The 24-Month Study projects future Colorado River system conditions using single-trace hydrologic scenarios simulated with the Colorado River Mid-term Modeling System (CRMMS) in 24-Month Study Mode. The Most Probable and Probable Minimum 24-Month Studies are released monthly, typically by the 15^th day of the month. The Probable Maximum 24-Month Study is released alongside other 24-Month Studies in January, April, August, and October.

• Initial Conditions: The 24-Month Study is initialized with previous end-of-month reservoir elevations.
• Hydrology: In the Upper Basin, the first year of the Most Probable inflow trace is based on the 50^th percentile of Colorado Basin River Forecast Center (CBRFC) forecasts and the second year is based on the 50^th percentile of historical flows. To represent dry and wet future conditions, the Minimum Probable and Maximum Probable traces use the 10^th and 90^th forecast percentiles in the first year and the 25^th and 75^th percentiles of historical flows in the second year, respectively. The Lower Basin inflows are based only on historical intervening flows that align with the Upper Basin percentiles.
• 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, 2024 Supplement to the 2007 Interim Guidelines, Lower Basin Drought Contingency Plan, and Minute 323 are modeled reflecting Colorado River policies. For modeling purposes, simulated years beyond 2026 assume a continuation of the 2007 Interim Guidelines including the 2024 Supplement to the 2007 Interim Guidelines (no additional SEIS conservation is assumed to occur after 2026), the 2019 Colorado River Basin Drought Contingency Plans, and Minute 323 including the Binational Water Scarcity Contingency Plan. With the exception of certain provisions related to ICS recovery and Upper Basin demand management, operations under these agreements are in effect through 2026. Reclamation initiated the process to develop operations for post-2026 in June 2023, and the modeling assumptions described here are subject to change.

Reclamation will continue to carefully monitor hydrologic and operational conditions and assess the need for additional responsive actions and/or changes to operations. Reclamation will continue to consult with the Basin States, Basin Tribes, the Republic of Mexico and other partners on Colorado River operations to consider and determine whether additional measures should be taken to further enhance the preservation of these benefits, as well as recovery protocols, including those of future protective measures for both Lakes Powell and Mead.

For more detailed information about the approach to the 24-Month Study modeling, see the CRMMS 24-Month Study Mode page. All modeling assumptions and projections are subject to varying degrees of uncertainty. Please refer to this discussion of uncertainty for more information.

Projections

The latest 24-Month Study reports for each study can be found at the links below:

• Most Probable 24-Month Study
• Probable Minimum 24-Month Study
• Probable Maximum 24-Month Study

Archived 24-Month Study results are also available. Descriptions of the 24-Month Study hydrologic scenarios are also documented in Monthly Summary Reports. Lake Powell and Lake Mead end-of-month elevation charts are shown below.

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

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