24-Month Studies

Monthly 24-Month Study Reports present hydrological descriptions and projected operations for the Colorado River system reservoirs for the next two years. The 24-Month Study Report is a combination of a write up of recent, current and potential future operations and a listing of the 24-Month Study computer model output. The 24-Month Study computer model projects future reservoir conditions and potential dam operations for the system reservoirs given existing reservoir conditions; inflow forecasts and projections; and a variety of operational policies and guidelines. Monthly reservoir inflow forecasts and projections are produced by the National Weather Service, Colorado Basin River Forecast Center .

The 24-Month Study model is updated at the beginning of each month upon receipt of the monthly inflow forecast from CBRFC. The CBRFC reservoir inflow forecasts extend from three to seven months based on the time of year. Values used in the model beyond that are based on historic statistical averages. For most months, the CBRFC reservoir inflow forecast is only produced for the most probable (50% probability of exceedance), however for the months of August, October, January and April minimum probable (90% exceedance) and maximum probable (10% exceedance) inflow forecasts are produced by CBRFC. For these months, minimum, most and maximum probable runs of the model are conducted producing a range of potential future reservoir conditions and operations.

Reclamation has revised the format of the 24-Month Study Report beginning with the May 2021 report. The 24-Month Study report continues to provide coordinated operations for the Upper Colorado and Lower Colorado Basin reservoir operations. It now includes a coordinated introduction providing salient information for the current month.

Upper Colorado Basin hydrology summary language for major reservoirs will continue to be available in the separate basin hydrology summaries below.

It should be noted that all future conditions and operations presented in the 24-Month Studies are only projections and are subject to change as the year progresses and actual hydrology, operations and forecasts diverge from those used to produce specific 24-Month Study projections.


Please contact the Operations Group via e-mail at ResourceMgr@usbr.gov for additional questions or information.

Last Updated: 9/15/21