1) I always used 10w30 in my first car (1970 LeMans, over 30 years ago) year round. Back then it was the only light multi-grade commonly available. Temperatures got down (and still do) to -30C (-22F) regularly. Sold the car at over 100,000 miles motor was mint.
2) Last winter, my 2006 Sierra accidentally got caught out with 10w30 in the crankcase all winter (I did not put on the anticipated mileage that previous summer), same temperature extremes. It was fine. I did not like doing that (10w30 in the winter) but it was what it was.
Where you live 10w30 will never give you a cold flow issue.
Having said all this, personally I am a big 5w30 advocate (or lighter i.e. 5w20 if the manufacturer approves) for all year operation. I just have some 10w30 in my stash to use up. I plan to use 10w30 VR1 for my Chevelle if it is ever on sale, right now I use T5 10w30 in it but to the point of your post, I do not operate it below 40F generally.