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Published April 27, 2011
Streamflow Forecast(for spring and summer)
Data Source(s): National Water and Climate Center
Last winter’s La Niña event left a dry imprint on the Southwest. The spring–summer streamflow forecast issued by Natural Resources Conservation Service for the Southwest issued on April 1 predicts below-average flows for basins in the Mogollon Rim region of Arizona and New Mexico basins and near- to above-average flows for most of the Upper Colorado River Basin (Figure 12). These forecasts are based principally on snow accumulation in the mountains from which most of the water originates. Precipitation during March was well below normal throughout all basins in Arizona and New Mexico. In Arizona, snowpack levels were well below average in all of the basins as of April 1, with most measurement sites void of snow. A winter storm in early April boosted snowpack and precipitation totals in many basins in the Southwest, including the Upper Colorado River Basin, resulting in higher streamflow projections for the Colorado River.
The April 1 forecasts projects a 50 percent chance that inflow to Lake Powell will be about 120 percent of the 1971–2000 average for April–July, or 9.5 million acre-feet, an increase over last month’s forecast of 113 percent of average. Forecasts for the Salt and Upper Gila rivers, on the other hand, call for very low probabilities that flows will be near average. Forecasts indicate a 50 percent chance that streamflow in the Salt and Verde rivers during the April–May period will be equal to or less than about 15 and 43 percent of average, respectively.
In New Mexico, the April 1 forecast shows the majority of the state on pace for well below-average runoff. Forecasts indicate a 50 percent chance that the Rio Grande streamflow at Otowi Bridge will be only 48 percent of average for the April–July period. Forecasts for the Upper Gila and Pecos rivers call for a 50 percent chance that streamflow will be at or below 23 and 35 percent, respectively, for the same period.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 March and April, and for New Mexico between March 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
- Dan Ferguson, CLIMAS Program Director
- Gregg Garfin, Founding Editor, Institute of the Environment
- Zack Guido, CLIMAS Associate Staff Scientist
- Gigi Owen, CLIMAS Assistant Staff Scientist
- Nancy J. Selover, Arizona State Climatologist
- Jessica Swetish, CLIMAS Publications Assistant
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