Home » June 2011 Southwest Climate Outlook » Precipitation Outlook
Forecasts
Published June 20, 2011

Precipitation Outlook

 (July 2011-December 2011)
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, an active monsoon season has occurred in the past when spring precipitation patterns have been similar to conditions observed earlier this spring—dry in the southern Rockies and wet in the northern Rockies and Pacific Northwest. At this time, observations from western Mexico where the monsoon rains begin suggest a delayed onset and are consistent with the forecast models, which call for below median-precipitation for the July–September period. However, the historical accuracy of these models has not faired 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 monsoon season (Figure 10a). For the two-, three-, and four-month lead times, the forecasts also call for equal chances of above-, below-, or near-average conditions, with slightly increased in chances for below-average precipitation for the southern portion of the region in early winter (Figures 10b–d).

Map of United states depicting the National Precipitation forecast
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.

Related Links: