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Published January 25, 2011
Streamflow Forecast(for spring and summer)
Data Source(s): National Water and Climate Center
The first spring–summer streamflow forecast for the Southwest, issued on January 1, shows below-average flows for basins in the Mogollon Rim region of Arizona, above-average flows for most of the Upper Colorado River Basin, and mostly near- to below-average flows for New Mexico basins (Figure 12). Widespread and intense storms that drenched California, northwest Arizona, and Utah beginning in mid-December have helped contribute to an optimistic spring streamflow forecast for the Colorado River Basin. The dry southern regions of Arizona and New Mexico reflect the influence of La Niña events, which often deflect the storms north.
The current forecast suggest at least a 50 percent chance that inflow to Lake Powell will be about 117 percent of the 1971–2000 average for April–July. The forecast also indicate a 70 percent chance that Lake Powell inflow will be slightly more than the historical average of 7.7 million acre-feet. Forecasts for the Salt River and Upper Gila, on the other hand, call for only a 30 percent chance that streamflows during the January–May period will be equal to or greater than 90 and 77 percent or average, respectively.
In New Mexico, the January 1 forecast shows the majority of the state on pace for a significantly below-average runoff season. The only average or above-average forecast is for the San Juan River Basin; this forecast reflects the above-average snowpack in northern New Mexico, southern Colorado, and the Upper Rio Grande. Streamflow forecasts decline south of these basins due to lower-than-average snowpack in these areas. However, it is still early in the snow season and conditions could rapidly change in Arizona, New Mexico, and across the West.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