There have been a few sprinkles around the Valley of the Sun this week, but Phoenix Sky Harbor is still waiting for its first measurable rain of Monsoon 2020.

When looking at the number of years rain has fallen on a particular day during Monsoon in Phoenix from 1896 - 2019 (124 years), it is rather easy to see the peak is August 3rd (just under two weeks away), coming in with 26% of years recording measurable rain. So does this mean a dry monsoon is likely this year?

There is no real correlation between the first day of measurable rain during monsoon and the overall season rainfall total. But there is more to the story... Breaking the past 124 years of monsoon data into 31-year blocks, based on the first measurable rain during the monsoon, interesting results emerge (graphic below).

The highest average and median monsoon rainfall totals seem to occur when the first day of rain is between June 30th and July 7th. Interestingly, this period also contains the driest monsoon on record, coming in with just 0.35" of rain.

On the flip side, based on average and median rainfall, the driest seasons tend to be when rain the first rainfall occurs early in the season (June 15th - 29th) or later in the season (July 16th - August 14th).

So there is a slightly tilted chance this year will come in on the dry side; however, as we all know, monsoon storms can be very isolated, and just one or two good storms can quickly change the game!

Fingers crossed for rain!