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Published February 22, 2012
Streamflow Forecast(for spring and summer)
Data Source(s): National Water and Climate Center
The spring–summer streamflow forecast for the Southwest, issued on February 1, shows a 50 percent chance that all basins in the upper and lower Colorado River watershed and Arkansas basin will be below average (Figure 12). Only a few basins in the Rio Grande are expected to have above-average flows.
In Arizona, the likelihood that the Salt, Verde, and Gila rivers will have streamflows of 37, 40, and 49 percent of the February–May average, respectively, is 50 percent.
Although widespread and copious rain and snow soaked many mountain regions during November and most of December, dry and warm conditions have since largely prevailed. These conditions are expected to continue, mostly part because the La Niña event is expected to persist into spring. The La Niña also is influencing forecasts in New Mexico. There is a 50 percent chance that the March–July flow in the Rio Grande, measured at Otowi Bridge, and the Gila River, measured near Virden, will be 79 and 52 percent of average, respectively. On the other hand, near-average flows are expected in the Pecos River and above-average flows are forecast for the Mimbres River, largely because early winter snows dumped precipitation in these regions. Streamflow forecasts are issued every month for New Mexico and every two weeks for Arizona. The forecasts become progressively more accurate as the winter progresses.
In the Upper Colorado River Basin, spring inflow to Lake Powell is forecast to be about 64 percent of the 1971–2000 average for April–July, or about 3.2 million acre-feet. The forecast also indicates only 10 percent chance that Lake Powell inflow will be 108 percent of average. Last winter’s exceptionally high streamflows, which increased combined storage in Lakes Mead and Powell by about 7 million acre-feet between April and July—about 2 million acre-feet more than average—will 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
- 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