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Forecasts
Published January 23, 2013

Precipitation Outlook

 (February–July 2013)
Data Source(s): NOAA-Climate Prediction Center (CPC)

The seasonal precipitation outlooks issued by the NOAA-Climate Prediction Center (CPC) in January call for increased chances that precipitation during the February–June period will be similar to the driest 10 years in the 1981–2010 period across most of the Southwest (Figures 10a–d). The highest probabilities for below average precipitation occur in the February–April period. If below-average precipitation occurs in this period, there is a 50-percent chance that deficits will be between 0.2 and 0.4 inches. The historical tendency for the West to receive below-average precipitation when ENSO neutral conditions occur during a negative Pacific Decadal Oscillation (PDO)—the current state—contributes to these forecasts.

Below-average rain and snow coupled with above-average temperatures has many implications for the coming spring and summer, including dry soil moisture and vegetation, continuing moderate to exceptional drought, and low water supplies.
 

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 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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