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Inflows drop: Statewide forecasts reduced in April 1 forecast

by Wyoming Livestock Roundup

Casper – In a press release issued April 4, the Bureau of Reclamation (BuREC) Wyoming Area Office says their April 1 forecast indicates what everyone already suspected – spring snowmelt runoff for the North Platte River Basin will be below average.
    In addition to that basin, Wyoming Area Office Acting Area Manager Lyle Myler says Boysen Reservoir and the Wind River Basin will receive adequate runoff, and Buffalo Bill Reservoir and the Shoshone River drainage will be right at average.
    “If there’s a basin doing ok with snowpack, it would be the Shoshone River Basin,” says Myler. “Above Buffalo Bill Reservoir, the snowpack was tracking right at or a little above average when we forecast on March 1, but things have trended down and snowpack has dropped off.”
    As of April 1, BuRec forecast an inflow for Buffalo Bill of 700,000 acre-feet for the period from April through July.
    “That is a reduction from March 1, when we forecast 780,000 acre-feet, because of the snowpack dropping below average,” says Myler, adding that the expected 700,000 acre-feet, compared to the 30-year average from 1982 through 2011, is about 103 percent of average. Average runoff in that period has been 679,000 acre-feet, and the highest runoff in those 30 years was in 2011, with 1,230,000 acre-feet.
    “There’s quite a difference between what we just forecast and what we got last year,” says Myler.
Boysen just below average
    In the drainage above Boysen Reservoir, Myler says that, once again, he’s seen snowpack that has dropped consistently throughout the basin.
    “Based on the Natural Resources Conservation Service (NRCS) SnoTel reports for Boysen and the Wind River Basin, a couple weeks ago we were 90 percent of average, and on April 2 we’d dropped to 74 percent of average,” he notes.
    “The April 1 forecast for runoff that we believe will reach Boysen Reservoir is 550,000 acre-feet, and last month with better snowpack we forecast 650,000 acre-feet,” says Myler. “In the last 30 days our forecast has dropped 100,000 acre-feet.”
    The current forecast is 96 percent of the 30-year average of 574,000 acre-feet of inflow from April through July.
    “The caveat is that, even with below-average expected runoff, we had really good carryover in Boysen Reservoir, so as far as the water supply right now we’re in good shape, because of that carryover storage,” adds Myler.
North Platte expects low inflow
    Myler calls the North Platte River Basin the “ugly” part of the story.
    “We’ve seen a similar thing with the snowpack as in the other basins. The basin above Seminoe Reservoir hasn’t had very good snowpack this winter at all. A couple weeks ago it was at 72 percent of average, and as of April 2, with the warm, hot weather, it dropped to 54 percent of average,” says Myler. “Our April 1 forecast for inflow to Seminoe Reservoir is 350,000 acre-feet, which compares to our forecast of 550,000 acre-feet last month.”
    In 2011 the inflow to Seminoe was an all-time record – 1,969,000 acre-feet of water.
    Myler says the snowpack numbers this winter and spring are tracking similar to their pattern in 2002, which resulted in the lowest inflow on record – 118,000 acre-feet of water flowing into Seminoe over the four spring runoff months.
System remains full
    As with Boysen Reservoir, Myler says the good news on the North Platte is the carryover storage from the record inflow in 2011.
    “The reservoir system is still pretty full,” he says. “All the storage space on the North Platte River system holds 2,841,000 acre-feet of water, and at the end of March we had 2,350,000 acre-feet in storage, and that’s 140 percent of average for March. The system is about 83 percent full.”
    “Even with the poor forecasted inflow, we should be in pretty good shape as far as water supplies this summer,” he reassures.
    “Our last storage point on the system is Guernsey Reservoir, and we shut the gates at the end of September and we haven’t made any releases,” notes Myler. “Because of the significant reduction in that forecast for inflows, we don’t anticipate releasing water early this year. Last year we were thinking we’d release water from Guernsey early to make space for runoff, but with the way things look right now we won’t make early releases. We’ll hang onto it all and deliver it for irrigation purposes.”
Looking ahead
    “The bad news is that forecasts and inflows are dropping, but we had good carryover storage and we’ll be able to manage through this year,” says Myler. “If things stay the way they are with below average inflows, irrigators and water users may want to think about measures to conserve water for future years. Who knows what the next few years will bring, but we’ve had a history of three or four above average water years, then when things drop off we get two or three below average years to follow.”
    Myler says information he heard from the Riverton office of the National Weather Service indicates above normal temperatures and below normal precipitation could continue throughout the summer.
    “Two years ago in 2010, about this time, things turned and we got some wet rainy weather and the outlook changed. It’s still early, and things could be dry or they could change on us, so right now we’re conserving as much water as possible in case we get a below average inflow year, and we’re keeping an eye on the weather conditions and snowpack, and if things turn wet we’ll be moving water to make room for whatever runoff we may get,” he says.
    Christy Martinez is managing editor of the Wyoming Livestock Roundup and can be reached at

North Platte: the forecast details
    As of April 4, the April through July runoff in the North Platte Basin above Glendo Dam was expected to be 535,000 acre-feet or 55 percent of the 30-year average of 967,700 acre-feet.
    Approximately 350,000 acre-feet (45 percent of average) of the runoff is expected to enter Seminoe Reservoir, with an additional 50,000 acre-feet (82 percent of average) provided to Pathfinder Reservoir from the Sweetwater River, and the balance of 135,000 acre-feet (99 percent of average) coming from the basin between Pathfinder Reservoir and Glendo Reservoir.  
    The total storage for the North Platte Reservoir System as of March 31 is 2,349,781 acre-feet, which is 140 percent of the 30-year average of 1,677,600 acre-feet. The total conservation storage capacity of the North Platte Reservoir System is approximately 2,841,000 acre-feet.

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