Grass-Cast: An Experimental Grassland Productivity Forecast Expands to Arizona and New Mexico


Final Grass-Cast estimates of production for 2020 summer growing season in AZ & NM

Every spring, ranchers face the same difficult challenge—trying to guess how much grass will be available for livestock to graze during the upcoming season. Since May 2019, an innovative Grassland Productivity Forecast known as “Grass-Cast” has been helping producers in both the Northern and Southern Great Plains reduce this economically important source of uncertainty. Grass-Cast is an experimental model that generates map-based forecasts of grassland productivity, offering a potential new tool in the drought-planning toolbox for ranchers and rangeland managers.

Officially released for the Southwest in Spring 2020, Grass-Cast is now available to producers throughout Arizona and New Mexico. It is the result of a collaboration between the U.S. Department of Agriculture  Agricultural Research Service, the USDA’s “Climate Hubs” (a collaboration of USDA agencies that helps provide regional delivery of tools and information to agricultural producers), and Natural Resources Conservation Service. (NRCS)Also partners in the project are the National Drought Mitigation Center, Colorado State University, and the University of Arizona. Funding from USDA ARS and NRCS, as well as NDMC and the U.S. Geological Survey, has supported Grass-Cast’s expansion to the Southwest region.

Grass-Cast provides three “what-if” scenarios that show how much grass might grow during the upcoming season depending on whether precipitation is above, near, or below-normal.

The model uses well-known relationships between historical weather and grassland production. It combines current weather data and seasonal climate outlooks (from the National Oceanic and Atmospheric Administration’s Climate Prediction Center) with a well-trusted grassland model known as “DayCent,” to predict total biomass (lbs/acre) at the peak of the growing season for individual 6-mile by 6-mile areas, compared to the area’s 36-year average. Grass-Cast also provides a wider view across the region to help livestock managers see where grazing resources might be more plentiful if their own region is at risk of drought.

Example Grass-Cast maps for the Southwest (made on August 11, 2020), which estimate peak standing biomass (lbs/acre), compared to an area’s historical (36- yr) average, for the summer growing season under three different precipitation scenarios: Above Normal (left), Near Normal (center), or Below Normal (right)

Grass-Cast is an optional tool that managers can use to develop well-informed expectations about the upcoming growing season. It can be used in the design of proactive drought management plans, trigger dates, stocking dates, and grazing rotations. But producers and agencies should not rely on Grass-Cast as a sole source for making management decisions. Nor should they look at Grass-Cast just once during the growing season. The grassland productivity forecasts are updated every two weeks to incorporate newly observed weather data and emerging trends in growing conditions. For this reason, Grass-Cast’s accuracy improves as the growing season unfolds, which is why it should be consulted more than just once during the season.  


Visit the Grass-Cast website ( for updates, the latest static and zoomable maps, and other resources.

Grass-Cast contact: Dannele Peck, Director of the USDA Northern Plains Climate Hub,

USDA Southwest Climate Hub contact: Emile Elias, Director,

Authors: Dannele Peck, Emile Elias and Lauren Kramer