Home » April 2011 Southwest Climate Outlook » Precipitation Outlook
Forecasts
Published April 27, 2011

Precipitation Outlook

 (May 2011–October 2011)
Data Source(s): NOAA-Climate Prediction Center (CPC)

The NOAA–Climate Prediction Center (CPC) forecasts equal likelihood of near-average, above-average, and below-average precipitation in the Southwest during through October
(Figures 10a–d). This equal chances forecast is based in part on the difficulty in projecting the monsoon, which typically begins around July 1 and ends in late September. As the monsoon approaches, more accurate forecasts will be available. In the mean time, there is some indication that the spring and summer will continue to be warm and dry:  the very low soil moisture conditions that extend across much of the Southwest  may reduce the amount of water vapor returned to the atmosphere by evaporation, limiting storm formation. The current  soil conditions result from the La Niña-influenced dry winter.

Precipitation Outlook
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.

Related Links: