Grass-Cast warns of potential for challenges in grassland production in northest Colo. |

Grass-Cast warns of potential for challenges in grassland production in northest Colo.

Amy Hadacek
for The Fence Post
This photo was taken about 10 miles northeast of Nunn, Colo., in Weld County.
Photo by Melissa Johnston, USDA-ARS

For ranchers and land managers in northeastern Colorado’s Weld, Morgan, Logan and Washington counties, the latest Grass-Cast prediction maps — as of May 26, 2020 — are showing early-warning signs for possible challenges in grassland production this year.

The Grass-Cast maps suggest that from now through August, above-average precipitation is needed across most of these counties in order to result in normal grassland production (-5% to +5% of the 38-year average).

Calculating Grassland Production:

However, if average precipitation occurs, rather than above-average, grassland production predictions fall to -5% to -15% below-normal,” said Justin Derner, research leader for the U.S. Department of Agriculture’s Agricultural Research Service Rangeland Resources and Systems Research Unit.

What would be expected if precipitation ends up being below-average from now through August? “This large region would be predicted to produce 15% to 30% less than normal grassland production (pounds per acre of grassland vegetation this summer for grazing), Derner said. “Thus, only if above-average precipitation occurs from now through August would ranchers and land managers not face a forage deficit.”

It’s important to note, Grass-Cast cannot tell the difference between grasses, forbs or shrubs. “It also cannot tell the difference between palatable and weedy species,” said Dannele E. Peck, director of the Northern Plains Climate Hub of the USDA-ARS in Fort Collins, Colo. “Grass-Cast lumps all these types of vegetation together to provide a general estimate of how much more or less pounds per acre we expect a site to produce during the upcoming growing season, relative to its long-term average.”


“For areas south of U.S. Highway 50, it’s been very dry. For Bent, Otero, Crowely and Las Animas counties, they are running under 40 percent of (what would be) normal for the four month period of 2020. Even though the four month precipitation for southeastern Colorado is normally about 3 inches, so far many locations have received 1 inch,” said Kyle Mozley, meteorologist with the National Weather Service in Pueblo, Colo.

Along the Interstate 25 corridor, from Huerfano County, north into El Paso County, conditions are faring a bit better. “Precipitation through the January to April time-frame is between 50-75 percent of normal. So better, but not great,” Mozley said.

Regarding soil moisture, the top 1 meter of soil is very dry.

Late May to the first of June has seen an uptick in precipitation for parts of southern Colorado. The mountains have had near daily hit and miss heavy rain, and some made it off the mountains and into the I-25 corridor, Mozley said. Mother Nature has delivered a whammy in some areas of Colorado, beginning with April’s freezing temperatures (many locations in the teens and 20s for several days), killing off plants that had already started to leaf out due to a warm February through March. The peach crop on the western slope suffered losses.

Comparing this winter/spring snowpack with snowpack from one year ago, “The peak snowpack in the Arkansas and Rio Grande basins this winter was been very near average,” said Tony Anderson, service hydrologist for the National Weather Service in Pueblo. “That was only about two-thirds as much as last year which was near a historic high. The snowpack on June 2, was near the historically low values of 2018.” Anderson pointed out the tremendous change in snowpack in one month’s time, from April 1 to May 1, as snow melted rapidly this spring.


In addition to recently including — as of May 2020 — all of New Mexico and Arizona, Grass-Cast also covers much of the Southern Plains, including north Texas, western Oklahoma and western Kansas, and much of the Northern Plains, such as eastern Colorado, eastern Wyoming, eastern Montana, western North Dakota, western South Dakota and western Nebraska.

Grass-Cast is a tool that can assist ranchers and grassland managers in the Colorado Plains with forage planning and productivity. It provides three different scenarios for the current rangeland conditions and estimates how rangeland would be affected by: normal precipitation, above normal or below normal precipitation.

“With average or below-average precipitation, ranchers and land managers in eastern Colorado will need to be proactively managing for a shortage in forage,” Derner said. “Contingency planning should be underway for this shortage with options including: (1) earlier removal of grazing animals from pastures, especially for yearling cattle, (2) locating additional forage for grazing or hay, (3) early weaning of calves from cows, and (4) strategizing for culling of animals from the base cow herd.”

Ranchers and land managers can contact their local, regional and state Extension range specialists for more information. Ranchers can also reach out to their nearest USDA Service Center to learn about drought programs and assistance from FSA and Natural Resources Conservation Service.

An area receiving just 50 percent of normal precipitation, means just half of what they normally receive. Or, if an area received 25 percent of normal precipitation, that means they received a quarter of what they normally receive, by this time.

A lack of soil moisture makes it difficult for rangeland grasses to meet their evapotranspiration needs (moving enough water from soil, through the roots and out their leaves to support photosynthesis and growth). “Evapotranspiration in eastern Colorado has been below normal this spring and summer, associated with plant stress and reductions in growth,” Peck said.


The Climate Prediction Center recently issued its June, July and August outlook, forecasting below normal precipitation from northern New Mexico into the western half of Colorado, into Wyoming and Montana. Eastern Colorado has slightly more favorable chances for normal precipitation.

Temperature-wise, above-normal summer warmth is predicted from Colorado into Wyoming and Montana, with even warmer temperatures expected for southwest Colorado.

It appears there will be a late start to the monsoon season, which is the reversal of the wind pattern that typically brings thunderstorm activity northward into the Rockies.

As far as the monsoon dates, “The OLR (Outgoing Longwave Radiation weather computer model) I use to track Equatorial Rossby Waves off the African Coast, is finally showing these ERs arriving after July 28 and peaking around Aug. 5,” said Mozley. “The ERs are a primary monsoon trigger, especially for eastern Colorado. They move off the African Coast, and into the Gulf of Mexico, allowing moisture to move northward into the eastern Colorado Plains.”

New this year: instead of using county views, Grass-Cast features a closer, more micro-scale perspective, zooming into a view of six miles by six miles.

“When we first shared Grass-Cast publicly in 2018, the first improvement often requested was to make it closer to a ranch-level scale. In 2019-2020, we were able to improve the spatial resolution (pixels) to roughly six miles by six miles,” Peck said. “Although this still isn’t quite ranch-level, it does allow Grass-Cast to capture more of the spatial variation that occurs across a county, especially large counties.”

The Grass-Cast team in May launched Grass-Cast maps for Arizona and New Mexico. These southwest-area maps were just posted to the website during the week of Memorial day, making it publicly available in those states.

“Even though the spring forecast only became available a few days before the end of the spring season, it’s still useful to see Grass-Cast’s final production estimates for the spring season. No model is 100 percent accurate. Stakeholders can let the Grass-Cast team know how accurate they are compared to conditions they see out on the ground,” Peck said.

Grasslands in New Mexico and Arizona tend to green-up in spring, dry down in early summer, and then green-up a second time when the monsoon season arrives later in the summer. “So, the Grass-Cast team decided they needed to develop two separate models,” Peck said. ”One for the spring growing season, and a different one for the summer growing season, available the second week of June.” ❖

— Hadachek is a freelance writer who lives on a farm with her husband in north central Kansas and is also a meteorologist and storm chaser. She can be reached at