Other mistake: Over a car radio, KHJ's Robert W. Morgan is heard giving the weather forecast. The predicted high is "95 downtown, 105 in the valley." The scene takes place in the middle of winter, February 9, 1969.
Steven Lee
19th Apr 2020
Once Upon a Time in Hollywood (2019)
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Suggested correction: The daytime temperatures can reach that high in the winter.
The highest recorded temp for Feb 9 for Downtown LA is 89 set in 2016, and the highest February temperature ever there was 95 on Feb 20, 1995. "The valley" is too ambiguous to identify where it means. So while they "can", they don't, and any movie showing record-setting temps during winter, even if theoretically possible, would be considered wrong.