This painting is now underway.
There is a reason why plein air painting has more adherents in the south western United States than elsewhere. In a word climate. Here is Eastern Canada we have two months of summer and the rest of the year, which includes micro temperatures some would not would not credit.
Full time painters are cagey about the use of photographs. I am not certain why having been raised in the "Coke bottle lens, b&w era of photography. They are a great visual aid especially at the pit of the year, and sometimes a chance shot, like that above, left, is almost ready for interpretation as a painting. I always try it first as a small 8x10" canvas before committing to anything of larger size.
There is no essential merit in plain air work over studio painting, except that the setting is better in terms of sunshine and fresh air and there is a much greater chance of having a conversation with someone interesting. On the other hand, California does lack those crisp, cold, beautifully overstated clear days of mid winter, which can't ordinarily be recorded on the spot. If you are a painter, take pictures, take plenty of them: work for the night is coming. In my experience three in one hundred will have some merit as the subject of a December painting.