Sky Harbor International Airport spokeswoman Julie Rodriguez says there are 20-minute arrival delays and a few departure delays shorter than that Tuesday morning.
Rodriguez said the delays result from the need for more spacing between aircraft as pilots use instrument procedures instead of visual ones.
She says the impact isn't significant so far.
The National Weather Service said locally dense fog will persist across parts of the metro area through late Tuesday morning.
The weather service said visibility in some areas is dropping to a quarter-mile or less, and it says the places with the most dense fog is the Salt River's bed. Sky Harbor is located next to the river bed.
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