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Published March 27, 2013
Precipitation Outlook(April–September 2013)
Data Source(s): NOAA-Climate Prediction Center (CPC)
The seasonal precipitation outlooks issued by the NOAA-Climate Prediction Center (CPC) in March call for increased chances that precipitation during the April–June period will be below average across many parts of the Southwest except in southern regions (Figure 10a). The April–June period, however, is historically dry. Most of Arizona and southwestern New Mexico, for example, receive less than 12 percent of their annual precipitation during these months. As a result, below-average precipitation during these months likely will not exacerbate drought conditions. Precipitation anomalies are only expected to be between 0.1 and 0.4 inches if below-average rain and snow occurs. Seasonal forecasts that overlap the monsoon show equal chances for above-, below-, or near-average precipitation for most of Arizona and part of southwest New Mexico (Figures 10b–d). The CPC notes, however, that dynamical models show a continuation of the tendency for below-median precipitation in parts of the Southwest monsoon region through summer.
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 1981–2010 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
- 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