There are a lot of factors when trying to decide on what to wear- temperature at the start and finish of your run, precipitation, and wind. What you wear on one 10C run one day might differ from the next depending on if it's windy out, sun is shining, or the possibility of rain.
Note all the clothes I wear are made of technical fabrics that wick sweat away from your body. No cotton here! While it may look like it, this post was not sponsored by Lululemon! I just really like their clothes! I wish I was sponsored to write about them because I certainly have enough of their stuff!
~ Tank top, running skirt or shorts, headband
~ Tank top or t-shirt, running skirt or shorts and headband
~ Tank top, capris and headband
~ T-Shirt/tank top and capris and headband
~ Thin long sleeve shirt (OR T-shirt if sunny, no wind), capris, running vest (if windy) and headband
~ Thin long sleeve shirt, jacket (mine is thicker), long tights, warm headband and gloves (the last two are just to start- I normally take them off once I've warmed up)
~ Tank top, thicker long sleeve shirt, long tights, warm headband and gloves
~ Thick long sleeve shirt, tank top, jacket, long tights, neck buff, warm headband, gloves
~ 2 long sleeve shirts, jacket, warm long tights, hat, neck buff, warm gloves, warm socks
~ Short sleeve shirt, 2 long sleeve shirts, jacket, base layer pants, warmest tights, hat, neck buff, warm gloves with hand warmers, and wool socks
~ Tank top and running skirt since I'll likely be running indoors on the treadmill!
Hope that helps solve some of the mystery of what to wear when running.
Another rule of thumb that I use is if you are a bit chilly when you first go outside then you are dressed right since you will heat up soon after you start running. If you aren't cold when you first head out then you are going to overheat.
The key is to find out what works for you. Some people are comfortable wearing shorts when it's 5C, I am not! I greatly dislike wearing extra clothes around my waist since I already wear a water belt on my runs so I really try to avoid overdressing, even if that means being a tad chilly at the start.
Regardless of what you decide to wear on each run, it's also important to have dry clothes to change into after your run. Nothing worse than going for breakfast or even driving home in sweaty, cold clothes, especially when it's super cold outside!
If you have any questions, let me know!