2-Year Probabilistic Projections


The 2-year probabilistic projection of future Colorado River system conditions are produced using the Colorado River Mid-term Modeling System (CRMMS) in Ensemble Mode. Projections extend out 24 months (the same period as the 24-Month Study) and are released monthly, typically by the 15th day of the month.

  • Initial Conditions: CRMMS is initialized with previous end-of-month reservoir elevations.
  • Hydrology: Upper Basin inflows are 30 unregulated inflow forecasts traces from the Colorado Basin River Forecast Center (CBRFC) ensemble streamflow prediction (ESP) method, which relies on observed temperature and precipitation from 1991-2020. Lower Basin inflows are the historical intervening flows from 1991-2020 that align with the ESP traces.
  • Water Demand: Upper Basin demands are estimated and incorporated in the unregulated inflow forecasts provided by the CBRFC; Lower Basin demands are developed in coordination with the Lower Basin States and Mexico.
  • Policy: 2007 Interim Guidelines, Lower Basin Drought Contingency Plan, and Minute 323 are modeled reflecting Colorado River policies.

For more detailed information about the approach to these projections, see the 2-Year Probabilistic Projections Approach page. All modeling assumptions and projections are subject to varying degrees of uncertainty. Please refer to this discussion of uncertainty for more information.


The 2-year probabilistic projections are referred to as CRMMS-ESP. Results can be explored using an interactive visualization tool that depicts projected reservoir conditions produced by CRMMS-ESP and the 24-Month Study. The interactive visualizations for Lake Powell, Lake Mead, and other reservoirs’ projected conditions are linked below:

Lake Powell and Lake Mead end-of-month elevation charts are shown below. The charts show both the CRMMS-ESP and 24-Month Study results. The gray cloud represents the full range of the CRMMS-ESP projections, with individual gray lines showing each trace within the cloud.

Projected Lake Powell end-of-month elevations from the latest CRMMS-ESP and 24-Month Study inflow scenarios.

Projected Lake Mead end-of-month elevations from the latest CRMMS-ESP and 24-Month Study inflow scenarios.

For additional information or questions, please contact us via email at: .

To be notified when updated projections are available, please email with “Add Me” as the subject.

Last updated: 2021-12-15