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Published April 27, 2011
Precipitation Outlook(May 2011–October 2011)
Data Source(s): NOAA-Climate Prediction Center (CPC)
The NOAA–Climate Prediction Center (CPC) forecasts equal likelihood of near-average, above-average, and below-average precipitation in the Southwest during through October
(Figures 10a–d). This equal chances forecast is based in part on the difficulty in projecting the monsoon, which typically begins around July 1 and ends in late September. As the monsoon approaches, more accurate forecasts will be available. In the mean time, there is some indication that the spring and summer will continue to be warm and dry: the very low soil moisture conditions that extend across much of the Southwest may reduce the amount of water vapor returned to the atmosphere by evaporation, limiting storm formation. The current soil conditions result from the La Niña-influenced dry winter.
These outlooks predict the likelihood (chance) of above-average, average, and below-average precipitation, but not the magnitude of such variation. The numbers on the maps do not refer to inches of precipitation.
The NOAA-CPC outlooks are a 3-category forecast. As a starting point, the 1971–2000 climate record is divided into 3 categories, each with a 33.3 percent chance of occurring (i.e., equal chances, EC). The forecast indicates the likelihood of one of the extremes—above-average (A) or below-average (B)—with a corresponding adjustment to the other extreme category; the “average” category is preserved at 33.3 likelihood, unless the forecast is very strong.
Thus, using the NOAA-CPC precipitation outlook, areas with light green shading display a 33.3–39.9 percent chance of above-average, a 33.3 percent chance of average, and a 26.7–33.3 percent chance of below-average precipitation. A shade darker green indicates a 40.0–50.0 percent chance of above-average, a 33.3 percent chance of average, and a 16.7–26.6 percent chance of below-average precipitation, and so on.
Equal Chances (EC) indicates areas where no forecast skill has been demonstrated or there is no clear climate signal; areas labeled EC suggest an equal likelihood of above-average, average, and below-average conditions, as a “default option” when forecast skill is poor.
For more information on CPC forecasts, visit:
For IRI forecasts, 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