Autumn in the Southwest

Heading to California? Arizona? Nevada? Even Utah, Colorado, or New Mexico? We’ve got the perfect article for you.

Tuesday, September 24, 2024 at 04:11 AM ET

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This early fall pattern in September shows the Southwest heat low over western Arizona and a very strong North Pacific High dominating weather along the coast. (Tim Vasquez/AWIPS plot)

Key Takeaways:

Autumn in the Southwest transitions from summer's monsoonal patterns to dynamic weather driven by stronger upper-level winds and frontal systems, replacing the Southwest heat low with the dominant Great Basin High.
This shift introduces hazards such as powerful Santa Ana winds (causing turbulence and wildfire risk), intense Rocky Mountain windstorms with clear-air turbulence, and persistent valley fogs (like "tule fog") that can significantly reduce visibility.
Pilots must also account for tropical storm remnants, which frequently impact the region with heavy precipitation and low ceilings, particularly in September.
The Pacific storm track intensifies and moves south into California by late autumn, bringing widespread precipitation and jet stream activity, especially amplified during El Niño years.

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Complacency can easily creep in during the summer. It seems like all we have to worry about is the air mass and orographic thunderstorms that pop up late in the day. Once autumn arrives, we end up with a new set of ingredients on our plate. The weather becomes more dynamic, upper-level winds increase, we start dealing with frontal systems, and the tropics explode with hurricanes. How can we make sense of all these changes?

Here, our attention is on the Southwest, including not only the Rockies but the Great Basin and California. What are good strategies for planning your flights in September, October, and November? What can you expect?