended up between 4.7 and 8.5, a much tighter window than the entire range of observed annual averages (0.6 to 11.7 mg/L). The overall long term annual average is 6.6 mg/L. Based on this I am predicting a below average-to-average year for Raccoon River nitrate.

Summary of the 2016 Nitrate loads in the Des Moines and Raccoon Rivers.

If Iowa continues to get wetter, which many climate experts predict, relatively modest increases in precipitation could result in disproportionately large increases in nitrate-N loads.