The University of Arizona

Precipitation | CLIMAS

 SW Climate Outlook


Data through September 18, 2013. Data source: High Plains Regional Climate Center.

Winter precipitation, which brought more rain and snow to the higher elevations of central Arizona and northern New Mexico (albeit below average in New Mexico), and the monsoon, which is historically heterogeneous in space, hascontributed to the high geographic variability during the 2013 water year. Higher elevations in Arizona and parts of the lower Colorado River Valley have been wetter than average since October 1, while high elevations in northwestern New Mexico have been dry (Figures 2a–b). The wet conditions along the western border of Arizona are due in part to moisture from several tropical storms during the monsoon that moved north along the Baja coast. 

Many locations in both states received a large fraction of their water year precipitation in the past 30 days, as large plumes of subtropical moisture moved north from Mexico and lingered over the Southwest before moving into Colorado (Figure 2c–d). Despite high rainfall in the last 30 days in New Mexico that was between 150 and 800 percent of average, the precipitation deficit that accumulated over the water year was large enough that it continues in many regions. Nonetheless, rain in the last 30 days, combined with earlier summer rains, helped improve drought conditions across Arizona and the Southwest (see Arizona and New Mexico Drought Statuses). However, drought is still present in most of the Southwest, and winter precipitation will go a long way to sustaining these improvements or worsening conditions. Based on long-term trends, there is some evidence that parts of the Southwest will experience a fourth consecutive winter with below-average precipitation (see Precipitation Outlook).


The water year begins on October 1 and ends on September 30 of the following year. As of October 1, 2012, we are in the 2013 water year. The water year is a more hydrologically sound measure of climate and hydrological activity than is the standard calendar year.

Average refers to the arithmetic mean of annual data from 1981–2010. Percent of average precipitation is calculated by taking the ratio of current to average precipitation and multiplying by 100.

The continuous color maps (Figures 2a, 2c) are derived by taking measurements at individual meteorological stations and mathematically interpolating (estimating) values between known data points. Interpolation procedures can cause aberrant values in data-sparse regions.

The dots in Figures 2b and 2d show data values for individual meteorological stations.