This is not a clarification of my own outlook, which I haven't comitted to (yet), but a clarification of reporting about other outlooks. On the weekend of June 1-2 the Tucson paper published online a story headlined, 2024 Monsoon outlook: Hotter, drier summer in Tucson.
The story repeatedly refers to something it calls the National Weather Service 2024 Monsoon Outlook, which the story says was newly released last week. I'm not familiar with such a product, but stand ready to be educated. I'm guessing that most of the time the reporter is summarizing and interpreting Climate Prediction Center three-month outlooks for Jun-Jul-Aug and Jul-Aug-Sep. I'll comment more about this later.
The fourth paragraph of the Tucson story reads,
Last year was the 17th-driest monsoon across Arizona since 1895, according to the National Weather Service 2024 Monsoon Outlook. Tucson received only 4.73 inches of rain in 2023 or .96 inches less than average, National Weather Service records show.
There's that mysterious (to me) Outlook reference again. Last year's 4.73 inches was the 39th driest in Tucson since 1895 (NWS Tucson -> Monsoon -> Monsoon Stats -> scroll to "Haywood plot"), a far cry from 17th driest. My impression of last year's monsoon in Tucson is in line with how it was summarized by azcentral. After they reported how dry Sky Harbor airport had been during the 2023 monsoon, they wrote:
As a whole, the deviation from the norm for Tucson is not that negative. A typical season usually produces around 5.7 inches of rain for Tucson's airport, coming mainly in July and August. This was mirrored in 2023, as the prime months brought 2 and 2.39 inches, respectively, making up for a zero in the June column and a lackluster September.
It's important to remember that the Climate Prediction Center issues outlooks that provide probabilities for three categories: bottom 1/3, middle 1/3, and upper 1/3. Last year's Tucson monsoon coming in at 39th driest since 1895 puts it in the bottom 1/3 (i.e., 1895-2023 = 129 years, bottom 1/3 = 43 driest years). The current CPC Jun-Jul-Aug outlook tilts the odds just slightly toward the bottom 1/3 (33-40% chance), which leaves 60-66% chance for either middle one-third or upper one-third. The CPC outlook for Jul-Aug-Sep is a little more pessimistic, but still leaves a 50-60% chance for either middle one-third or upper one-third.
I agree with two quotes in the Tucson news story from Michael Crimmins: ... forecasting the monsoon is incredibly hard
and ... the summer impact of La Niña on the monsoon is actually quite weak.
My bet, or maybe it's just wishful thinking, is that above normal temperatures that are expected to persist over New Mexico will instead by July have shifted a bit toward north Texas. The circulation around the southwest side of the associated upper-air area of high pressure (what media have taken to calling a heat dome) would favor squall lines on several days sweeping across Tucson during the afternoon and early evening, effectively squeezing out available moisture. That's a pattern that has been lacking in recent years, but it's due.
