Paul's Note - Sept. 3, 2021

Anyone who has lived in Tucson for more than a few years knows about our monsoon season. Last year’s monsoon season was, well, a bit less than what we would expect. August is typically our wettest month at just a shade under 2.5 inches of rain. We only had 1.6 inches of rain the entire monsoon season in 2020, running from mid-July to September. 

This year, however, has provided us with a historic amount of  rainfall. We got 3.8 inches in August this year, after a July where we had over 8 inches. 

We love the rain, but it has caused problems. My staff fielded calls about debris that had washed into arroyos, damage to streets and even houses that flooded. 

As a result of climate change, what used to be a predictable monsoon season is likely not going to be anymore. Last year, we had a minimal monsoon (and only 4.2 inches all year, a number we blew past in mid-summer). This year, it’s storm after storm. Rising ocean temperatures have changed the way storms are formed and move in our area, while the rising air temperatures and the urban heat island effect have made the storms we get more intense. 

We have a rain gauge here at the office and participate in a website called Rainlog.org. Below is their report about Arizona’s August rains: 

This active 2021 monsoon continued across much of southern Arizona, but slowed a bit across the northern half of the state. Deep monsoon moisture remained parked in the low deserts of southern Arizona all month long, but some passing low pressure systems to the north periodically shoved the ‘Four Corner’s High’ out of position leading to a couple of extended breaks in widespread thunderstorm activity across the state. 
 
The most active period of widespread precipitation occurred mid-month as the upper level ridge pushed north across the western U.S., leaving Arizona in a broad area of easterly flow. This allowed an upper level low to move from east to west across the region (similar to the widespread precipitation event in July). This upper level low in conjunction with deep moisture supported widespread heavy precipitation across Arizona between August 10th and the 15th, when RainLoggers from Douglas to Prescott reported precipitation totals ranging from 2 to 4 inches. Numerous RainLoggers on the east side of Tucson reported some of the highest totals of this period, with observations ranging from 5 to 7 inches. 
 
Monsoon activity slowed again for the remainder of the month until moisture from Hurricane Nora pushed back into the state at the end of August. RainLoggers from Pine to Oracle saw most of the initial activity, with daily precipitation totals ranging from 2 to 3.5 inches on August 31st. 
 
Overall, most of central and southern Arizona observed above-average precipitation while the northern half of the state saw below-average totals for August. Changes in short-term drought conditions on the U.S. Drought Monitor also followed this pattern with most of the improvements occurring across southern and central parts of the state. Prior to the monsoon, much of the state was in “exceptional” drought, but heavy monsoonal precipitation has dramatically improved drought conditions, first to “extreme”, then “severe”, and as of August 31, the majority of the state is now in “moderate” drought.  See the U.S. Drought Monitor Map at https://droughtmonitor.unl.edu/CurrentMap/StateDroughtMonitor.aspx?AZ. 
 
Monsoon precipitation typically winds down through September, but the 1-month precipitation outlook issued by the NOAA Climate Prediction Center on August 31st indicated an increased chance of above-average precipitation through the end of September for much of Arizona and New Mexico.