Grass-Cast helps ranchers determine how much grass they will have this summer

This question is on the top of ranchers’ minds right now. Overall, it was dry last fall, over the winter and so far this spring. How much grass will there be this summer? Directly related to that question, how many head of livestock can I graze this year? How long can they graze?

Oh, for a crystal ball. Since one is not likely to drop out of the sky, we can use the next best thing: Grass-Cast.

Grass-Cast, or Grassland Productivity Forecast, has over 30 years of historical data about weather and vegetation growth. It compares that data with current year precipitation to create three production forecast maps. Each map indicates the expected grass growth based on above-normal, near-normal, or below-normal rain. Grass growth is color coded from 30% above to 30% below normal. In the past, these predictions were county based. However, this year a user can zoom to 6-mile by 6-mile areas.

The first maps are released in early April and are highly speculative. However, as time goes by and actual rainfall is recorded, the biweekly maps become more accurate and useful. Particularly when paired with what is known about the timing of grass growth.

Extension research across the plains has found that grass growth is best predicted by precipitation received 30 days prior to the peak growth period. There is a point when the grass hits peak leaf growth and shifts to making seed and food storage for the winter. This shift occurs somewhere between June 15 and July 15. The 30-day period prior would therefore be May 15 to June 15.

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