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Forecasts
Published October 24, 2012

Precipitation Outlook

 (November 2012–April 2013)
Data Source(s): NOAA-Climate Prediction Center (CPC)

The seasonal precipitation outlooks issued by the NOAA-Climate Prediction Center (CPC) in November call for equal chances that precipitation during the three-month seasons spanning the November–April period will be above-, below-, or near average (Figures 9a–d). Equal chances mean that forecasts do not have any evidence in their decision support tools that allow them to alter the probabilities toward either above or below average—in other words, forecast skill is no better than flipping a coin. A major reason for equal chances is that the ultimate fate of ENSO is in doubt. A few months ago, the expectation was that an El Niño event would develop. However, recent indications suggest that ENSO may remain in neutral or, even if an El Niño does materialize, it will likely be weak and short-lived. Without a strong ENSO signal or any clear decadal trends in precipitation for the Southwest, there is little insight about this winter’s precipitation. Uncertainties aside, with widespread and intense drought across the Southwest, many resource managers are hoping for wet conditions.

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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