June 6, 2008

Any Good News? Reservoirs Filling

After a slow start to the severe weather season across Nebraska, the past two weeks have brought wind damage, hail, flooding, and tornadoes. Twenty three tornadoes were observed, with significant damage reported in Kearney. The final tornado tally will undoubtedly be lower, as some of them were multiple reported events.

Precipitation summary (in inches) from May 21 through June 3, 2008 for Nebraska indicating that most of the Panhandle received less than two inches while areas of central and eastern Nebraska received 5-10 inches. (Source NOAA High Plain Regional Climate Center)

The upper air low that parked over the central Rockies before the Memorial Day weekend resulted in heavy rains and flooding across southwest, south central, west central, and central Nebraska. Observations from the NERain network indicate several 8-10 inch 24-hour precipitation totals (Figure 1), with 22 counties reporting at least 4 inches during the five-day event.

With soil water profiles full or nearly full from generous rains extending back to December, flooding will remain a problem across the eastern three-fourths of the state. Weather models have underplayed many of the recent rain events, but now indicate that thunderstorms could occur daily over the next two weeks. Thirty-day outlooks for June indicate most of Nebraska, outside of the southern Panhandle and southwest Nebraska, will see above normal precipitation and below normal temperatures.

Drought conditions continue across the Panhandle and western half of the southwest corner of Nebraska, Recent storms have improved surface moisture conditions, but have not improved levels below 18 inches. The recent rains have benefited the wheat crop, but will need to continue to boost yield prospects.

Water Reserves

The upper Platte River reservoir system has shown a positive response to the recent weather. Above normal snowpack in combination with heavy thunderstorm activity has led to strong inflows into Seminoe, Pathfinder, and Glendo reservoirs. As of June 4, Glendo Reservoir had filled its conservation pool, along with 10% of its flood pool. Seminoe was at 41.6% of capacity, up from 18% a month ago. Pathfinder was at 25.9% of capacity, up from 19% 14 days ago.

Inflows into Seminoe from snowmelt, along with recent and projected rainfall, may bring the reservoir to 60% of capacity. If the current fill rate on Pathfinder continues for another 30 days, the reservoir could approach 45% of capacity. Although these numbers appear low, they would nearly double last year's maximum capacity levels. With another normal to above normal snow season, Seminoe and Pathfinder could reach full capacity.

During much of the past month, water was released from Pathfinder at the same rate that it flowed into the reservoir. The releases were made to fill Glendo, but now that it's at capacity, water in the Pathfinder Reservoir will be held back. Glendo is releasing water at a rate of 1200 cubic feet per second which will benefit Lake McConaughy.

Combined with this inflow and high river levels downstream, McConaughy is now at 45% of capacity. The lake is nearly 6 feet higher than at this time last year and continues to fill with no water releases to ease downstream flood risks. Given current inflows from Glendo, combined late June or early July water deliveries, McConaughy may reach 50% of capacity. It is too early to tell, but we could be witnessing the turning point of Platte River reservoir system.

Allen Dutcher
Extension State Climatologist, Lincoln