Below 5 is getting down there a bit, IMO. If you lived to ask about it (and know where your testicles are), you can probably handle it. I ran today in Lawrence at 10 degrees, and it felt pretty good, but there was barely any wind and I wore gloves, ear protection, nylon sweat pants and an old school gray cotton hoodie. I wouldn’t wear anything but running shoes though no matter how thin they are. Look for a treadmill on craigslist. There will be a bunch for sale really cheap in about a month!