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Published March 21, 2012
Streamflow Forecast(for spring and summer)
Data Source(s): National Water and Climate Center
The March 1 spring-summer streamflow forecast for the Southwest shows a 50 percent chance that all but one basin in the upper and lower Colorado River and Arkansas watersheds will be below average (Figure 12). Only a few basins in the Rio Grande are expected to have above- or near-average flows.
In Arizona, the likelihood that the Salt, Verde, and Gila rivers will have streamflows of 37, 31, and 27 percent of the February–May average, respectively, is 50 percent. Although widespread and copious rain and snow fell in many basins in mid-March, this boost likely will not substantially increase spring streamflows. The La Niña helped deliver a dry spell that extended from late December to mid-March. This protracted period has all but ensured below-average streamflows for most of the Southwest, unless powerful and frequent late winter storms soak the region.
Winter precipitation in New Mexico has been more frequent and has delivered more rain and snow than in Arizona, but most streamflow forecasts also project below-average flows. There is a 50 percent chance that the March–July flow in the Rio Grande will be between 70 and 89 percent of average. On the other hand, near-average flows are expected in the Canadian River in northeast New Mexico. 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 67 percent of the 1971–2000 average for April–July, or about 5.3 million acre-feet. This is a slight increase from forecasts issued on February 1 but is about 2.5 million acre-feet below average. The forecast also indicates only about a 10 percent chance that Lake Mead inflow will be above average. Last winter’s exceptionally high streamflows, which delivered about 7 million acre-feet more than average to Lakes Mead and Powell, will help 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
- 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