Cold weather does not just occur in winter. It can also occur in early spring and late autumn. Mountain weather is inherently mercurial. Temperature drops about 2 ½ degrees Fahrenheit for every 1,000 feet of elevation gained. Wind velocity can vary by tens of knots due to the channeling effect of terrain. A rain storm can come out of nowhere. A balmy day can change into a hypothermic challenge in a matter of minutes.

The only reliable way of keeping warm in bitter cold weather is body heat. To generate body heat, you have to keep moving. If you are not in adequate physical condition to keep moving you should not be hiking in cold weather. It may not be safe to stop and rest. A fair number of people die from exposure every year due to exhaustion and the resultant hypothermia. Cold weather hiking is not for neophytes.

Cold weather hiking apparel consists of layers of lightweight clothing. The outer layers are removed in sequence for uphill exertions when heat is generated. They are stored in the backpack. This allows the heat to dissipate and reduces moisture accumulation. The layers are reapplied as needed to stay warm when stopping to rest or when the trail levels. When you stop, it is necessary to prevent the loss of heat. Most hiking clothing comes with Velcro straps to seal the extremities, including the neck.

A change of clothes for the end of the hike is considered by some to be a mandatory provision in the winter. When you finish the hike you stop generating heat. The dampness of your undergarments and socks persists, however, and, unless you stay in a warm car, you will get a chill. You will never really get warm again until you take a hot shower or bath. But dry clothes help.

Long Underwear (long sleeved shirt and pants) is essential for cold weather hiking. A synthetic fabric such as polypropylene wicks the moisture away from your skin very effectively. Silk long underwear is an alternative but it is not as good at removing moisture, though it dries faster. Synthetic long underwear come in three grades; light, medium and expedition. Expedition is the best choice to make sure you stay warm. The cotton long johns used by farmers and hunters do not work for hikers. When they get moist from the sweat generated by climbing, they do not dry. When you stop to rest you get cold and stay cold. It is not practical to change your underwear on a bitter cold day. When it is extremely cold (below 0 degrees F), a combination of silk long johns and polypropylene long johns (two layers) work every well. The silk is like a second skin and wicks the moisture to the polypropylene and you stay dry and warm.

Hiking Pants and Shirts made from wool work very well in cold weather. Wool is an excellent insulator and dries rapidly. It is the material of choice in Scotland where wet weather is endemic (and sheep are profligate). Some hikers prefer synthetic tight pants for winter hiking. Though sufficient, they are not necessary for heat retention. A wool shirt over a polypropylene or silk undershirt is an efficient system for wicking away moisture and dissipating it. The same applies to the pants, though wool pants are harder to find.

A Jacket is the top layer for the upper body. Synthetic insulating fabric jackets that extend to just below the waist work well. They allow heat to escape to reduce the effects of moisture on body temperature. Some new jacket materials have a wind resistant layer in addition to the insulating layer. These also work quite well. Wool jackets are too heavy and bulky to be stored in the backpack when not in use.

Wind Clothing consisting of a lightweight jacket and pants are necessary when wind chill becomes a factor. Even if you are wearing a wind resistant insulating jacket, a separate wind jacket is advisable. If a jacket without a wind resistant layer is used, a separate wind jacket is a necessity. Jackets with just the insulating layer are transparent to the wind. Wind jackets and wind pants should be about one size too large to fit over the underlying layers.

A Stocking Cap is the most efficient method of temperature control for mountain hiking. A substantial amount of generated body heat is dissipated from the head. The cap can readily be removed during strenuous uphill climbing to reduce sweating. It is the first thing you put back on when you stop to rest. A snug wool cap that covers the ears is best.

A Headband is a good addition to a well stocked pack. It is useful to keep the ears covered when it is cold and windy and you are climbing uphill. If you only have a stocking cap, you find that when you take off the cap to reduce sweating, your ears freeze. The headband allows for the heat to be dissipated from your head and keeps your ears warm.

A Neck Gaiter is a sleeve that fits over your head and covers the neck area like a scarf; however, it is better than a scarf since it has no loose ends and is snug. It can also be pulled up to cover the chin and the mouth when it is windy. A face mask can be added for full protection, but I personally find them very confining and prefer the combination of garments that afford adequate insulation.

Gloves are essential, as it is not practical to keep your hands in your pockets and negotiate uneven terrain. The arms are needed for balance and to break a fall if you stumble. Keeping your hands warm is the most challenging aspect of cold weather hiking, as they are isolated from the body and remain relatively static when hiking, unlike the feet. Mittens afford the best cold weather protection, but you can’t use your fingers should the need arise. The result is that the mittens must be removed frequently at the expense of keeping the hands warm. The best combination that I have found is synthetic running gloves that fit fairly snugly with loose mittens made from wool or wool-blend materials. For more extreme conditions, synthetic windproof mittens that go over the thinner fingered gloves have never failed to keep my hands warm. As with other clothing, layers are removed as conditions warrant.

Winter Footwear - Boots that are made with rubber lowers and leather uppers (a winterized version of the Maine hiking boot of LL Bean fame) are very good for hiking through snow, particularly when it is wet and slushy. Some leather boots are more waterproof than others and some claim to keep your feet dry. However, I know of no leather boot that will keep your feet dry for a full day of hiking along slushy trails.

Gaiters - If the snow is greater than about 8 inches, every step will result in snow over the boot top. Since this area is normally quite warm from the heat generated inside the boot, the snow melts and the result is wet feet. Gaiters (zip up leggings) cover the boot top area to prevent this problem. The type that go up to about the knee and are synthetic are best. Make sure you get a pair that are fairly easy to get on, as they can be cumbersome.

Socks - A good combination is a synthetic sock liner with a wool sock. As is the case with the clothing, the sock liner wicks away the moisture to the wool, which absorbs quite a lot before it gets saturated. Synthetic hiking socks work as well as if not better than wool socks. A spare set of liners and socks should always be carried, as you never know when your feet will get wet. This is especially true in cold weather, when wet feet can lead to frozen feet.

Ice Cleats - Ice cleats come in various shapes and sizes, but in essence they are studded sandals that strap onto boots for traversing ice. Ice is endemic to trails as the sun melts snow from upper elevations during the day which flows to lower elevations in perpetual shadow to freeze at night. When a trail is icy, as it often is, it is nearly impossible to negotiate on two feet. Sometimes even four won't work. It is generally a good idea to have a set just in case.

One last note. Cold weather implies winter, which in turn means shorter days and longer nights. The sun sets very early in December and it can get surprisingly dark in some mountain valleys as early as 4 PM. A good flashlight is absolutely essential in the winter. Even though this is part of the standard equipment for any time of the year, it is worth carrying spare batteries and making sure your flashlight is in good working order when Daylight Savings Time "falls back" at the end of October. It is generally a good practice to do a total pack inventory at this time of the year anyway. You never know what you are going to find at the bottom of your pack after a summer of hiking.