Officially, Monsoon 2022 started on June 15th and will end on September 30th, but before 2008, the dew point rule was used. The rule was that the monsoon started in the Valley of the Sun if the daily average dew point in Phoenix was 55º+ for three days in a row.

Some people (myself included) still like to track the dew point, and it is was great excitement to say that today (June 27th) will likely be the third day in a row with a daily average dew point of 55º+ at Phoenix Sky Harbor (57º on June 25th, 57º on June 26th, and estimated to be around 61º on June 27th). This means the monsoon, using the dew point rule, started on Saturday, June 25!

This ties as the 5th earliest start to the monsoon using the dew point rule.

Top five earliest starts:
1) June 17, 2000
2) June 19, 1958
3) June 21, 2001
4) June 23, 1954
5) June 25, 1984, 1999, 2022

Monsoon 2022 officially started on June 15th and since then (through June 25th), Phoenix Sky Harbor has measured 0.14" of rain. This makes it the 10th wettest start to monsoon since records began in 1896. Average rain during this time is just 0.01".

Also of note, over the past 127 years (since 1896) measurable rain has only been recorded in 21 years during the June 15th through June 25th time period.

List of wettest monsoon starts (June 15th-25th) from 1896 through 2022:
1972: 1.64"
1965: 0.91"
1899: 0.61"
1967: 0.44"
2000: 0.30"
1925: 0.21"
1933: 0.21"
1984: 0.18"
2021: 0.17"
1930: 0.16"
1949: 0.14"
2022: 0.14"
1950: 0.10"
1918: 0.08"
1958: 0.05"
1934: 0.03"
1988: 0.02"
1898: 0.01"
1966: 0.01"
1986: 0.01"
2001: 0.01"
All other years: 0.00"

Have you received rain yet this monsoon? If you have, congrats, but if you have not don't think this monsoon is a bust just yet!

Looking at the number of years Phoenix has seen rain on a given day throughout the year from 1896 through 2021, Phoenix is currently in the "pit of dryness". On average, only two to three years out of 126 see rain on any given day in June. That's not a lot, and shows the June rain this year is certainly rare.

On average, rain chances increase in early July and continue to rise until the first part of August, peaking on Aug 3rd.

Bottom line, this has been a unique start to monsoon 2022 and one we should be thankful for as it has given some beneficial rain to the parched landscape!

If you lived in the Valley of the Sun before 2008, you likely heard a lot about dew point during the monsoon! The reason for the dew point buzz: the dew point rule! Before 2008, the season was defined to have started after Phoenix had a daily dew point average of 55ºF or higher for three consecutive days. After 2008, fixed start and end dates were determined (June 15th - September 30th).

Even though the dew point rule is not the "official" way to determine the start of the monsoon, it is still fun to track! With that said, Monsoon 2021 started using the "unofficial" dew point rule on June 30th. The daily average dew point was 56º on June 30th, 57º on July 1st, and projected to be in the low 60s on July 2nd! Last year it didn't start until July 22nd.

Using this old dew point system, the average start date for Phoenix was July 7th, but it started as early as June 16th in 1925, and it began as late as July 25th in 1987.

Believe it or not, we are now past the halfway point when it comes to Monsoon 2020. So far this season (June 15th - August 12th), Phoenix Sky Harbor has measured a meager 0.10" of rain. This year now ranks as the second driest monsoon during this period, with the record driest going to 1995, when no rain fell until August 14th!

With the first half of the season being so dry, could we see a wet end to the season? Let's go to the data!

Back in 1995, at this same time, we had no rain; however, from August 13th - September 30th, an additional 7 days of rain was recorded with the monsoon total ending up at 4.58", which is well above the average of 2.71". So just because we start dry, we don't have to end dry!

Now, before you get too excited, let's look at the averages from the top 20 driest monsoons (June 15th - August 12th). On average, there are six days of rain between August 13th and September 30th, resulting in an additional 1.56" of rain. Using this average, it would leave Monsoon 2020 in Phoenix at 1.66", which is over an inch below the average.

Looking at the worst possible situation, no rain has fallen during the last half of monsoon in 1973 and 1945, which would leave Phoenix as 0.10". This would undoubtedly break the record for the driest monsoon on record.

On the flip side, in 2014, Phoenix received 5.84" of rain in the last half of monsoon, with 3.3" falling in just one day as moisture from a tropical system moved into the region.

So while odds are certainly leaning toward a dry end to Monsoon 2020, don't let your guard down thinking there will be no more storms in the Valley of the Sun. There are some indications that tropical activity in the East Pacific could increase later this month into September, which could help to bring plenty of moisture to the state. After all, it really only takes one good storm to get us right back to average or even above average.

Keep thinking rain!

Since 2008, the monsoon has had fixed start and end dates of June 15th to September 30th. Before these dates were established, the monsoon was defined to have started in Phoenix when the daily average dew point was 55º or higher for three consecutive days.

Over the past three days (July 22nd-24th), Phoenix has recorded a daily average dew point of 55º or higher, so Monsoon 2020 started using the dew point method on July 22nd! The earliest start date was on June 16, 1925 and the latest occurred on July 25, 1987. On average, the start is around July 7th.

Even though this rule is not the "official" way to determine the start of the season, I still like to track it!

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!