MILLS, Wyo. – With just 80 percent of the average amount of snow for this time of year currently on the ground, officials with the Bureau of Reclamation here are looking at the potential for greatly reduced inflows into the North Platte River Basin this spring.
That’s the word, anyway, in the first snowmelt forecast the agency will issue during the first part of 2018, which was released Friday, Feb. 9. A below-average run-off this spring is expected near the furthest-upstream reservoirs above Glendo Dam, perhaps as little as just 81-percent of the 30-year average, according to the report.
Total April through July runoff in the North Platte River Basin above Glendo Dam is expected to be 735,000 acre-feet, 81 percent of the 30-year average, according to the report.
“That’s consistent with what we were seeing with the snow pack,” said Mahondri Williams, chief of the Resource Management Division for the Wyoming area office of the Bureau of Reclamation in Mills. “But there’s still good carryover (water in reservoirs) from last year.
“Even though the runoff forecast is below average, we’re still expecting a full water supply,” he said. “That hasn’t changed with this forecast.”
According to a January snowpack reports from the Natural Resource Conservation Service, the areas which feed the Platte River Valley were at anywhere from 70 to slightly more than 80 percent of normal snow pack for the time of year.
But all the news is not grim. While there isn’t as much snow as there was last year at that time, the reservoirs along the North Platte still contain an abundance of water. According to the report, dated Jan. 1, Upper and Lower North Platte reservoirs were showing 147 percent and 128 percent above average storage, respectively, mostly carryover from the 2017 irrigation season.

To determine runoff forecast amounts, Bureau of Reclamation staff use a combination of historic data and computer models to compare conditions in previous years during a given timeframe with real-time conditions this year, Williams said. That provides scenarios, which are then used to issue forecasts.
“We’re looking at the past to try to predict the future,” Williams said. “Sometimes nature falls into a pattern and sometimes nature throws us a surprise.”
That’s the case this year, as nature threw something of a weather curveball, Rob Cox, science and operations officer for the National Weather Service in Cheyenne, said in January. The lack of precipitation this year is due to a La Nina weather pattern currently sitting over the entire region, he said.
“This year, we weren’t anticipating to be in a La Nina pattern,” Cox said. “It’s kind of difficult to predict. Usually these patterns are very seasonal, tending to happen from the fall through the spring time frame.”
Reduced water amounts in the river system have the potential to trigger allocations, limiting the amount of water available to the irrigation districts and, inevitably, to the producer to raise crops. But Jeff Cowley, North Platte River coordinator for the Interstate Streams division of the Wyoming State Engineer’s Office, said chances of allocations being issued this year are slight at best.
Cutoff for allocations is 1.1 million acre feet. As of Jan. 31, storage content in the North Platte Reservoirs amounts to 2,085,600 af, 135 percent of the 30-year average, according to the Bureau of Reclamation report. The total conservation storage capacity of the North Platte Reservoir System is approximately 2,815,900 af.
“That’s good for everyone in the North Platte drainage,” Cowley said. “As Mother Nature helps us out a little bit, we can avoid a call this year.”
And these numbers are only early estimates, based on current conditions, Williams and Cowley said. Historically, the North Platte River Basin has experienced similar conditions as recently as 2016, Williams said, when the snowpack tracked well below normal for most of the winter, only to experience a huge turnaround in the spring.
“In March (2016, snowpack) went from below average at the beginning of the month to almost average by the end of the month,” he said. “Then, with good precipitation in May, the overall inflow ended up being well above average for the year.
“There’s still a lot of season remaining, still additional months of snow accumulation,” Williams said. “We’ll just have to wait and see. The coming months are still very important months for accumulations in the snow pack.”
Cowley agreed: “There’s still just as good a chance of getting pounded with snow as there is of not getting another flake. It’s still too early to tell.”
Additional snowmelt forecast reports will be issued by the Bureau of Reclamation in March, April and May.