Image caption
The skill of seasonal (rolling 3-month average) precipitation forecasts (bright blue line) is often significantly better than statistics say we could expect due to chance (indicated by a Heidke skill score above 0, which is shown by the dashed line). But on average (dark blue line), skill has remained relatively modest for several decades. The Precipitation Prediction Grand Challenge aims to speed up the pace of improvements. Climate.gov graph, adapted from Climate Prediction Center data.