Temperature

Temperatures since the water year began on October 1 have averaged between 65 and 80 degrees Fahrenheit in the southwest deserts and along the Arizona-California border, 50 to 60 degrees F across the Colorado Plateau in Arizona, and 45–60 degrees F across most of New Mexico (Figure 1a). This temperature pattern is typical of the early fall season where the transition from summer to fall temperatures occurs much more slowly in the deserts than in the higher elevations. Nighttime temperatures in the high elevations have already dipped below freezing, while the deserts have still had high temperatures in the low 100s and upper 90s. Since October 1, average temperatures in Southern Arizona and most of New Mexico have been 0 to 2 degrees F warmer than average, while the northern half of Arizona and central New Mexico have been 2 to 4 degrees F warmer than average so far this year (Figure 1b).  Only eastern New Mexico is starting the water year with cooler-than-average temperatures.  In the last month, temperatures have similarly been above average in nearly all the Southwest (Figures 1c–d). The map of the past 30 days shows the water year is beginning with the same warm pattern as the last water year ended.

Looking ahead, warmer-than-average conditions are forecast to continue through winter and into spring for the Southwest (see page 17). If warmer-than-average conditions occur, they will have a significant impact on the western snowpack by causing more rain to fall instead of snow at the elevations largely below 8,500 feet above sea level. This would, in turn, reduce the spring runoff.