A brief but powerful afternoon storm that dumped rain and hail on Nogales last Thursday aptly punctuated the end of an exceptionally wet monsoon season in the local area.
The season runs from June 15 to Sept. 30 in Arizona, and during that period in 2021, rain gauges around Santa Cruz County collected an average of more than 14 inches of precipitation. That was well above the county’s norm of 11 inches, and two-and-a-half times the 5.6-inch countywide average of the underperforming 2020 monsoon.
This was the wettest monsoon in Santa Cruz County in the past decade, and John Hays, the county’s floodplain coordinator, said it ranked as one of the two or three rainiest seasons in the 21 years he’s been on the job.
The wettest spot in Santa Cruz County this monsoon season was Peña Blanca Lake, where a gauge operated by the Arizona Game and Fish Department recorded 23.7 inches of precipitation. A county gauge at Patagonia Lake measured 15.6 inches, and another in the town of Patagonia was right behind at 15.5 inches.
Nogales also got its fair share of precipitation, with more than 15 inches recorded at two gauges on the west side of the city, and just under 15 inches on the east side.
Peck Canyon in Rico Rico also came in at just under 15 inches, though a gauge up the road at the Santa Cruz River in Tubac counted only 8.7 inches – the lowest level of any of the 13 gauges for which data was available in the county.
And while the rains offered welcome relief after an unusually hot and dry 2020, and improved most of the county’s drought status from extreme to severe and then to moderate, Hays said he would still prefer to see more substantial rainfall in the winter.
“The difference between winter and the monsoons is that the winter rains tend to come with lesser intensity of rainfall, which means you get the water over a longer period of time, which means more water soaks into the ground than runs off,” he said.
“Since our potable water supply is dependent on the groundwater aquifer, we want as much of that water to soak into the ground as we can get,” he added.
High-intensity monsoon rains can also be dangerous, and the 2021 season brought flash flooding and even death to the local area. A 13-year-old boy died after being overcome by floodwaters near a waterfall in Rio Rico on July 29, and two women, ages 24 and 39, were killed in flash flooding in Nogales, Sonora on July 27 and Aug. 30.
Santa Cruz County’s total annul rainfall is usually around 17 inches, with six inches expected in the winter months. Speaking Monday morning, Hays said forecasts for the upcoming winter season haven’t offered any definitive predictions, though he noted that there was potential for rain in the next day or two in the area.
The National Weather Service in Tucson was forecasting a 30-percent chance of thunderstorms in and around Nogales starting Monday afternoon, increasing to 40 percent overnight. There was another 30-percent chance of storms during the day on Tuesday, before the storm system is expected to give way to mostly clear conditions on Tuesday night and sunny weather on Wednesday.
The wetter-than-normal weather this summer helped keep the temperatures under control once the rains arrived in earnest in July.
The average daily high at the airport was 90.2 in July, 90.6 in August and 89.5 in September – all below normal. The typical daily highs at the airport during those months are 94.2, 92.4 and 90.3, respectively.
In addition, there were only 13 days during the 110-day monsoon season on which the temperature reached 100 degrees or more at the airport, and none after July 10.
In 2020, the mercury hit or topped 100 degrees at the airport 46 times during monsoon season.