Snake River Jackson Hole Wyoming Fishing Report

(Friday April 5, 2019)

Subject:  2019 Upper Snake River Operations Update

Purpose:  The purpose of these Operation Updates is to provide information regarding Reclamation’s operations as the season progresses.  The operations outlined in this update are based on the best data available at the time and are subject to change as new information becomes available.  For additional information and resources, please visit our website at:  https://www.usbr.gov/pn/hydromet/uppersnake/ .

Summary

The Upper Snake reservoir system is currently 83% full (3,338,896 acre-feet out of 4,045,695 acre-feet). Official water supply forecast the April-July runoff period have been finalized and the information is included in the table below. The forecast for the next 7-10 days indicate persistent precipitation accompanied by cooler than normal temperatures. The cool temperatures and precipitation will likely increase snow-water equivalent above 8,000’ and catalyze runoff in the low to mid elevation bands. Willow Creek and Little Wood basins are expected to observe notable increases in streamflow during the next week. Operational adjustments will be made based on the latest information, and more changes can be expected as reservoir operators gauge the reaction of the runoff to the forecast conditions.

Jackson Lake is projected to maintain the current release until inflow exceeds outflow in the next 2-3 weeks. USGS measured the discharge below the dam, and the new gauge height shift correction computes a flow approximately 85 cubic feet per second (cfs) lower than the previous. The physical discharge from the reservoir was not changed.

Palisades Reservoir is drafting on a trajectory consistent with current estimates for required flood control levels in early May. Palisades Dam’s current discharge is projected to be maintained for the next 3-10 days, or as conditions permit to achieve appropriate progress towards required flood control targets. However, increases to discharge in the next week cannot be ruled out at this point.

Ririe Reservoir has stored approximately 220 AF over the last week. Snow-melt above the reservoir has been increasing and is projected to continue doing so. Relatively cool temperatures so far this spring have kept the above average snowpack in place, and reclamation suspects the runoff period has been condensed versus there being a reduced volume. The ripened snow pack and associated runoff will potentially exhibit volatility in relation to temperatures and precipitation trends over the next 2-3 weeks. Cooler temperatures will lessen the impact of rain on snow, but if warmer temperatures develop quickly, the inflow magnitude will increase accordingly. Considering this, increases to Ririe’s release can reasonably be expected next week.

Island Park Reservoir is expected to maintain the current release until inflow exceeds outflow, and reservoir storage has increased to approximately 108,000 – 110,000 acre-feet.

American Falls Reservoir discharge was reduced by approximately 750 cfs to manage reservoir levels. The Upper Snake Field Office projects American Falls to be near full the first week of May.

Little Wood Reservoir is projected to maintain the current release for the next 7-10 days.

Reservoir levels, reservoir discharge and river flows can be monitored on the USBR Hydromet page here: https://www.usbr.gov/pn/hydromet/

The Upper Snake “teacup” diagram which provides a graphical overview of system conditions can be accessed here:  https://www.usbr.gov/pn/hydromet/burtea.html