These are the bottoms I run in:
https://www.columbia.com/men-baselayer-bottoms/
These are the tops I run in:
https://www.columbia.com/mens-heavy...ayer&dwvar_1638531_variationColor=054#start=0
For the most part these do the trick. They aren't perfect, but I've run in as low as -30F for over an hour and been fine. I mean, it's cold, but for me it's always been run outside or not at all.
For me it's:
50 and above - shorts and singlet
40 to 50 - shorts, singlet, and light gloves
30 to 40 - shorts, light long sleeve (like runDisney shirt), light gloves, and hat
20 to 30 - light thermal columbia pants, light thermal columbia long sleeve, medium gloves, and hat
10 to 20 - medium thermal columbia pants, medium thermal columbia long sleeve, heavy gloves, and hat (and jacket if easy day)
0 to 10 - heavy thermal columbia pants, heavy thermal columbia long sleeve, heavy gloves, balaclava, and jacket
-10 to 0 - heavy thermal columbia pants, second pair of pants, heavy thermal columbia long sleeve, heavy gloves, balaclava, and jacket
-10 and below - heavy thermal columbia pants, second pair of pants, heavy thermal columbia long sleeve, heavy gloves, balaclava, hand warmers, sunglasses, and jacket
When it comes to heat acclimatization time, I just shift downwards by 10-20 degrees or so. Therefore, if it is 20F in reality, I might treat it like it is 0F instead. The timing of this fits nicely into the normal taper pattern so it doesn't take much away from the training itself. Just be mindful to not linger outside much after the run and even consider cutting any cool down off. Because you'll be sweating up a storm, and putting yourself at a risk for hypothermia.