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Published May 23, 2012
Streamflow Forecast(for spring and summer)
Data Source(s): National Water and Climate Center
The May 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 13).
In Arizona, the last streamflow forecast was made on April 1 because the vast majority of the rain and snow that contributes to spring streamflows has already fallen by this date. On April 1, there was a 50 percent chance that the Salt, Verde, and Gila rivers would have streamflows equal to or less than 28, 41, and 7 percent of the February–May average, respectively. In New Mexico, the last streamflow forecast, issued on May 1, suggests a 50 percent chance that streamflow in the Rio Grande, measured at Otowi Bridge, will be 45 percent of average and a 50 percent chance that inflow into Navajo Reservoir will be only 44 percent of average.
In the Upper Colorado River Basin, all snow-monitoring stations are reporting below-average snowpacks, with most measuring no snow. Many stations have been persistently below average all winter. As a result, the most recent forecast issued on April 1 projected that the April–July inflow into Lake Powell would be only about 3.5 million acre-feet (MAF), or 44 percent of the 1971–2000 April–July average. In snow-dominated basins like those in the upper Colorado River, April 1 forecasts are usually 80–90 percent accurate. Also, projections for the entire 2012 water year, which extends from October 1, 2011 through September 30, 2012, call for inflow into Lake Powell to be around 5.57 million acre-feet (MAF). If this holds true, inflow will rank as the fourth lowest on record since the closure of the Glen Canyon Dam in 1963. Precipitation in coming months could increase or decrease, with the likely inflow range falling between 4.9 MAF (45 percent of average) and 6.5 MAF (60 percent of average).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 13. 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