I have had several conversations about running in the winter in recent months. While I am far from an expert on the topic, I decided it would be kind of cool to share a few things that might help others in their winter runs.
As some of my friends know, I lived in Bozeman, Montana for nine years, and Anchorage, Alaska for two years. Also, I lived in Flagstaff, Arizona for two years (While talking about Arizona and snow in the same sentence might appear to be oxymoronic, my home in Flagstaff sat at almost 8,000'. I experienced, by far, more cold and snowfall here than any other year I lived in Montana or Alaska!). During those 13 winters, I ran regardless of snow or temperature, learning a lot in the process.
In my opinion, the key to winter running is layering. You then simply add or subtract as the climate so dictates. As for what I wear, I'll start from the top of my body and work my way down.
Head: I wear a synthetic wicking biker's skull cap (Pearl Izumi) anywhere from about 10 to 40 degrees. If it gets much colder than 10 degrees, then I switch to a SmartWool cap. It would have to drop well below zero before I would consider putting on a face mask.
Some people have trouble breathing in cold air while running and even develop coughs as a result. That was never a problem for me so I don't have much to suggest. I fooled around with a heat exchanger face mask when I was on a climb of Denali. Within a few miles, the condensation from my breathing froze up on the mask; I cached it right away and never used it again.
Top: If it's 25 to 40 degrees, say, then I wear a black Patagonia lightweight long sleeve top made out of Capilene. On top of this, I wear a black short sleeve top made out of Capilene. Very good material, easy to clean, and does a great job of wicking. If you are the type that gets cold easily, then you could consider using increasingly popular merino wool base layers. Capilene is wonderful stuff but does suffer from what I call "flashover". In other words, it does such a good job wicking sweat that if you stop, the sweat condenses on the outside of the material as hoar frost. You then get chilled. This isn't a problem for me because I'm never just sitting around on my runs. As far as its positives are concerned, merino wool, in my opinion, doesn't suffer from this as much, keeps you a bit warmer, and provides warmth even when wet. One popular brand among my outdoor/mountaineer buddies in Alaska and Montana is Ibex, but I'm sure SmartWool and Patagonia are good too.
Finally, on top of the two Capilene layers, I wear a Patagonia Nine Trails shell jacket. If it gets below 25, then I switch out the Nine Trails jacket with a nordic ski jacket I have from REI. The jacket is lightweight, and form fitting. The material is built up in the front to block the wind but of a substantially lighter weave in the back and top to allow for venting (this is the same idea as some biker's jackets I've seen). If it gets much colder than 10, then I add another layer of expedition weight Capilene on top of the two base layers.
Bottom: I wear Under Armour shorts all the way down to 25 (by the way, these aren't the shorts I use when racing). At 25 or below, I wear some Under Armour tights and put the shorts on top. For what it's worth, I use Capilene underwear too. If you wear cotton underwear, which absorbs sweat, then you are completely defeating the purpose of layering and wicking. If it got below 10, say, then I wear runner's underwear for men and I add a pair of Cloudveil Symmetry pants. Wonderful pants! This year I tried experimenting with CW-X PerformX Tights when it got below 10. On me, they run quite snug and tight; I have not made up my mind if I like them yet.
Hands: I use lightweight merino wool gloves from SmartWool from 25 to 40. Below this, I switch to an ice climbing glove from Cloudveil. Much below 10, and I wear the lightweight merino wool gloves inside a polarfleece mitten; you can add handwarmers if it is a long run.
Feet: This is a slamdunk. I like SmartWool merino wool crew socks. I wear these from 40 down to 10. If it gets much colder than 10, then I switch to a heavier grade merino wool hiking sock, also from SmartWool. Some people also like to wear gaiters for extra protection; I do not.
As for shoes, if the rail-trail or roads are relatively bare and dry, then I wear my usual running shoes (Brooks Launches these days). However, if there is more than 2-to-3" of snow on the rail-trail or roads, say, then I wear my trail running shoes (I recently upgraded to the new Brooks Cascadia 6's).
Finally, if the rail-trail or roads are icy, then I wear "cleats". Over the years, I have gone back and forth about cleats. Yaktrax never worked for me -- they either came off or I destroyed them. In Alaska, I switched over to something akin to Get-A-Grip's and those did seem to work. However, I had to replace the carbide spikes regularly. STABILicer SPORT's are nice but they are heavy and will pinch your toes together. Flagstaff was big-time Kahtoola country. While I have no experience with their MICROspikes, I heard some praise. My friend, wonderful ultrarunner Gancho Slavov, uses homemade spikes, or Screw Shoes, with satisfaction. This might be an inexpensive, good option although it is a pain in the ass to do this if you don't have a power drill. Finally, my friend WVU cross country runner Maria Dalzot showed me what might be the best option of all if you are a serious runner and have the money. They are called Ice Bugs and are essentially a running shoe with the cleats built into the outsole. This is what I'll try next winter.
You need to be careful doing a lot of running with cleats because it changes your stride and gait over the course of time. I tore a hip flexor by running all the time in cleats up in Anchorage a few years ago and it sidelined me for a couple months. This just before a Ranier climb :-(
Winter running certainly isn't for everybody. However, it never hurts to maintain a base heading into next running season. If anyone else has some ideas, then by all means chime in here! I've always enjoyed the silent solitude of a winter run and much prefer it to treadmill work in a gym. Try it; you just might like it! I have some great memories of running along the Coastal Trail up in Anchorage and looking up to see the shimmering Northern Lights, or rounding a bend in the trail to see a moose walking towards me. Those are memories I wouldn't trade for anything.