Precipitation

The few storms during the 2011 water year (from October 1) generally have moved from southwest to northeast across the southwestern U.S. Virtually all of the winter storms have passed over the northwest corner of Arizona, while very few storms have moved through southern New Mexico or southeastern Arizona. This has left a precipitation gradient, with dry areas in the southeast receiving less than 50 percent of average precipitation and relatively wet areas to the northwest receiving 130 percent to more than 300 percent of average precipitation (Figures 2a–b). Most areas in between have received less than 70 percent of average. Southeastern San Juan County in northwestern New Mexico also received more than 300 percent of average precipitation. The pattern of the past 30 days has been very similar, with 150–300 percent of average precipitation along the lower Colorado River and the northwest corner of New Mexico, less than 5 percent of average across all of New Mexico except the northernmost counties, and 5– 50 percent of average precipitation in southeastern Arizona (Figures 2c–d). This is a typical pattern for a La Niña year, during which storms tend to remain well north of Arizona and New Mexico. The few storms that have come through the northwest corner of Arizona have tapped into subtropical moisture, resulting in very heavy rain or snow.