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Grass-Cast: Grassland Productivity Forecast

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. An innovative Grassland Productivity Forecast or “Grass-Cast” is now helping producers in the Great Plains and Southwest regions reduce this economically important source of uncertainty.

Grass-Cast indicates for ranchers and other grassland managers whether productivity (pounds per acre) is likely to be above-normal, near-normal, or below-normal in the upcoming growing season relative to the 30+ year history of their local area (individual 6-mile x 6-mile grid cells). Grass-Cast is first published in the spring (typically beginning in late April) and then updated every two weeks with newly observed weather data. It therefore becomes more accurate as the growing season unfolds and should be consulted throughout the growing season. 

Ranchers and rangeland managers will need to combine the information from Grass-Cast with their knowledge of local soils, plant communities, topography, grazing history, and other conditions as part of their decision-making process. Similarly, public land managers should not use Grass-Cast as a sole source of information for setting stocking rates, turnout dates, or other aspects of lease agreements, allotments, or permits.

Grass-Cast cannot tell the difference between desirable forage species and undesirable forage species. So, it is important for grassland managers to know what proportion of a pasture is occupied by weeds, and how well those weeds respond to rain (or lack of rain) compared to the desirable species. Monitor these different vegetation types to see if one is responding to the weather better than the other and adjust Grass-Cast’s productivity estimates accordingly.

Grass-Cast also does not account directly for local management practices, such as grazing intensity in previous years. Producers should therefore monitor pastures to see which ones respond better (or worse) to the weather and adjust Grass-Cast’s productivity estimates upward (or downward) accordingly.

Grass-Cast does give ranchers and other managers a broad view of grassland productivity across the Great Plains and Southwest regions. This can help identify where grazing resources might be more plentiful when their own region is at risk from drought. Grass-Cast provides forecast information only for vegetation quantity, not quality.  

Grass-Cast is a collaboration among the USDA Agricultural Research Service (ARS), the USDA Natural Resources Conservation Service (NRCS), the National Drought Mitigation Center (NDMC), Colorado State University, the University of Arizona, and the USDA Climate Hubs.

Funding for this project came from the USDA ARS and NRCS, and the National Drought Mitigation Center.


Grass-Cast uses over 30 years of historical or simulated data (1982-present) about daily weather, evapotranspiration, NDVI (a remotely sensed greenness index), and above-ground net primary productivity (ANPP, a measure of peak plant biomass). Details of the Grass-Cast model are published in journal articles, which are listed on the Grass-Cast website ( under the “FAQ” tab.


Grass-Cast (the Grassland Productivity Forecast) provides 3 maps for ranchers and other grassland managers to consider. The left-most map shows how well grassland vegetation is expected to grow if precipitation from the day the maps were made through the rest of the growing season (typically through August 31) is above-average. The middle map shows how well grassland vegetation should grow if precipitation through the rest of the growing season is near-normal. The right-most map shows how well grassland vegetation should grow if precipitation through the rest of the growing season is below-average. To determine if the three maps are equally likely, or if one map is thought to be more likely than the others, users are directed to NOAA’s Seasonal Precipitation Outlook. Within an individual map, each 6-mile x 6-mile grid cell is assigned a color. The color indicates whether grassland vegetation is expected to be X% higher or lower than that grid cell’s 30+ year history.




Researcher, Extension, Producer, Land Manager, Other

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Tool Developers:

W.J. Parton, M.D. Hartman, D. Schulte, M. Chen, S. Lutz, & W. Gao (CSU); J.D. Derner & S.J. Del Grosso (USDA-ARS); B. Fuchs (NDMC); W.K. Smith (UAZ); D. Larsen & R. Guerrero (USDA-NRCS); D.E. Peck (USDA-NPCH); E.H. Elias (USDA-SWCH); K.A. Day (Australia)