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 marks a shift from summer's static weather to dynamic conditions, driven by decreasing solar radiation, stronger upper-level winds, and the fading of the summer heat low.
The region becomes dominated by the Great Basin High, which often brings clear, cold weather, but also localized inversion fogs (like "tule fog" in San Joaquin Valley) and potential Santa Ana wind events in California, increasing wildfire risks.
Despite natural shielding, the Southwest can be impacted by remnants of tropical storms and hurricanes from Mexico, particularly in September, causing heavy precipitation, low ceilings, and restricted visibility.
Late autumn establishes the Pacific storm track, bringing frontal systems, widespread precipitation, and strong jet stream winds to the West Coast, signifying the region's transition into the cold season.

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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?