The monsoon that has been lighting up the rest of Arizona has a second, meaner edge, and this one sets up southeast of Phoenix. The National Weather Service in Tucson expects storms to fire across Pinal, Pima, and Santa Cruz counties through the afternoon and into the evening, and the setup this time favors the organized, severe kind rather than the weaker cells that have been fizzling farther west.
For anyone who has not driven through a desert storm like this, the danger is not really the rain. A monsoon cell builds fast, throws down everything it has in a few minutes, then falls apart. When it falls apart it kicks a blast of wind out ahead of itself, and that wind drags a wall of dust across the highway. Whatever rain does land hits ground baked hard as pavement and runs off into washes that were dry all afternoon. One storm, two ways to get killed: blind you first, then flood the dip you were about to cross.
The setup is there today. Dew points are up in the upper 50s across the three counties, instability is running 1000 to 2000 J/kg, and there is just enough shear to keep the storms from collapsing into a mush. The Storm Prediction Center has the area in a Slight Risk, level two of five. Translated for the road: two hazards, both fast, both arriving right around the evening drive.
Peak Driving Danger Window
Storms should get going in the early afternoon along that Pinal-to-Santa Cruz convergence, then track west through the evening. Bad timing, in other words, landing on the evening commute and the tail end of weekend travel…