Malannie D. Hartman William J. Parton Sasha C. Reed Justin D. Derner Darin K. Schulte Elise S. Gornish David J.P. Moore Emile Elias Dannele E. Peck Brian A. Fuchs William K. Smith Emilio Aguilar-Cubilla 2025 <p><span>Here, we present a first assessment of the US Department of Agriculture’s (USDA) “Grass-Cast Southwest,” which is a forecasting tool for rangeland aboveground net primary productivity (ANPP) for the southwest region of the United States. Our results show that ANPP forecasts in early April were relatively close to the observation-based ANPP estimates in late May for all years evaluated (</span><span class="italic">R</span><span>&nbsp;=&nbsp;0.6–0.9). The relatively high predictability of spring rangeland productivity in this region is likely because it is strongly driven by antecedent winter/early spring precipitation. Conversely, the first summer forecasts produced in June did not consistently predict the final observation-based ANPP estimates in late August (</span><span class="italic">R</span><span>&nbsp;=&nbsp;−0.5–0.7), likely because summer rangeland productivity in this region is highly dependent on variable, less predictable precipitation from the North American Monsoon (NAM). Antecedent El Niño Southern Oscillation (ENSO) indices could be used to improve Grass-Cast Southwest performance in both the spring and summer. The ENSO</span><span class="sub">JFM</span><span>&nbsp;(January–March) index was significantly positively correlated with rangeland productivity during the spring season, whereas ENSO</span><span class="sub">MAM</span><span>&nbsp;(March–May) was significantly negatively correlated with rangeland productivity during the summer season.</span></p> application/pdf 10.1017/dry.2025.10013 en Cambridge University Press Grass-Cast Southwest: A seasonal rangeland productivity forecast for the southwestern United States article