A San Francisco-bound United flight diverted to Palm Springs yesterday after a threat of low visibility became evident in the Bay Area. The service had originated in Tuscon, Arizona, and was being operated under the United Express brand by a SkyWest Airlines Bombardier CRJ200ER. Such disruption is not uncommon in San Francisco, a city known for its fog.

The flight in question

United Airlines flight UA4682 is a regularly scheduled service that originates at Tucson International Airport (TUS) in Arizona. Operated under the carrier's regional brand, United Express, it has a scheduled departure time of 08:00. Its destination is California's San Francisco International Airport (SFO), where it touches down at 09:31 local time.

This gives a duration of just over two and a half hours, accounting for the time difference. While United serves several destinations from Tucson under both its mainline and Express brands, San Francisco is solely the domain of the latter. United Express is the only brand to offer a direct link between the two cities, with the flights operated by Skywest Airlines.

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United Express Bombardier CRJ
SkyWest Airlines operates flights for several US regional brands. Photo: Tomás Del Coro via Flickr

Diverted to Palm Springs

Data from RadarBox.com shows that yesterday's iteration of flight UA4682 was operated by a Bombardier CRJ200ER, registered as N967SW. According to ch-aviation.com, this 50-seat regional jet is 18 years old, having been delivered to SkyWest Airlines in November 2003. It took off from Tucson as planned yesterday morning, albeit slightly late at 08:22.

However, en route to San Francisco, the flight had to divert to Palm Springs International Airport (PSP), also in California. While the reason for this was unclear at first, it later emerged on social media that low visibility at the flight's planned destination could be the cause. After circling for a while outside Palm Springs, the flight landed at 09:20 local time.

After just over two hours on the ground, the flight was able to get back underway once again. It left PSP at 11:31, and touched down in San Francisco just over an hour later at 12:42. All in all, this represented a total delay on arrival of three hours and 11 minutes. A United spokesperson later confirmed to Simple Flying that weather caused the diversion.

San Francisco Fog
Foggy conditions often lead to low visibility in San Francisco. Photo: runner310 via Wikimedia Commons

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Not the only disrupted United flight

It appears that flight UA4682 was not the only United service to experience disruption yesterday. Indeed, a mainline flight from San Diego also arrived late in the Bay Area, with United confirming on Twitter that fog was the reason for its delay. Operated by a Boeing 737-900ER, flight UA676 touched down just over an hour late, at 13:13 (vs 12:04).

San Francisco's prevailing meteorological conditions mean that fog is a frequent phenomenon in the Bay Area. This is likely a factor in SFO's unfortunate title of being California's most-delayed airport. SFGate adds that it ranks 10th in the US as a whole, with 19% of flights delayed or canceled (2019-2021). With regards to yesterday's low visibility, CBS reports that a Dense Fog Advisory was in place for parts of the Bay Area until 11:00.

What do you make of this incident? Have you ever been on a flight that has diverted due to fog? Let us know your thoughts and experiences in the comments.