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Forecasts
Published May 26, 2011

Precipitation Outlook

 (June 2011–November 2011)
Data Source(s): Data Source: NOAA-Climate Prediction Center (CPC)

The NOAA–Climate Prediction Center (CPC) forecasts an equal likelihood of near-average, above-average, and below-average precipitation in the Southwest during the summer and into the fall (Figures 11a–d). This equal chances forecast is based in part on the difficulty in projecting the monsoon, which typically begins in early July and ends in late September. As the monsoon approaches, more accurate forecasts of the monsoon season will become available. Research on the monsoon indicates that a dry winter generally is followed by a wet monsoon. However, this pattern has not always held true.

Precipitation Outlook
Notes:

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.

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