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Published May 26, 2011
Streamflow Forecast(for spring and summer)
Data Source(s): National Water and Climate Center
This past winter’s La Niña event left a dry imprint on the Southwest. The spring–summer streamflow forecast issued May 1 by the Natural Resources Conservation Service (NRCS) for the Southwest predicts below-average flows for all basins in New Mexico and above-average flows for most of the Upper Colorado River Basin (Figure 13). These forecasts are based principally on snow accumulation in the mountains from which most of the water originates. The NRCS and the Colorado Basin River Forecast Center do not issue streamflow forecasts for Arizona after April 1. On April 1, forecasts for the Salt and Upper Gila rivers called for very low probabilities that flows will be near average. Forecasts indicated 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, many gaging stations are falling into the 10th to 24th percentiles for streamflow, which is considered below average, while some of the mainstream gages are falling into the 25th to 74th percentiles, which is considered average. Some stations along the Pecos and Upper Rio Grande tributaries are reporting well below-average flows, as are some points on the Gila and San Juan rivers. It should be noted that although snowpack levels dropped throughout April, streamflow volumes have not consistently increased accordingly, indicating sublimation and infiltration losses are occurring.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