Temperature here in Paris has dropped quite a bit since I last wrote here. This week, its hovering between freezing point and +3-4C during the daytime and you don't get to see the sun too much. So over the last few weeks I've had some quick experience in jogging in the cold, usually early in the morning when you get the minimum temperature before the sun rises. And it can be summarized in the following:
More than 20C: This is more like early autumn temperature, no problem here, if you run fast enough, the usual summer gear will suffice. This would be made up of running shorts, short sleeve coolmax shirt to wick sweat, long sleeved thin shirts will do as well to keep the chill off the arm. No cap or anything else is required.
Between 15-20C: Again, shorts will do, but now maybe a long sleeved shirt will be required. I started with a thicker synthetic long sleeved shirt, but it does feel quite warm after 30mins of warming up during the run. I think a thin shirt would do, but you just have to keep the activity high to keep warm.
Between 5-15C: Ok, this is a big temperature range. But I feel that in this range you will need at least long tights and a pair of long sleeved shirt. Towards the lower range, you might need a layer of baselayer below the long sleeved shirt as well. Ski shops sell those thin sweat wicking coolmax that will do quite fine. No cap seems necessary. There's no need to change your shoe as well, in this range I'm running with a standard pair of Asics Kayano with coolmax socks. At the lower temperature range, I would think that a wind blocking top will be required just to keep the wind from reaching your base layer. So... 2 layers for the top, and 1 layer for the bottom. What's recommended are windblocking (Gore Windstopper, etc) tops and long tights.
Down to freezing: Windblocking material seems to be a must for the top. I wear a pair of Asics World Performance 5000 top and bottom tights for this temperature. Both top and bottom has this layer of fleece (like Roubaix Pro material, etc) to trap a layer of air. At this temperature any wind will put the chill into you, so windstoppers are essential. Nothing special with the shoe, I wear normal summer shoes but just have to keep on moving. At this temperature, the wind will bite into your head as well, so beanies are essential to cover the ears. No need a balaclava... What pedestrians are afraid of is to see a person running towards them in tights and balaclava.