It rarely rains in the Nepal Himalaya in January, so the skies will be crisp and clear, and the mountain views at their best. However, it can snow at high altitude at any time. The higher in altitude you climb, the colder the temperatures will become. Average January temperatures in Namche Bazaar (11,290 feet) are between 18 and 43°F (-8 to 6°C). Although Namche is quite high, it's not as high as points further along the trail, which will be colder.
Crowds & Costs
Because winter is the low season, you will have no trouble getting a bed at teahouses along the Everest Base Camp trail or in the wider Everest region. However, some teahouses—especially at higher elevations—may be closed, as many of the local inhabitants head to Kathmandu for the winter. This is one reason (of many!) why trekking with a guide is a good idea—they know which places at which settlements remain open during the off-season.
While the costs of accommodation, food, and transport are unlikely to be much different in January than the rest of the year, the fact that there will be fewer travelers on the trail means you may be able to get better value for money. For example, flights to Lukla as well as the best teahouses fill up fast in peak season, meaning that if you don't book early, you might not get your first pick of flight times, or will have to settle for lower-quality accommodation (perhaps for the same price as somewhere nicer). In January, you're unlikely to have this problem.
The trails in the Everest region will be much less crowded in January than in the peak months of October or April, meaning you will have clear views almost to yourself. As EBC is Nepal's most popular and crowded trek, this has the potential to make a huge difference to your experience.
Some higher-elevation treks are not ideal in January. Aside from the cold temperatures, some will be impassable with snow. Treks that require crossing high passes (such as the Three Passes Trek) are not recommended in January, as they're likely to be snowbound. You should also expect to have to turn around at any point on any route if the weather turns bad and your guide thinks it's unsafe to continue.
However, trekking in January is no guarantee that this will be necessary. Sometimes snow cuts off routes much earlier or much later in the season, too. Treks that stay below 13,000 feet will be more comfortable, as well as safer, but even so, it's essential to check (or have your guide check) the weather conditions as you progress along the trek.
Unless you're a very experienced trekker and know you'll be comfortable with the colder temperatures at high altitude, you might prefer to take a shorter trek in the Everest region that doesn't go all the way to Everest Base Camp. By trekking to and basing yourself in Namche Bazaar, a two-day walk from Lukla, you can take a number of day hikes around the region. The views are likely to be spectacular at this time of year, and you're less likely to have altitude or temperature-related problems at Namche Bazaar.
Alternatively, you could take the 'Pioneers' Route' from Jiri to Lukla, so named because it was the trekking trail that early Western mountaineers took to access the Everest region before the airport was built at Lukla. Jiri is a day's drive from Kathmandu. Similarly, fly from Kathmandu to Phaplu and trek through the Solukhumbu region from there. Few trekkers these days take this trail through the Solukhumbu, and those that do find an interesting culture that contrasts quite markedly with the Sherpa culture of higher altitudes. These treks take 4-7 days, depending on which route you take. From Lukla, you could continue to Namche Bazaar and base yourself there for some day hikes, as mentioned above.
January is also an ideal time to consider splurging on a luxury tour. Travelers with a bit more money to spend will enjoy staying in some of the Everest region's finest lodges (such as Yeti Mountain Homes and Everest Summit Lodges). While this kind of trip is special at any time of year, it's even more so in winter, when you can retreat from the cold to a comfortable, cozy hotel that rivals boutique accommodation in the cities.
What to Bring
It's important to be well prepared for the cold in January, not just for your comfort but also for your safety. Although many teahouses will provide blankets, these won't necessarily be adequate for winter conditions. A sleeping bag made to keep you warm in -30°C conditions is ideal. While the sun will warm things up in the day, at the higher altitudes you will still need to trek in warm clothes, so bring a warm down jacket (down is ideal because it's light, so if you need to take it off and carry it in your bag during the day, you won't be weighed down by something bulky). Warm clothes for the evenings and nights are also essential, as well as good woolen hats, gloves, socks, and scarves.
Almost all winter equipment can be bought or rented at trekking shops in Kathmandu in case you don't have your own winter trekking gear and don't need it at home.
Getting There & Away
The quickest way of getting to the Everest region is to fly from Kathmandu to Lukla. While rain is less likely to cause delays and cancellations in January than in some other months, Kathmandu does experience fog in the winter. This has the potential to disrupt flights to or from Lukla, even if the conditions in the mountains are good.
Events in January
A trek in the Everest region could be the most memorable New Year's Eve you ever spend! To experience the nightlife and local bars in the mountains, aim to be in Namche Bazaar on December 31 to enjoy the festivities. Just remember that the effects of alcohol tend to hit harder and more quickly at altitude.
Traditional Nepali festivals (both Hindu and Buddhist) usually follow a lunar calendar (this means that a festival that falls in January one year may fall in December or February the next). A festival that is often, but not always, held in January is Lhosar. This Buddhist festival is held on the first day of the new year for Nepali ethnic groups that trace their history to Tibet, especially the Gurung, Tamang, and Sherpa people. As most people who live in the Everest area are Sherpas, if you happen to be traveling here during Lhosar, you may experience some festivities.