(data between June 16-July 15, 2013 )
Data Source(s): Western Regional Climate Center
The monsoon kicked off around July 1 in southeast Arizona, and has delivered copious rains there, to parts of the Mogollon Rim region, and to the west-central mountains of New Mexico (Figure 9a). Rain has been scant, however, in western and central Arizona, around Phoenix, and in southwest New Mexico. The monsoon high has been generally located in a good position to help steer moisture in the middle atmosphere from the east and push storms off the mountains into the lower elevations. Also, a few surges of near-surface moisture from the Gulf of California have arrived. Many locations in southeast Arizona have experienced above-average rain, including the Douglass airport where about 8 inches have fallen through July 17 (the historical average is 1.58 inches; Figures 9b–c). At the Tucson International Airport, 1.65 inches have fallen through July 17, which is 0.69 inches above average for this time of year. Phoenix International Airport, however, has not received any substantial precipitation this summer. For the past two weeks, the amount of water vapor in the air, as measured by the dew point temperature, generally has been above average. The same period has been marked by frequent atmospheric instability, near-surface moisture, and sufficiently strong steering flows—three ingredients needed for widespread rainfall—but not always at the same time or place. These conditions have developed more synchronically at higher elevations and close to the U.S.-Mexico border where large mesoscale convective systems have spilled over into Arizona.
The monsoon, as always, has been spotty, with higher elevations often experiencing more rain than the valleys—topography often helps initiate rainfall by forcing air upwards, where it cools, condenses, and is squeezed like a sponge. For example, a storm on July 13 produced more than 2 inches of rainfall on Mount Lemmon, north of Tucson, while surrounding valleys were drier.
Where it has fallen, the monsoon precipitation has helped improve short-term drought conditions. Range and croplands in the Southwest have greened up in the last two weeks, and the rain has helped quell fire risk (see Recent Fire Summary).
The continuous color maps (figures at right) 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.
Average refers to the arithmetic mean of annual data from 1971–2000. Percent of average precipitation is calculated by taking the ratio of current to average precipitation and multiplying by 100. Departure from average precipitation is calculated by subtracting the average from the current precipitation.