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Forecasts
Published July 25, 2012

Precipitation Outlook

 (August 2012–January 2013)
Data Source(s): NOAA-Climate Prediction Center (CPC)

The seasonal precipitation outlooks issued by the NOAA-Climate Prediction Center (CPC) in July call for slightly increased chances that precipitation during the August–October and September–November periods will be similar to the wettest 10 years in the 1981–2010 record for parts of southern Arizona and New Mexico (Figures 11a–b). These areas correspond to the region most heavily influenced by the monsoon. This forecast is influenced by the expectation that El Niño will continue to develop in coming months. Based on past El Niño events during these periods, there are increased chances for above-median precipitation from Southern California to New Mexico and as far north as Utah and Colorado because convection in the eastern Pacific Ocean instigates moisture surges into these regions. There are also increased odds that precipitation will be above average during the October–December and November–January periods (Figures 11c–d). This, too, relates to El Niño, which often alters atmospheric circulation patterns so that more storms soak the Southwest.

 
Seasonal Precipitation Forecasts for the U.S.
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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