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Forecasts
Published July 25, 2011

Precipitation Outlook

 (August 2011-January 2012)
Data Source(s): NOAA-Climate Prediction Center (CPC)

Analysis tools are providing conflicting signals for monsoon precipitation, according to the NOAA-Climate Prediction Center (CPC). Several forecast model ensembles suggest the possibility of a weak monsoon for the Southwest and southern Rocky Mountains. On the other hand, a springtime precipitation pattern similar to what was observed earlier this year—dry conditions in the southern Rockies and wet conditions in the northern Rockies and Pacific Northwest—has been associated with an active monsoon season. However, the historical accuracy of these models has not fared well. As a result, CPC forecasts an equal likelihood of near-average, above-average, and below-average precipitation in Arizona and New Mexico during the August–October period (Figure 11a). For the September–November, October–December, and November–January lead times, the forecasts also call for equal chances of above-, below-, or near-average conditions in most of Arizona, with slightly increased chances for below-average precipitation for the southern portion of New Mexico (Figures 11b–d).

Photo of Long lead National precipitation
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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