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Published April 25, 2012
Streamflow Forecast(for spring and summer)
Data Source(s): National Water and Climate Center
The April 1 spring-summer streamflow forecast for the Southwest shows a 50 percent chance that all basins in the Colorado River, Rio Grande, and Arkansas watersheds will be below average (Figure 12). In many basins, forecasts call for flows to be less than 50 percent of average, including the Upper Colorado River and Rio Grande.
In Arizona, there is a 50 percent chance that the Salt, Verde, and Gila rivers will have streamflows equal to or less than 28, 41, and 7 percent of the February–May average, respectively. These values reflect the persistence of dry conditions since January 1, which were influenced by a La Niña event that contributed to snow and rain accumulations of less than 50 percent of average in many areas.
Winter precipitation in New Mexico was slightly more frequent than in Arizona and delivered more rain and snow, but most streamflow forecasts still project below-average flows. There is a 50 percent chance that the March–July flow in the Rio Grande will be less than or equal to 44 percent of average.
All snow-monitoring stations in the Upper Colorado River Basin are reporting below-average snowpacks, with most measuring less than 50 percent of the historical average. Many stations have been persistently below average this winter. As a result, spring inflow to Lake Powell is forecast to be only about 3.5 million acre-feet, or 44 percent of the 1971–2000 April–July average. This is a substantial decrease from forecasts issued on March 1, which called for inflow to be about 5.3 MAF. Combined water storage in Lakes Mead and Powell will almost assuredly decrease this spring. However, last winter’s exceptionally high streamflows, which delivered about 7 million acre-feet more than average to Lakes Mead and Powell, will help buffer below-average flows in the Colorado River this year.Notes:
Water supply forecasts for the Southwest are coordinated between the National Water and Climate Center, part of the U.S. Department of Agriculture’s Natural Resources Conservation Service (NRCS), and the Colorado Basin River Forecast Center (CBRFC), part of NOAA. The forecast information provided in Figure 12 is updated monthly by the NWCC. Unless otherwise specified, all streamflow forecasts are for streamflow volumes that would occur naturally without any upstream influences, such as reservoirs and diversions. The coordinated forecasts by NRCS and NOAA are only produces for Arizona between January and May, and for New Mexico between January and May.
The NRCS provides a range of forecasts expressed in terms of percent of average streamflow for various exceedance levels. The forecast presented here is for the 50 percent exceedance level, and is referred to as the most probable streamflow. This means there is at least a 50 percent chance that streamflow will occur at the percent of average shown in Figure 12. The CBRFC provides a range of streamflow forecasts in the Colorado Basin ranging from short fused flood forecasts to longer range water supply forecasts. The water supply forecasts are coordinated monthly with NWCC.
For state river basin streamflow probability charts, visit: :
For information on interpreting streamflow forecasts, visit: :
For western U.S. water supply outlooks, visit: :
Southwest Climate Outlook Staff
- Michael Crimmins, UA Extension Specialist
- Stephanie Doster, Institute of the Environment Editor
- Gregg Garfin, Founding Editor, Institute of the Environment
- Zack Guido, Managing Editor, CLIMAS Associate Staff Scientist
- Nancy J. Selover, Arizona State Climatologist
- Jessica Dollin, CLIMAS Publications Assistant
- Dave Dubois, New Mexico State Climatologist
Please direct your Southwest Climate Outlook comments and suggestions to Zack Guido.
The CLIMAS Web site contains official and non-official forecasts, as well as other information. While we make every effort to verify this information, please understand that we do not warrant the accuracy of any of these materials.... Read full disclaimer