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Forecasts
Published March 24, 2011

Precipitation Outlook

 (April 2011–September 2011)
Data Source(s): NOAA-Climate Prediction Center (CPC)

The NOAA–Climate Prediction Center (CPC) precipitation outlooks suggest drier-than-average conditions for the spring months across most of Arizona and New Mexico (Figure 10a). In spite of the forecasted weakening of La Niña in the spring, very low soil moisture conditions across much of the Southwest may decrease local moisture sources through evaporation and increase the chances for the continuation of below-median precipitation into spring. As we move into the monsoon season, CPC precipitation outlooks call for equal chances for above-, below-, or near-average conditions (Figures 10b–d), primarily because the monsoon season is difficult to forecast this early in the spring. As the monsoon season approaches, more accurate forecasts will be available.

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 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.

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