Grass-Cast: A New, Experimental Grassland Productivity Forecast Expanding to the Southwest Region

Grass-Cast growing season forecast August 13, 2019

Every spring, ranchers face the same difficult challenge—trying to guess how much grass will be available for livestock to graze during the upcoming summer. Since May 2018, an innovative new Grassland Productivity Forecast or “Grass-Cast” has been helping producers in the Northern Great Plains reduce this economically important source of uncertainty. Grass-Cast is now expanding to the Southwest region and will soon be available to producers in New Mexico and Arizona.

This experimental grassland forecast is the result of a collaboration between the Agricultural Research Service (ARS), a part of the U.S. Department of Agriculture (USDA); National Drought Mitigation Center (NDMC); Colorado State University and the University of Arizona.

Grass-Cast uses over 30 years of historical data about weather and vegetation growth—combined with seasonal precipitation forecasts—to predict if rangelands in individual counties are likely to produce above-normal, near-normal, or below-normal amounts of vegetation for grazing.  The program’s accuracy improves as the growing season unfolds, so it should be consulted more than just once during the growing season. Grass-Cast’s maps are updated every two weeks to incorporate newly observed weather data and emerging trends in grazing conditions.

Grass-Cast provides ranchers and land managers with an indication of what productivity is likely to be in the upcoming growing season relative to their own county’s more than 30-year history. Ranchers and land managers will need to combine the forecast information with their knowledge of local soils, plant communities, topography and other conditions as part of their decision-making process. Since Grass-Cast cannot decipher between desirable forage species and undesirable forage species, it is important for producers to know what proportion of a pasture is occupied by weeds, and how those weeds respond to rain (or lack of rain). Grass-Cast also gives ranchers a view of rangeland productivity in the broader region to help with larger-scale decision making, such as determining where grazing resources might be more plentiful if their own region is at risk from drought.

Producers should not rely on Grass-Cast as a sole source for making management decisions. Similarly, public land managers should not use Grass-Cast as a sole source of information for setting stocking rates, determining turnout dates, or for other aspects of lease agreements, allotments or permits.

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

Project Contact: Dannele Peck, Director of the USDA Northern Plains Climate Hub, at dannele.peck@ars.usda.gov or 970-744-9043