Home » March 2012 Southwest Climate Outlook » Precipitation Outlook
Forecasts
Published March 21, 2012

Precipitation Outlook

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

The seasonal precipitation outlooks issued by the NOAA-Climate Prediction Center (CPC) in March call for equal chances that precipitation will be above, below, or near average in most of Arizona and New Mexico (Figures 10a–b). While La Niña may give way to ENSO-neutral conditions in the tropical Pacific Ocean, enhanced probabilities for below-median precipitation continue in the April–June period in most of the Upper Colorado River Basin and parts of northern Arizona. This forecast is based in part on the delay response of the atmosphere to waning La Niña conditions and below-average soil moistures, which limit evaporation that would otherwise enhance precipitation.

For the summer months, forecasts have been less accurate during the monsoon season. Consequently, the CPC has no basis to favor wetter- or drier-than-average conditions and gives an equal chances outlook for the May–July, June–August and July–September periods.

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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