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Forecasts
Published August 23, 2011

Precipitation Outlook

 (September 2011-February 2012)
Data Source(s): NOAA-Climate Prediction Center (CPC)

The seasonal temperature outlooks issued by the NOAAClimate Prediction Center (CPC) in August call for slightly increased chances for precipitation during September–November and October–December to be similar to the driest 10 years of the 1981–2010 period (Figures 11a–b). The greatest chances are in the southern portions of both states. These forecasts are based in part on current dry soil moisture conditions and trends for drier conditions during these periods. For November–January, the CPC calls for equal chances of above-, below-, or near-average conditions (Figure 11c) for most of the region. The southern tier of the region has slightly enhanced odds at drier-than-average conditions for the December–February period (Figure 11d). This forecast is influenced in part by the increasing likelihood that a La Niña event will develop this winter. La Niña events historically bring dry conditions to the Southwest.

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 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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