Home » February 2012 Southwest Climate Outlook » Precipitation Outlook
Forecasts
Published February 22, 2012

Precipitation Outlook

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

The seasonal precipitation outlooks issued by the NOAA-Climate Prediction Center (CPC) in February call for increased chances that precipitation will be similar to the driest 10 years of the 1981–2010 period for the March–May and April–June periods in all of Arizona and New Mexico (Figures 10a–b). Probabilities for below-average precipitation are highest in March–May. For this period, there is a 50 percent chance that precipitation will be between 0.2 and 0.4 inches below average in nearly all of both states. A primary driver for these forecasts is the La Niña event, which likely will persist into spring but appears to have peaked, according to the CPC. La Niña events historically bring dry conditions to the southern tier of the U.S., including Arizona and New Mexico, and wetter-than-average conditions to the Pacific Northwest. Outlooks for May–July and June–August call for equal chances for above-, below-, or near-average conditions in Arizona and most of New Mexico (Figures 10c–d).

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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