Storm Postmortem: Explaining the weekend donut hole over Tucson

Courtesy: NWS Tucson
Courtesy: NWS Tucson

For much of southern Arizona, the predicted rainfall panned out over the weekend. Tucson? Not so much, as the Old Pueblo was one of VERY few places to stay mostly dry. So what happened? Let’s rewind to Friday morning.


One of the tools I rely on heavily during the Monsoon is the upper air data from weather balloons (skew-T for the weather geeks reading). Above is the upper air data from Friday morning in Tucson. I know, a ton of lines, numbers, super confusing, but stay with me here. See the space between the dark red dashed line (lifted air parcel) and solid red line (temperature profile)? That’s an indication the atmosphere is unstable and can sustain storms.  While on-air Friday morning, we had storms already firing up.


Here’s the upper air data from Friday evening. Look how close together the dashed dark red line & solid red line are. Morning storms and subsequent cloud cover completely sapped the atmosphere of any energy for further development. Indeed my 60% call for Friday goes down as a “bust”.


Now onto Saturday. Here’s the morning upper air data, again showing instability in the atmosphere. It also indicates a familiar problem we have with storm development. I highlighted the wind barbs at the 500mb line and the 200mb line. At 18,000 feet (steering level for storms), winds were out of the southwest at roughly 15 mph. Meanwhile around 30,000 feet, winds were also from the southwest, at a stronger 40 mph.

This wind profile is synonymous with “anvil shading”, which tends to hijack Tucson’s storm chances frequently. The video above demonstrates.

Just goes to show how finicky the Monsoon can be. You can have all the tropical moisture in the world, but if there’s no energy & poor winds, someone’s going to get skunked of much needed rainfall. That someone was Metro Tucson this past weekend.


2 thoughts on “Storm Postmortem: Explaining the weekend donut hole over Tucson

  1. Thanks for the geeky explanation Jeff.

    I have only lived in Tucson for 3 years(moved from Chicago) but have noted that the computer models seem to struggle with tropical systems. Is that due to relative lack of upper air information(etc) for oceanic systems ?

    1. Absolutely! Compared to the Atlantic, which is dotted with buoys, the Pacific is a data dead zone. Certainly more buoys would help in situations like this. Thanks for reading!

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