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Forecasts
Published August 25, 2010

Precipitation Outlook

 (September 2010–February 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 monsoon season and early fall for all of Arizona and western New Mexico, with Arizona experiencing the greatest tilt in the odds toward drier conditions (Figure 11a). This outlook is influenced heavily by the La Niña event, and the CPC recently issued a La Niña Advisory, which means that La Niña conditions have been observed and are expected to continue (see page 19). La Niña conditions historically favor below-median precipitation from the September–November period in the Southwest. Seasonal outlooks for the winter also favor drier-than-average conditions in the Southwest, strongly reflecting the effect La Niña has on winter precipitation in the Southwest (Figures 11b–11d).

Photo of Long lead National precipitation
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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