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. CRMMS Ensemble Mode is driven by an ensemble of monthly unregulated streamflow forecasts developed by the National Weather Service Colorado Basin River Forecasting Center (CBRFC) using the Ensemble Streamflow Prediction (ESP) method. Results from CRMMS run with ESP are referred to as CRMMS-ESP.

  • Initial Conditions: CRMMS is initialized with previous end-of-month reservoir elevations.
  • Hydrology: Upper Basin inflows are 30 unregulated inflow forecasts traces produced by the CBRFC using the 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.
  • Drought Response Actions: CRMMS projections contain actions undertaken with the 2022 Drought Response Operations Plan, 2022 Glen Canyon Dam operational adjustment, and the 2023 operations described in the 24-Month Study.
    • The 2022 Drought Response Operations Plan includes an additional release of 500 kaf from Flaming Gorge from May 2022 through April 2023.
    • The reduction of releases from Lake Powell from 7.48 maf to 7.00 maf in water year 2022 will result in a reduced release volume of 0.480 maf that normally would have been released from Glen Canyon Dam to Lake Mead as part of the 7.48 maf annual release volume, consistent with routine operations under the 2007 Interim Guidelines. The reduction of releases from Glen Canyon Dam in water year 2022 (resulting in increased storage in Lake Powell) will not affect future operating determinations and will be accounted for “as if” this volume of water had been delivered to Lake Mead. Lake Powell and Lake Mead operations are modeled as if the 0.480 maf had been delivered to Lake Mead for Lake Powell operating tier and condition determination purposes for the U.S. Lower Basin and for Mexico.
    • Because the 2022 operations were designed to protect critical elevations at Lake Powell, Reclamation will implement Lower Elevation Balancing Tier operations in a way that continues to protect these critical elevations, or preserves the benefits of the 2022 operations to protect Lake Powell, in water year 2023 and 2024. Specifically, Reclamation modeled operations as follows:
      • The Glen Canyon Dam annual release is initially set to 7.00 maf, and in April of the given year Reclamation will evaluate hydrologic conditions to determine if balancing releases may be appropriate under the conditions established in the 2007 Interim Guidelines;
      • Balancing releases will be limited (with a minimum of 7.00 maf) to protect Lake Powell from declining below elevation 3,525 feet at the end of December; and
      • Balancing releases will take into account operational neutrality of the 0.480 maf that was retained in Lake Powell under the May 2022 action. Any Lake Powell balancing release volume will be calculated as if the 0.480 maf had been delivered to Lake Mead in WY 2022.

For more detailed information about the approach to these projections, see the CRMMS Ensemble Mode 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 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.

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

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Last updated: 2023-01-30