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Forecasts
Published January 25, 2011

Precipitation Outlook

 (February–July 2011)
Data Source(s): NOAA-Climate Prediction Center (CPC)

The NOAA–Climate Prediction Center (CPC) precipitation outlooks suggest drier-than-average conditions into the spring for all of Arizona and New Mexico (Figures 10a–c). The highest chances for decreased precipitation will be in the February–April period, which in part reflects the expectation that the La Niña event will persist through March–May. Chances for below-average precipitation during the March–May period also are elevated, ranging between 40 and 50 percent for all of Arizona (Figure 10b). La Niña events typically are associated with below-average precipitation in the Southwest. Since 1950, winters in the southwestern U.S. and particularly Arizona have been dry between 60 and 80 percent of the time. Chances for below-average precipitation are slightly elevated during the April–June period (Figure 10c), and the late spring and early monsoon outlook calls for equal chances of above-, below-, or near-average conditions (Figure 10d).

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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