Monsoon thunderstorms are very isolated. During the monsoon months of June, July, August and September, we receive an average of 2.65 inches of rain. That’s nearly one third of our yearly rainfall total.
Rain with the summer monsoon comes so fast and so quick that our dry desert soil can’t take all of it in. The result is flash flooding. Streets, washes and riverbeds all fill up with water without any kind of warning. Our wettest monsoon occurred in 1984, when we picked up 9.38 inches of rain. The driest monsoon was in 1924, when we saw only .35 inches of rainfall.
Last year’s monsoon was dismal. The official start date was July 19 and it lasted through Sept. 11, 2007. The official total comes from Phoenix Sky Harbor International Airport, where we picked up only .74 inches of rain, making our total well under the average.
However, because the thunderstorms are so isolated, other Valley cities such as Cave Creek and Carefree picked up well above our yearly average, which is good for Arizona’s water supply.
Something that is rare during the monsoon – but can happen occasionally – is hail. Once the water droplets get into the clouds, they begin to freeze and collect on each other.
When they begin sticking, giant pieces of ice form. As these pieces of ice become heavier, they fall through the thunderstorm. As they fall, the air temperature warms causing the ice to melt. If the ice melts completely, it comes down as rain. If it doesn’t melt, it comes down as hail.
