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Forecasts
Published June 27, 2012

Precipitation Outlook

 (July–December 2012)
Data Source(s): NOAA-Climate Prediction Center (CPC)

The seasonal precipitation outlooks issued by the NOAA-Climate Prediction Center (CPC) in June call for slightly increased chances that precipitation during the monsoon will be similar to the wettest 10 years in the 1981–2010 record for parts of southern Arizona and New Mexico (Figures 11a). These areas correspond to the region most heavily influenced by the monsoon. This forecast is based on the expectation that the monsoon will arrive early and deliver above-average rainfall totals in July, even though there is no indication of the monsoon’s strength in August or September. Forecasters at the CPC caution that the chances for a wetter-than-average summer are only slightly better than average or below-average odds.

For the seasonal outlooks spanning August–November, the CPC forecasts  equal chances that precipitation will be above, below, or near average (Figures 11b–c). The expectation that El Niño will develop in late summer or fall is causing the October–December outlook to favor wetter-than-average conditions because El Niño  events historically deliver copious rains to the Southwest during the winter (Figure 11d).
 

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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