It was 45 here this morning too.
I don't wear a jacket until it gets colder than that, or I get too hot.
I'm a big fan of arm warmers and leg warmers because you can take them off if the day gets warmer as you're riding. I wear leg warmers when the temps drop below 55, or if it's real windy.
I try to wear layers of tops, rather than a jacket. Today I wore a short sleeve merino wool T-shirt under my bike jersey with arm warmers and a wind-proof vest. It warmed up as we rode, so I took off the arm warmers and vest. (I always carry a little fanny pack or stuff things into my jersey pockets.)
Hope this helps. Your climate sounds similar to mine.
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