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Forecasts
Published September 23, 2010

Precipitation Outlook

 (October 2010–March 2011)
Data Source(s): NOAA-Climate Prediction Center (CPC)

The NOAA–Climate Prediction Center (CPC) precipitation outlooks suggest drier-than-average conditions for the remainder of the fall and early winter in all of Arizona and western New Mexico (Figures 10a–d). This outlook is influenced heavily by the current moderate to strong La Niña event. During La Niña events since 1950, winters in the southwestern U.S. and particularly Arizona have been dry between 60 and 80 percent of the time. The outlooks indicate that nearly all of New Mexico and southern Arizona have greater than a 40 percent chance for experiencing precipitation totals that are similar to the driest 10 years in the 1971–2000 period.

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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