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Forecasts
Published February 23, 2011

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 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). Widespread and intense storms that drenched California, northwest Arizona, and Utah in mid-December have contributed 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. In January, most of New Mexico and Arizona received scant precipitation; it was the driest January on record for New Mexico, according to the NOAA-Climate Prediction Center.

The most current forecast for Arizona suggests a 50 percent chance that inflow to Lake Powell will be about 113 percent of the 1971–2000 average for April–July, or 9 million acre-feet, which is a slight decrease from the forecast issued on January 1. Forecasts for the Salt River and Upper Gila, on the other hand, call for very low probabilities that flows will be near average.  Forecasts indicated only a 30 percent chance that streamflow in the Salt and Upper Gila rivers during the February–May period will be equal to or greater than about 50 and 37 percent of average, respectively.

In New Mexico, the February 1 forecast shows the majority of the state on pace for a 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 change rapidly.

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 February and April, and for New Mexico between February 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.

Streamflow Forecast

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